ACARE&REPAIRGUIDEFOR:LAWNMOWERS,SNOWBLOWERS&SMALLGAS-POWEREDIMPLEMENTS

EditedbyPeterHunn

ContentsIntroduction

THINGSTHATMAKEASMALLENGINERUN

•DefiningtheSmallEngine

•FiveBasicSmall-EngineSystems

•TheCompressionSystem

•The4-StrokeCycle

•OverheadValves(OHV):TheNewStandard

•FuelSystem

•IntotheCarburetor

•IgnitionSystem

•Lubrication&CoolingSystem

•BrakingSystem

•ElectricalSystem

•ToolstoKeepYourSmallEngineHappy

•SafeSmall-EngineServicing

MOTORMEDICALSCHOOL101

•LearningHowtoDiagnoseaMotor’sSymptoms

EASYBUTIMPORTANTMAINTENANCE

•End-of-SeasonMaintenance

•Checking&ChangingOilona4-Stroke

•ServicingSparkPlugs

•ServicingAirCleaners

•MoreSmartMaintenance

BASICENGINEREPAIRS

•BasicRepairs

•RemovingDebris

•ServicingtheFuelTank

•ServicingtheFuelFilter

•ServicingtheFuelPump

•ServicingtheCarburetor

•AdjustingtheGovernor

•ReplacingtheRewind

•Inspecting&ChangingtheMuffler

ADVANCEDREPAIRS

•OverhaulingCarburetors

•InspectingtheFlywheel&Key

•ReplacingtheIgnition

•TestingtheElectricalSystem

•RemovingCarbonDeposits

•ServicingtheValves

•ServicingtheBrake

2-STROKEPOWEREQUIPMENT

Index

Introduction

Unlessyou’reamongthesmallbutenthusiasticgroupof“motorheads”whocollect,troubleshoot,andrestorevintagelawnmowers,chainsaws,garden

tractors,snowblowers,oroldoutboardmotorsasahobby,youprobablyopenedthisbookbecausesomesmallengineinyourlifejustisn’trunningright.Maybeit’shardtostartorsometimesdoesn’tstartatall.Perhapsyoursmallengineruns,butsoundsstrange;likeit’sgotrealproblemssomewheredeepdowninside.

Quitepossiblyyou’rewishingyouhadthemechanicalequivalentofa“greenthumb”soyoucouldsavemoneyonsmall-enginerepairs.Withmostpowerequipmentshopscharginghourlyrepairratescomparabletothoseofaluxurycardealership’sservicedepartment,itisnowonderwhymanyfolkswhodon’tconsiderthemselvesparticularlyhandygetsodarnfrustratedbytheirpersnicketyweed-whackerormessed-upmowerthattheyfeelthere’snoalternativebuttobuyanewone.Withallduerespecttothosewholackconfidenceintheirabilitytokeeptheirlittlemotorspurringproudlyseasonafterseason,SmallEngines&OutdoorPowerEquipmentiswrittentoprovethemwrong.

NOTICETOREADERS

Forsafety,usecaution,care,andgoodjudgmentwhenfollowingtheproceduresdescribedinthisbook.Thepublishercannotassumeresponsibilityforanydamagetopropertyorinjurytopersonsasaresultofmisuseoftheinformationprovided.

Thetechniquesshowninthisbookaregeneraltechniquesforvariousapplications.Insomeinstances,additionaltechniquesnotshowninthisbookmayberequired.Alwaysfollowmanufacturers’instructionsincludedwithproducts,sincedeviatingfromthedirectionsmayvoidwarranties.Theprojectsinthisbookvarywidelyastoskilllevelsrequired:somemaynotbeappropriateforalldo-it-yourselfers,andsomemayrequireprofessionalhelp.

ORGANIZATIONOFTHEBOOK

Thisbookwalksyouthroughlotsof“realworld”mechanicalcuresandproblemprevention,basedonthemostwidelyusedsmall-enginedesigns.Youcanfindthestep-by-stepdirectionsforyourspecificmaintenanceorfix-upprojectintheTableofContents(page3)orbydelvingrightintooneofthesectionslistedbelow.Eachofferssafetytips,keytoefficientdiagnosis,andproficient

“wrenching.”

•“ThingsThatMakeASmallEngineRun”(pages6to33)identifiespartsofthesmallengineandoutlineshowtheyarearrangedintosystems:Theyarethecompressionsystem,fuelsystem,ignitionsystem,lubricationandcoolingsystem,brakingsystem,andtheelectricalsystem.Thischapteralsoidentifiesgoodtoolstohaveonhandforrepairwork,aswellassomepointersonsafesmall-engineservicing.

•“MotorMedicalSchool101”(focusesontroubleshootingthatpooroldmotor’sfunnynoises…ormaybegettingittosaysomethingnicetoyouagain(pages34to41).

•“EasyButImportantMaintenance”(pages42to65)offersaconvenientscheduleandchecklistforinspectingandchangingtheoil,sparkplugs,andfilters.

•“DoctoringTheAilingEngine”“BasicEngineRepairs”(pages66to95)and“AdvancedRepairs”(pages96to137),guideyouthroughbeingabletoandrepairofthemostcommonproblems.Alsocoveredareenginemaladies,thatsomemightconsidertobeabitmorechallenging.

•“2-StrokePowerEquipment”(pages138to143)introducesyoutothebasicsof2-strokeengineoperationandthenguidesyouthroughbasicmaintenanceandrepaircommontooutdoorpowerequipmentimplementssuchaschainsaws,stringtrimmers,snowblowers,andgasblowers.

ThingsThatMakeaSmallEngineRun

DefiningtheSmallEngine

Thebiggestdifferencebetweensmallgasolineenginesandothertypesoffuel-burningmotorsistheirsmallcapacityandsimplicityofdesign.Smallenginesgeneratemodestamountsofpower—generally2to25horsepower—comparedtoatypicalfamilycarboasting150ormorehorses.Andasmallengine’scompactsizealsomakesiteasiertomaintainandrepair.

Atypical4-stroke,overheadvalvegasengine.At6.5horsepoweritisofaveragepowerforalawnmower.

Becausesmallenginesaredesignedforrelativelysimpletaskslikecuttinggrassandblowingsnow,theirconstructionisuncomplicatedcomparedtootherengines.Unlikecarsandothervehiclesthatfrequentlyaccelerate,slowdown,oridleforlongperiods,smallenginesareusuallyrunatconstantspeedorchangespeedslightlywhenencounteringmodestchangesinthe“load,”suchaswhenalawnmowerhitsapatchofthickgrass,orwhenasnowblowertriestodigestapileofpackedsnowrecentlyshoveledofftheroofandintothedriveway.

Also,unlikecarengines,smallenginesdon’thavetobewedgedbetweenaradiatorandfirewallinanautomotivechassisorgetlinkedtocountlesscomputersandotherelectricaldevices.Thismakessmallenginepartseasiertoinstall,adjustandremove.Inmanycases,youcanreacheventhemosthiddensmallenginepartswithjustafewturnsofawrench.

ESSENTIALSOFTHE4-STROKEENGINE

Exceptformostchainsaws,stringtrimmers,leafblowers,andlight-dutysnowblowersthatuse2-stroke(alsoknownas2-cycle)engines(see2-StrokePowerEquipmentonpage138),themajorityofsmallpowerplantsareofthe4-stroke(or4-cycle)variety.Thesediminutive4-strokesfollowthesameessentialoperatingprinciplesasautomotiveengines.Touseabakerymetaphor,thelittlemillsonlawnmowerswouldbeconsideredcupcakescomparedtothefar-larger,multitieredconfectioncreatedforafancyweddingreception.Nomattertheintendedapplication,however,here,initssimplestform,ishowa4-strokeengineworks:

Whenyoupulltherope,knownasarewindcord,oruseyourelectricstarter,preciseamountsoffuelandfilteredairmixtogetherinthecarburetor.Themixturerushesintotheenginetobecompressed,ignited,andburnedinacontrolledprocessknownasinternalcombustion.Thisproduceshotgases.Asthesegasesexpand,theypushasmooth,well-lubricatedcylindricalcomponent,knownasthepiston.Thepiston,inturn,drivesthecrankshaft,thearmthatspinsabladeorperformsotherwork.Movingvalvesona4-strokeengine(andstationaryportsinthecylinderwallona2-strokemotor)letairandfuelintothecombustionchamberabovethepistonandallowspentgasestoexitthroughthemuffler.Pullingvigorouslyonthatcordorturningthestarterkeygetsthisprocessmoving.Whenitworkscorrectly,itcoaxesthefuel-airatomization,fuel-aircompression,ignition/spark,andexhaustofburnedgasestoworkonitsown.Itisdesignedtobecomeself-sustainingfromthetimetheenginestartsuntilthemomentitstops.Timedelectricalsurgescausethesparkplugtofirerepeatedlyinsidethecombustionchamber,ignitingeachfreshsupplyofairandfuelandproducinggasesthatcontinuallydrivethepistonandcrankshaft.Allthewhile,oilfromthecrankcaseandaircirculatetokeepenginetemperatureswithinanacceptablerange,andagovernormonitorschangesintheworkloadandadjustsenginespeedaccordingly.There’salotbeingaskedofasmallenginewhenthestarterissuddenlyengaged.That’swhyanenginemightsoundlikeit’stakingasecondortwotofullycometolife,thewaysomebodymightwhenrousedoutofawarm,comfortablebedwhentheclockradioalarmfiresuponawinter’s

morning.Two-cycleenginescompletethis“wake-up”routineintwopiston“strokes”(oneup,onedown,orone360-degreerotationofthecrankshaft).Fora4-cycleengine,thewholeprocessinvolvesfourmotionsofpistontravel(twoupstrokesandtwodownstrokes,ortwofullcrankshaftrotations.

Fivebasicsmall-enginesystemsTherearefivesystemsatworkineverysmallengine:fuelsupply,compression,ignition,lubricationandcooling,andgovernor(speedcontrol).Eachofthesesystemsisexplainedindepthinthefollowingpages.

Twoothercommonsystems—startersystems,whichrequireabattery,startermotor,andelectricalrechargingsystem,andbrakesystems,whichstoptheengineifyouletgoofthecontrols—arealsodiscussedindetail.Inshort,thesefivesystemsgeneratethepowertospinablade,turnawheel,orperformotherwork,whilethetwoothers—startersandbrakingsystems—increasesafetyandconvenience.Thefollowingpageswillfamiliarizeyouwiththemajorpartsinthesesystemsandtheessentialsofhowtheywork.

PartsoftheFuelSystem

PartsoftheCompressionSystem

PartsoftheIgnitionSystem

PartsoftheLubricationSystem

PartsoftheCoolingSystem

ENGINECOMPONENTSANDTHEIRFUNCTION

Here’showthecomponentsinyourengineinteracttostartandmaintainthecombustionprocess:

TYPICALSMALLENGINESFORCONSUMERPOWEREQUIPMENT

7HPHorizontalShaftSingleCylinderUses:Smalloutdoorpowerequipment(edgers,pressurewashers,shredders,tillers,etc.)

26HPVerticalShaftV-TwinUses:Lawntractors

TheCompressionSystemTheinventorsofthefirstinternalcombustionenginesdiscoveredthatfuelburnsmoreefficientlyifcompressedinasealedchamberbeforeburningit.Compressionoftheair-fuelmixtureinthesmall4-strokeenginebeginsastheintakevalvecloses(orasthepistoncoversthecylinderportsona2-strokemill).Thetrappedvaporsarepushedtowardthecylinderheadbythepistonandcompressedintoaspaceaboutone-sixththeiroriginalvolume.Theexactamountofcompressionisanindicatorofanengine’sefficiency.That’swhyatightlysealedcombustionchamberissoimportantforgoodengineperformance.

VALVESONA4-STROKEENGINE

Valveslocatedinthecombustionchamberletfuelvaporsandairenterthecylinderandletexhaustgasesexitatpreciselytimedintervals.Atypical4-strokesmallenginecontainsoneintakevalveandoneexhaustvalvepercylinder,andmostsmall4-strokeengineshaveonecylinderanduseanL-head(orflathead)design,wherethevalvesareinstalledinavalvechambernexttothepiston.Overheadvalve(OHV)designsoffergreaterefficiency,however,andareincreasinglypopularwithconsumers.Inthisdesign,thevalvesarelocatedinthecylinderheaddirectlyinlinewiththepistonandaremovedbypivotingrockerarms.

PISTON

Thepistonridesthroughthecylinder,muchasaplungerridesthroughthechamberinahand-operatedairpump.Attheappropriatemoment,thecylinderissealedsothattheair-fuelmixtureiscompressedasthepistonmovestowardthecylinderhead.Whenthemixtureisignited,rapidlyexpandinggasesforcethepistonbackdownthroughthecylinder.While4-strokeenginestypicallyhaveflat-toppedpistons,2-strokeownersgettingintotheirengineswilldiscoverpistonswithanexhaustdeflectorcastintothepistoncrown.

RINGS

Thepistondiameterisnarrowenoughtopermitathinspacearounditforacoatingofoil.Flexiblepistonrings,installedingroovesinthepiston,workinconcertwiththeoiltocreateasealbetweenthepistonandthecylinderwall,thusensuringgoodcompression.Asthepistonispusheddownthroughthecylinder

byexpandinggases,aconnectingrodtransferstheforceofthosegasestotheflywheel.It’stheflywheel’smomentumthatperpetuatestheengine’s4-strokecycle.

COMPRESSIONPROBLEMS

Toolittleortoomuchcompressioncandamagepistons,rings,valves,valveguides,valveseats,andthecylinderwall.Lossofrecommendedcompression(measuredinpoundspersquareinch)canpreventanenginefromstartingatall.Ona4-stroke,ifanexhaustvalveleaks,exhaustcanbackupintothecylinder,causingprematurewear.Toomuchcompressioncancausetheair-fuelmixturetoburntoofast,causingknockingorpinging.Excesscompressioncanalsoleavecarbondepositsthatfurtheraggravateproblems.

PARTSOFTHECOMPRESSIONSYSTEM

The4-StrokeCycleInmostengines,includingtheoneyou’llfindonyourcar,andmostprobablyyourlawnmower,tractor,tiller,woodchipper,orotheroutdoorpowerequipment,combustionoccursina4-strokecycle.The4-strokecycleinvolvesfourdistinctpistonstrokes(intake,compression,power,andexhaust)thatoccurinsuccession.Foreachcompletecycle,therearetwocompleterotationsofthecrankshaft.

THEINTAKESTROKE

Duringtheintakestroke,amixtureofairandfuelisintroducedtothecombustionchamber.TheintakevalveisopenandthepistonmovesfromTopDeadCenter(TDC)toBottomDeadCenter(BDC).

Tounderstandwhathappensnext,thinkofthesuctionproducedlikeasyringedrawingliquid.Thishappensbecauseastheplungerinsideslidestowardthehandle,itcreatesalow-pressureareaatthetip.Apistonperformstheidenticaltask.AsthepistonmovestowardBDC,itcreatesalow-pressureareainthecylinderanddrawstheair-fuelmixturethroughtheintakevalve.Themixturecontinuestoflow,duetoinertia,asthepistonmovesbeyondBDC.OncethepistonmovesafewdegreesbeyondBDC,theintakevalvecloses,sealingtheair-fuelmixtureinsidethecylinder.

THECOMPRESSIONSTROKE

CompressionoccursasthepistontravelstowardTDC,squeezingtheair-fuelmixturetoasmallervolume.Theair-fuelmixtureiscompressedforamoreefficientburnandtoallowmoreenergytobereleasedfasterwhenthemixtureisignited.Thinkaboutthewarninglabelonpressurizedspraycans:Keepcontentsawayfromfire.Thisisnotonlybecausethecontentsareflammable,butbecausepressurizationmakesthempotentiallyexplosive.

Ifanenginehastoperformsomuchworkjusttobringtheair-fuelmixturetothepointofcombustion,wheredoesitfindtheabilitytoperformwork?Thisabilityderivesfromthefactthattheenergyrequiredforcompression—andstoredintheflywheel—isstillfarlessthantheforceproducedduringcombustion.Inatypicalsmallengine,compressionrequiresone-fourththeenergyproducedduringcombustion.Thesurplusdrivesthepowerstroke.

THEPOWERSTROKE

Theengine’sintakeandexhaustvalvesarenowclosed.Atapproximately20degreesbeforeTDC,thesparkpluginitiatescombustion,creatingaflamethatburnsthecompressedair-fuelmixture.Thehotgasesproducedbycombustionhavenowaytoescape,sotheypushthepistonawayfromthecylinderhead.Thatmotionistransferredthroughtheconnectingrodtoapplytorquetothecrankshaft.

THEEXHAUSTSTROKE

AsthepistonreachesBDCduringthepowerstroke,thepowerstrokeiscompleted.Theexhaustvalveopens,allowingthepistontoevacuateexhaustasitmoves,onceagain,towardTDC.Withthechamberclearedofexhaust,thepistonreachesTDC.Anentirecycleiscomplete.

1.IntakeStroke

2.CompressionStroke

3.PowerStroke

4.ExhaustStroke

OverheadValves(OHV):TheNewStandardLocatingthevalvesnexttothepistonisjustonewaytoconfigureanengine.Engineersfiguredoutlongagothattheycouldgainasignificantadvantageinmanyhigher-horsepowerenginesbyinstallingthevalvesinthecylinderheadsothattheyfacethepiston.Pivotingrockerarms—movedbypushrods—openthevalves.

Oneofthemainadvantagesofoverheadvalvedesignisamoresymmetricalcombustionchamber,resultinginamoreefficientburningoftheair-fuelmixture.Youmayseetheletters“OHV”imprintedontheshroudofyourenginetoindicatetheuseofoverheadvalves.

FuelSystemThemostcommonrepairsinvolvethefuelsystem,whichincludesthefueltank,fuelfilter,fuelline,fuelpump(onsomemodels),andcarburetor.

Youmayhaveheardpeoplejokinglycommentthatthefuelinthetankissolowtheengineisrunningonfumesor“vapors.”Technically,they’reright.Gasolinewon’tburninitsliquidstate;itmustbeconvertedtoavaporfirst.Thevaporsthatburninyoursmallengineareformedfromamixtureoffuel(typicallygasoline)andair.Andyouneedtherightamountoffuelandtherightamountofairtomaintainwhateverenginespeedyouselect.Thebestwaytounderstandthefuelsystemistobeginatthetank.

FROMTHEFUELTANKTOTHECARBURETOR

Locatethefueltankonyourengine.Ifyouhaveanolderengine,itstankisprobablymadeofsteeloraluminum(subjecttorustorcorrosion).Newertanksaremadeofplasticandarebuiltintothemoldedplasticshroudovertheengine.Now,lookforafuelline,ahoseconnectedtoonesideofthetank.Thefuellinecarriesthefueltothecarburetor,amixingchamberthatcontainsathrottleand(ifequipped)achoke,attachedtotheequipmentcontrols.

Onmostengines,theforceofgravitycarriesthefuelthroughthefuelline.However,ifthefueltankismountedlowontheengine,gravitymaynotdothetrick.Inthiscase,afuelpumpuseslowpressureinthecrankcasetopumpfuel.Thepumpislocatedbetweenthetankandthecarburetororinthecarburetoritself.Someengineseliminatetheneedforeitherafuellineorpumpbymountingthecarburetordirectlyonthefueltankandusingapick-uptubeinthetanktodrawfuel.

Locatingthefueltankisnotdifficultatall.Modernpushmowersusuallyhaveplastictanksthatarebuiltintotheshroud.Onsmallerhandheldpowerequipmentthefueltankisoftenopaqueplasticandmountedatthebottomofthetool.

IntotheCarburetorOnmostengines,fuelfromthefuellineentersthecarburetor’sfuelbowl,areservoirwhereafloat(similartothefloatballinatoilettank)regulatesthefuellevel.Fromthere,ameteringdevicecalledajetletsfuelintotheemulsiontubeinsidethepedestal,wherefuelandairfirstmix.(Oldermodelsincludeanadjustablejet;newermodelscontainafixedjet.)Fueltravelsthroughtheemulsiontubetothemainpassagewayinthecarburetor,calledthethroatorventuri,wherefurthermixingoccurs.Ifyourcarburetorisatank-mountedtype,fuelfromthetankmaybesupplieddirectlytotheemulsiontube,withouttheneedforafloat.

THEROLEOFTHETHROTTLE

Atoneendofthethroatisathrottleplate.Thethrottleplateisconnectedtoyourequipmentcontrollever(oftenreferredtoasthethrottle)andopensorclosestoincreaseordecreaseenginespeed.Asthethrottleplateopens,moreairisdrawnintothecarburetor.Airflow,inturn,determineshowmuchfuelisdeliveredforcombustion.Manycarburetorshaveanidlespeedscrewtostopthethrottlefromclosingtoofaratlowspeed,andanidlemixturescrew,whichincreasesordecreasesairandfuelflowtopreventastall.

USINGTHECHOKE

Athrottleworksfineinwarmweather.Butwhenit’scold,fluidsdon’tvaporizeaseasily.Theenginemayneedextrafueltostart.Thisistheroleofthechokeplateorprimer.Theycompensateforthecoldbyincreasingthefuel-to-airratio.Thechokeislocatedinthethroatbetweentheairfilterandthethrottleplate.Closingthechokereducesairflow.Lowpressurecreatedinsidetheenginekeepsthefuelflowing.Theuseofthechoke“enrichesthemixture.”It’snotaneffectivewaytorunanengineallthetime,butithelpsacoldenginestart.Oncetheenginereachesitsnormaloperatingtemperaturerange,youcanopenthechoketoletinmoreair,foracleaner,moreefficientburn.

Enginespeediscontrolledbythethrottle,agrippableleverthatopensandclosesthethrottleplate.

PARTSOFTHEFUELSYSTEM

UNDERSTANDINGCARBURETION

Inessence,acarburetorisapassagewaythatdrawsinairandfuelandsuppliesamixtureofthetwotothecylinder.It’sthenarrowingofthepassageway—calledthethroatorventuri—thatcausesthecarburetortodrawinthetwocomponentstheengineneedsforcombustion.Basicphysicstellsusthatairspeedwillincreaseatthenarrowpointandairpressurewilldrop.Sincefluidsflowtolow-pressureareas,fuelfromthebowlortankisdrawnintothethroat,mixingwithairtoformacombustiblevapor.

IgnitionSystemIgnitionsystempartsincludetheflywheel,ignitionarmature,magnets,sparkplug,andsparkpluglead.

Theignitionsystemplaysacentralroleinthestartingofyoursmallengine.Whetheryoustarttheenginewithatugontherewindropeortheturnofakeyonanelectricstartermotor,you’rerelyingontheignitionsystemtoproduceasparkinsidethecombustionchamber.

Theignitionsystemincludesmagnetsmountedinthesurfaceoftheflywheel,andanignitionarmaturemountedadjacenttotheflywheel,containingcopperwirewindings.Italsoincludesthesparkpluglead(attachedtothearmature)andthesparkplug.

Whenyoupullontherewindrope,youareturningtheflywheel,aheavymetalwheellocatedundertheblowerhousing.Witheachturn,themagnetsmountedinthesurfaceoftheflywheelpasstheignitionarmature,inducingelectricalflowthatproducesahigh-voltagesparkatthetipofthesparkplug.Theignitionsystemiscoordinatedwiththetimingofthepistonandthemotionofthevalvessothatthesparkwillignitetheair-fuelmixtureinthecombustionchamberjustasthepistonreachesthepointofmaximumcompressionineachenginecycle.

Oncetheengineisrunning,theflywheel’sinertiakeepsthecrankshaftspinninguntilthepiston’snextpowerstroke,whiletheflywheelmagnetsinducevoltageinthearmaturetokeepthesparkplugfiring.

SOLID-STATEIGNITIONSYSTEMS

Ittakes10,000to20,000voltsofcurrenttoproduceasparkatthetipofasparkplug.That’senoughtogiveapersonapowerfuljolt.Today’signitionsystemsaccomplishthisusingatinytransistorintheignitionarmature.Eachtimethemagnetsapproach,thetransistorestablishesanelectricalcircuit,alsocalled“closing”acircuit.The2to3ampsofcurrentproducedarethenconvertedtohigh-voltagecurrentthattravelsthroughthesparkplugleadtothesparkplug.

BREAKERPOINTIGNITIONSYSTEMS

Breakerpointsystemsarefoundonsmallenginesbuiltuntiltheearly1980s.Theyfunctionmuchlikesolid-stateignitions,butuseamechanicalswitch,insteadofatransistor,toclosetheelectricalcircuitrequiredtoproduceahigh-voltagesparkatthesparkplugtip.Apairofnickel-platedbreakerpointsremainapartformostofthe4-strokecycle(andhalfthattimeona2-strokeengine).Aflatspotmachinedintothecrankshaftcausesoneofthepointstopivottemporarily,closingthegapbetweenthetwoandclosingacircuit.

BUYINGSYSTEMPARTS

Ignitionsystemsaredesignedtooperateefficientlywithspecificallydesignedcomponentsandshouldnotbealtered.Whenyouneedtoreplaceparts,usetheoriginalmanufacturer’sreplacementpartsorquality“generics”madewithyourparticularengine’sspecificationsinmind.

PartsoftheIgnitionSystem

Lubrication&CoolingSystemLubricationpartsofa4-strokemillincludethecrankcase,drainplug,oilfillcap,oildipperorslinger,andoildipstick.Aircoolingpartsincludethecylinderheadcoolingfinsandflywheelfins.

Exhaustgasesandradiantheatemittedfromenginecomponentscarryoffmuchoftheheatproducedbyasmallengine,butnotenoughtokeepanenginerunningreliably.Thelubricationandcoolingsystemisdesignedtohandlethattask.Asalubricant,oilnotonlycarriesawayheat,itreducesamajorsourceofheat—frictionbetweenenginecomponents.Airflowalsoservesasecondaryfunctiononsomeengines,triggeringtheairvaneinapneumaticgovernor.

REDUCINGFRICTIONWITHOIL

Viscosityisthemostimportantqualityofengineoil.Itisameasureofanoil’sabilitytoresistmotion.Thisqualityiscriticaltooil’sperformance,sincemovingpartsconstantlytrytopushoil,muchasaplowpushessnow.Oilmustresistthisforcesoitcanmaintainacontinuousfilmthatkeepsthepartsthemselvesfromtouching.

Whileviscosityallowsoiltoclingtosurfacesandresistthesnowploweffect,italsoreducestheabilitytoflowatlowtemperaturesorwithintightclearances.Amoreviscousoilalsotakeslongertoreachitsoptimaltemperature.Andwhileoilgradesaregenerallyacompromisethattriestoanticipatetypicaloperatingconditions,acommonrecommendationfor4-strokesmall-engineoilisSAE(SocietyofAutomotiveEngineers)30four-cycleoil.

Someoilsarealteredtomakethemlessviscousduringthewinter.Thesemulti-viscosityoilshaveratingssuchasSAE10W-30.The10Windicatesalowerwinterviscosity.Atnormaloperatingtemperatures,theoilactslikeSAE30oil.Two-strokeoilistypicallydividedintocategoriesforair-cooled2-cycleenginesorforwater-cooledmotorssuchasoutboards.Theformerrunshotterthanthelatter,butsyntheticoilsarearguablybestforboth.Nomattertheenginetype,alwaysfollowtherecommendationofyourengine’sowner’smanualwhenselectingtheproperoil.

Engineoilisformulateddifferentlyfordifferenttypesofoutdoorpowerequipment,butthisSAE30oilwillworkinall4-cycleengines,lawnmowersorotherwise.

USINGMULTI-VISCOSITYOIL

Multi-viscosityoil,suchasSAE10W-30,isdesignedtoworkwellincoldweather.It’snotthebestchoiceifyoutypicallyoperateyourequipmentatorabove40°F.Inwarmweather,multi-viscosityoilislikelytocauseprematurecarbonbuild-upandlossofenginepower.Two-strokeenginesrequireoilspecificallylabeledfor2-cycleengines.

GETTINGOILTOCIRCULATE

Most4-strokesmallenginesrelyonthesplashingmotionofadipperorslingerinthecrankcasetodistributeoil.Onahorizontalcrankshaftengine,adipperisattachedtotheconnectingrod.Itpicksupoilintheoilreservoirlocatedinthecrankcaseandspreadsitacrossbearingsurfacesasthepistontravelsthroughthecylinder.

Aslingerisusedonmanyverticalcrankshaftengines.Itconsistsofaspinninggearwithpaddlescastintotheplasticgearbody.Partoftheslingerissubmergedintheoil.Asthecrankshaftturns,theslingerdispersesoilthroughoutthecrankcase.

KEEPINGA4-STROKE’SOILCLEAN

Smallenginesdesignedfortractorsandotherheavy-dutyequipmentmayincludeanoilfilter.Thepleatedpaperinsideremovesdirt,metalparticlesandotherforeignmatterthataccumulatesintheoil.Ifthepaperbecomesclogged,oilisreroutedthroughaspring-loadedbypassvalvetoensurelubricationevenwhenoilisverydirty.Evenifyourenginehasanoilfilter,youneedtoinspecttheoileverytimetheengineisruntomakesuretheleveliscorrectandtheoilstillhasitscleanambercolor.

COOLINGWITHAIR

Anenginereliesonaircirculatingaroundenginepartstomaintainanacceptableenginetemperature.Finsontheoutsideofthecylinderblockandcylinderheadimprovetheengine’scoolingabilitythewaypipesdoonacarradiator—byincreasingthesurfaceareathatradiatesheatandisexposedtocoolair.Althoughairisnotthemostefficientwaytotransferheat,itisplentifulandusuallyoffersasubstantialcoolingeffect.

Adifferentsetoffins—theflywheelfins—arealsoanimportantcooling

feature;astheyspintheydistributeairtomanyengineparts.Theblowerhousingandairguidesrouteairtotheflywheelfins.Onsomemodels,arotatingscreenovertheflywheelpreventsgrassandotherdebrisfromcloggingtheflywheelfins.Thescreenblocksdebrisfromenteringorcutsitintosmaller,lessharmfulparticles.

ADDITIONALCOOLINGCOMPONENTS

Someenginesrequireadditionalaircoolingandcontainacoolingairplenum,aductthatprovidesaseparatemeansforoutsideairtoentertheengine.Somecontainanairdischargethatdirectshotairawayfromtheengine.

GOVERNORSYSTEM

Amechanicalgovernorincludesgears,agovernorcrank,governorsprings,flyweights,andlinkages.

Thegovernorsystemislikeacruisecontrolsystem.Itkeepstheenginerunningatthespeedyouselect,regardlessofchangesintheload.Youcanthinkoftheloadastheamountofworktheenginemustperform:foramower,theheightofthegrass;foratiller,thedepthofthetines;forachipper,thethicknessofthebranches.Withoutagovernor,youwouldneedtoadjustthethrottlemanuallyeachtimeyourlawnmowerranacrossadensepatchofgrass.Agovernordoesthejobforyoubydetectingchangesintheloadandadjustingthethrottletocompensate.

Thegovernorsystembehaveslikeanunendingtugofwarbetweenoneortwogovernorsprings,whichpullthethrottletowardtheopenposition,andaspinningcrankshaft,whichtriestoclosethethrottle.Whentheloadontheengineincreases—atypicalexampleiswhenyoumoveyourrunninglawnmowerfromthedrivewaytothegrass—crankshaftrevolutionsdrop.Butthegovernorspringisstilltugging,causingthethrottleplatetoopen.Inresponse,alargervolumeofair-fuelmixtureentersthecarburetor,increasingenginespeedtocompensatefortheincreasedload.Thecrankshaftspeedsup,andthetugofwarresumes,untilanewequilibriumisachieved.Witheachchangeinload,thetensionbetweenthegovernorspringandtheloadbringsaboutanewequilibrium,knownastheengine’sgovernedspeed.Neithersidewinsuntiltheengineisshutoff.Atthatpoint,withoutthecrankshaftspinning,thegovernorspringpullsthethrottletothewide-openposition.

Twotypesofgovernorarecommononsmallengines—mechanicalandpneumatic.

MechanicalgovernorAmechanicalgovernorusesgearsandflyweightsinsidethecrankcase

asaspeed-sensingdevicethatdetectschangesintheloadandadjuststhethrottleaccordingly.

Pneumaticgovernor

Apneumaticgovernorusesamovableairvane,madeofmetalorplastic,asaspeed-sensingdevicebyregisteringthechangeinairpressurearoundthespinningflywheel.

Mechanicalgovernor

BrakingSystemSmall-enginebrakingsystemsincludeabrakebandorpad,brakebracket,brakecover,brakespring,stopswitch,andstopswitchwire,alldesignedtostoptheenginequickly.

Intheolddays,youcouldleaveyourlawnmowerortractoridlingwhileyousteppedintothegarageforarake.Today’ssmallenginecontainsanautomaticshutoffsystemdesignedtoprotectyouandothersintheareabystoppingtheengineanytimeyouletgoofthecontrolsorclimboffoftheequipment.

Manysmallenginescontainabrakethatappliespressuretothesmoothsurfaceontheflywheel.Thebrake’ssurfaceareavariesinsize,dependingontheequipment.Somemodelsuseabrakepad.Othersuseabrakeband,appliedtoalargerareaontheflywheel’ssurface.Botharehighlyeffectivewhenproperlymaintained.

Mostenginescontainoneormorestopswitcheswiredbetweentheengine’signitionsystemandengineandequipmentcomponents.Youcantriggertheswitchbyreleasingthebrakebailorremovingthegrassdischargeunitonalawnmowerorbystandingupfromtheseatofalawntractor,triggeringaswitchundertheseat.

Theswitchcutspowertotheenginebygroundingoneofthecopperwindingsintheignitionarmature.Whenthebrakebailisreleased,awireattachedtothearmatureisgroundedagainstametalenginepart,stoppingtheengine.Iftheengineisequippedwithabrake,thebrakepadorbandsimultaneouslyappliespressuretotheflywheel.Whenproperlymaintained,thetwocomponentsofthebrakingsystemstoptheenginewithinthreeseconds.

ElectricalSystem

Asmall-engineelectricalsystemtypicallyconsistsofanalternator,rectifier,regulator,and12-voltbattery.Thealternatoritselfconsistsofanassemblyofoneormorecopperwindings—collectivelyknownasthestator—andasetofmagnets.Liketheignitionsystem,thealternatorcreatesamovingmagneticfieldtoinducecurrent.Moststatorsconsistofabandofnon-adjustablewindingsmountedundertheflywheelandasetofmagnetscementedtotheinsidesurfaceoftheflywheel.Onsomeengines,thestatorconsistsofanadjustablearmaturemountedoutsidetheflywheelthatreliesonthesamemagnetsastheignitionarmaturetochargethebattery.Theresultislongerperiodsoftimebetweensurgesofvoltageandcurrent.LimitedamountsofDCvoltageandcurrentareproduced,andacapacitorisusedtohandlefluctuationsinthevoltageoutput.

ALTERNATINGCURRENTVS.DIRECTCURRENT

Anelectricalsystemcanbesetuptoproduceeitheralternatingcurrent(AC)ordirectcurrent(DC).Ifyourequipmentrunslightsandnobatteryorotherelectricaldevices,thealternatoroperatesmuchlikethegeneratoronabicyclewheel,keepingthelightsrunningwithACaslongasthebikewheel(ortheenginecrankshaft)isspinning.Ifyourequipmentincludesabatteryandvariouselectricaldevices,arectifierisattachedtothealternatortoconvertACpowertoDCsoitcanbestoredinthebattery.DCpowercanrunlightsevenwhentheengineisoff,aswellasastartermotor,electriccuttingbladeclutch,winch,andotherdevices.SomeenginessupplyACforlightsandDCforotherdevices.

Enginesthatoperateathighspeedsalsorequirearegulatororacombinedregulator/rectifiertomaintainasteadyvoltageoutput.

ToolstoKeepYourSmallEngineHappyAcombinationofgeneralpurposeandspecialtytoolswillfillyourmechanic’stoolbox

Therighttoolsmakeyourmaintenanceandrepairprojectseasierandmoresuccessful.Havethesetoolsavailable:

Small-enginetools

(A)Valvespringcompressor(B)Sparktester(C)Sparkpluggauge(D)Tangbendingtool(E)Tachometer(F)Feelergauges

(G)Ratchettorquewrench(H)Starterclutchwrench(I)Oilevacuatorpump(J)Flywheelpuller(K)Flywheelstrapwrench(L)Multimeter

General-purposetools

(A)Socketset(B)Standardscrewdriver(C)Phillipsscrewdriver(D)Partscleaningbrush

(E)Powerdrill(F)Puttyknife(G)Shot-filledmallet(H)Centerpunch(I)Flatfile(J)Needlenosepliers(K)Adjustablepliers(L)Star-shapeddriverset(M)Standardpliers(N)Adjustablewrench(O)Wirecutters(P)Baster(Q)Fuellinecrimper(R)Combinationwrenches(S)Hexwrenchset(T)Lockingpliers

MORESPECIALTYTOOLS

It’swisetohavethecorrecttoolsforeachjob.And,this“rightstuff”willsaveyoutime,too.Usingothertoolsassubstitutescandamageyourengine,tryyourpatience,andmaycreateasafetyhazardthat’llhavesomeonesaying,“Itoldyouso!”Whenbuyingtools,choosethehighestqualityyoucanafford.Shoparound—fromgaragesaleshostedbynewlyretiredmechanicallyinclinedfolkswhoaredownsizing,tobigboxhomeimprovementstoresofferingdecentdiscounts.Anddon’tbeafraidtoaskanassociatefordetailsaboutthetoolmanufacturer.Well-madetoolsalwayspayoffbyhelpingyoudoabetterjobandthey’llgiveyouyearsofreliableservice,too.Thegoodonesareoftenworthyofbeingpasseddowntothatnextbuddingsmall-engine-buffinyourfamily.

Toolsyoumaywanttopurchasetosimplifyadvancedprojectsinclude:

(A)Cylinderleakdowntester:fortestingsealingcapabilitiesofcompressioncomponents

(B)Pistonringcompressor:forcompressingringsduringassembly(C)Starterclutchwrench:forremovingandtorquingrewindstarterclutch(D)Valvelappingtool:forresurfacingvalvefacesandseats(E)Leakdowntesterclamp(F)Pluggauge:forcheckingvalveguidesforwear(G)Telescopinggauge:formeasuringinsidediametersofcylinders(H)Brakeadjustmentgauge:forsettingbandbrake(I)C-ringinstallationtool:forinstallingastartermotorc-ring(J)Pistonringexpander:forremovingandinstallingpistonrings(K)Flywheelstrapwrench:forremovingandinstallingflywheel(L)Carburetorjetscrewdrivers:forremovingandinstallingcarburetorjets(M)C-ringremovaltool:forremovingc-ringonstartermotor

(N)Torquewrench:fortighteningboltstospecified“inchpounds”oftorque(O)DCshunt:formeasuringcurrentdrawofDCmotorsandoutputofregulated

alternators

(A)Molygraphitegrease(B)Whitelithiumgrease(C)Carburetor/chokecleaner(D)Foggingoil(E)Heavy-dutysilicone(F)Batterycleaner(G)Batteryterminalprotector(H)4-uselubricant(I)Penetratingoil(J)Heavy-dutydegreaser

(K)Gasolineadditive(L)Valveguidelubricant(M)Lawnmoweroil(N)Valvelappingcompound(O)Greasegun(P)Tiresealant

SUPPLIESFORSMALL-ENGINEWORK

Togetthebestresultsfromyourrepairsandthehighestperformancefromyoursmallengine,usethelubricantsandcleanersrecommendedbyyourauthorizedservicedealeroroutdoorpowerequipmentretailer.Liketools,cleanersandlubricantsaremadeforspecificpurposes,andeachworksbestinthephysicalandchemicalenvironmentforwhichitwasintended.Substitutingoneproductforanothercouldproveineffective,damaging,orevendangerous.Yourworkwillbeeasierandmorereliablewhenyouusetherighttools,lubricants,andcleanersforthejob.Thelubricantsandcleanersshownaboverepresentthefullrangeofproductsyouneedtokeepyoursmallengineinpeakoperatingcondition.

TIP

Aninexpensivemagneticpartspick-upcomesinhandywhenyoudropsmallmetalpartsinhard-to-reachareas.

SafeSmall-EngineServicing

Youcanavoidaserioussafetyhazard—carbonmonoxide(CO)accumulation—byworkingoutdoors.COisanodorless,tasteless,poisonousgasproducedbyburninggasolineandotherfuels.Evenaninexpensivecarbonmonoxidedetectorinstalledinyourworkshop/garagecanalertyoutothepresenceofCOindoorsbeforeitreacheslethallevels.

Smallenginesburnfuelandinduceelectricity.Eachoftheseinvolvesspecialsafetyconsiderations—soyouneedtoobservetheprecautionsforboth.Keepthefollowingrulesinmind,andyouwillsimplifythejobofsafelyoperating,maintainingandrepairingyoursmallengine.

OPERATINGCONDITIONS

Ifyouneedtorunanenginetotestyourmaintenanceorrepairwork:

•Neverrunanengineindoors.•Turnofftheenginebeforeleavingthearea—evenforafewseconds.•Donotoperatetheenginenearcombustiblematerials,gasoline,orotherflammableliquids.

•Keepcombustiblematerialsawayfromthemufflerandwhereyou’vegotexposedspark(duringanignitiontest).

•Avoidrunninganengineathighspeedsorinexcessofthemanufacturer’sspecifications.

•Makesurethemufflerisinplacebeforestartingtheengine.•Pullthestartercordslowlyuntilyoufeelresistance,thenpullrapidlytostart;thishelpspreventinjurytoyourhandandarm.

•Unlesscautiouslytestingforspark,donotcranktheenginewiththesparkplugremoved;iftheengineisflooded,placethethrottleintheFASTpositionandcrankuntiltheenginestarts.

•Tostoptheengine,graduallyreduceenginespeed.Then,turnthekeytoOFFormovethecontrolstotheOFForSTOPposition.

•Whenoperatingequipmentonunimprovedlandcoveredbygrassorbrush,installasparkarrester—designedtotrapsparksdischargedfromtheengine.

•Keepequipmentflatonthegroundwhenitisoperating.Nevertiltitatasharpangle.

•Keephandsandfeetawayfrommovingorrotatingpartsontheengineorequipment.

GASOLINESAFETY

Theonlyplacewhereenginefuelandsparksshouldinteractisinthecombustionchamber.Toreducefirehazards:

•Neverlightamatchorotherflammablematerialnearanengine.•Avoidusingpowertoolsorotherequipmentthatgeneratessparkswherefuelvaporsmaybepresent.

•Allowtheenginetocoolbeforeremovingthefuelcaporfillingthetank.•Replaceafuellineorfittingifitisleakyorcracked.•Keepgasoline,solvents,andotherflammablesoutofreachofchildren.StoregasolineinUL®-approvednon-spillcontainers.Labelflammablematerialscontainersclearlyforquickidentification.For2-strokeengines,it’sreallyimportanttolabelfuelcontainerstoshowthecontent’sgas/oilratio.Thinkingyou’lleasilyrecallwhetherit’sthe1/2pintofoil-to-a-galloncontainerorone

withtheremnantsoflastseason’sethanol-regularisn’talwaysawinningguessinggame.

SAFEMAINTENANCE

Tomakesmall-enginemaintenanceandrepairtaskseasierandsafer:

•Makesureyouhaveampleworkspace,witheasyaccesstothetoolsyouneed.•Usethecorrecttoolsforeachjob.•Keepanapprovedfireextinguisherinafamiliarlocationnearyourworkarea.•Learnengineshutoffproceduressoyoucanrespondquicklyinanemergency.•Disengagethecuttingblade,wheels,orotherequipment,ifpossible,beforestartingtheengine.

•Disconnectthesparkplugwiretopreventaccidentalstartingwhenyouareservicingtheengine.

•Alwaysdisconnectthewirefromthenegativeterminalwhenservicinganelectricstartermotor.

•Checkthatasparkplugorsparkplugtesterisattachedtotheenginebeforecranking.

•Avoidcontactwithhotengineparts,suchasthemuffler,cylinderhead,orcoolingfins.

•Neverstriketheflywheelwithahammerorhardobject;itmaycausetheflywheeltoshatterduringoperation.

•Makesuretheaircleanerassemblyandblowerhousingareinplacebeforestartingtheengine.

•Removeanyfuelfromthetankandclosethefuelshutoffvalvebeforetransportinganengine.

•Useonlytheoriginalmanufacturer’sreplacementparts;anyotherpartsmaydamagetheengineandcreatesafetyhazards.

•Keepenginespeedsettingswithinmanufacturerspecifications.Higherspeedscanruintheengine.Forexample,don’trunalawnmowerengineanywherenearfullthrottleminusitsload(blade).

PROTECTINGYOURHEALTH

Fire,electricshockandasphyxiationarenottheonlydangerswhenworkingwithsmallengines.Takecaretoavoidlong-termorsuddeninjurytoyoureyes,ears,lungs,feet,andback:

•Keepyourfeet,hands,andclothingawayfrommovingengineandequipmentcomponents.

•Useeyeprotectionwhenyouworkwithenginesorpowertools.Thisprecautionisoftenignoredasparticularlyinconvenient—untilsomesmallpartortoolbreakslooseandfliesrightintoone’sirreplaceablepeepers.

•Wearearprotectiontoreducetheriskofgradualhearinglossfromexposuretoenginenoise.

•Wearafacemask,ifrequired,whenworkingwithchemicals.•Wearspeciallydesignedglovestoprotectagainstheat,harmfulchemicals,andsharpobjects,suchasmowerbladesorsnowblowertinesbeingheldfastduringremoval.

•Wearsafetyshoestoprotectagainstfallingobjects;safetyshoeshavesolesthatwon’tdeterioratewhenexposedtogasolineoroil.

•Useproperliftingtechniquesandseekhelpwithheavylifting.

FILLINGTHEFUELTANK

Spilledordrippingfuelcancauseharmtoyou,yourequipment,andtheenvironment.Youcanreducetheseoccurrencesbyusinganon-spillcanfortransportingfuelandrefueling.Whenfilling,placeyourfuelcanorpowerequipmentontheground—awayfromappliances,heaters,andothersourcesofflameorheat.Neverfillyourcanorrefuelyourequipmentwhileeitheroneisinsideatrunkoronatruckbed.Duringtransport,fuelshouldbeinasecure,uprightpositionandtightlysealed.Provideampleventilationtopreventfumesfrombuildingupinthepassengercompartmentortrunk,wherestaticelectricitycouldignitegasfumes.

MotorMedicalSchool101

Sometimesthebestwaytoexplaininformationiswithastory.Thisisastrueof

small-enginerepairasitistrueofanthropologyormilitaryhistory—well,maybenotastrue,butmyyearsofteachinghaveshownmethatifyouwanttocatchyourstudents’attention,tellthemastory.Sohereitgoes:Ericheardthemotoronhisrecentlypurchasedsnowblowerjustkindofthinout,makesomelaboredchugs,andthendie.Theback-savingbutexpensivepieceofpowerequipmenthadonlyafewminutesonitsclockwhenitwentsilentafterclearingabouteightfeetofdriveway.FranticallypushingonthefuelprimerbulbandthenyankingonthestartercordadozenincreasinglyaggravatingtimesdidnothingbutaddtoEric’sfast-growingfearthathe’dbeenstuckwithalemoninthemidstofawhite-outblizzard.“Whatisthematterwiththisdarnthing?”heyelledoutintothecoldair.Therewasplentyofgasinthetank,andtheengine’slittledipstickshowedenoughoil,too.AneighborknownforhermechanicalacumennoticedEric’sdilemma.Shewalkedtowardthesilentsnowblowertotakealookandtrytohelp.Visually,sheagreed,everythingappearedtobeinproperorder…butnothingEricconsultedintheowner’smanualandnothingtheneighbortinkeredwithproducedasinglepop.Evenatesttheneighborconductedonthemotor’signitionsystemruledoutproblemswiththesparkplug.Ericwasreadytogiveupwhenhisneighbornoticedsomethingthatcausedhertoshakeherheadandsmile.SomeoneatthefactoryhadmisappliedthetinyfuelvalvedecaltotheplasticshroudinginsuchawaythatwhatlookedtobeONwasactuallyOFF.“Don’tfeelsobad,”Eric’sengineexpertsuggestedtoldhimwhenthequickfixhadtheenginerunning,“Ialmostmissedthatquickfixmyself!”

—PeterHunn

Thedetailsofthisstoryandthespecificproblemtheydiscoveredarelessimportantthanthebroaderlessonlearned:alwayscheckthesimplestpossibilitiesfirst.

LearningHowtoDiagnoseaMotor’sSymptomsSmall-enginerepairprojectsshouldalwaysstartwiththisbrandoftroubleshooting—thesearchforthesourceofaproblem—beginningwiththemostobviousorsimpleexplanationandworkingtowardthelessobviousormorecomplex.

Whenyou’retroubleshootingasmall-engineproblem,youcangainconfidencebybeingabletoruleout,onebyonethroughtheprocessofelimination,variouspartsorsystemsaspossiblesourcesoftheproblem.Forexample,ifyourweed-whackerstopsonitsownafterabouttwenty-seconds,evenanovicemechaniccouldsafelycrossoffthecarryinghandleasbeingtheculprit;Onedown,severalmoretogo.It’simportanttoworksystematicallytoisolatethecauseratherthanforeverskippingpartsorsystemsthathavenevergivenyouanyreasontobelieveareactingup.Thisforensicdiagnosisprocessisalotlikelookingforalostsetofkeys:often,they’reinan“obvious”placethatdidn’tseemworthcheckingduringmuchofthetimespentinthatfranticsearch.Thesolutionisnottooverlookthingsthatmayotherwiseseemtooeasyafixtobetrue.Theyjustmightholdthekeystoenjoyinganewlyrecuperatedengine.

THE“DIAGNOSTICTRIPLET”QUESTIONS:

Areyouhearingstrangesounds?Isanythingleaking?Arethereanysmokyclues?

Thethreequeriesaboveshouldbeconsideredbeforeyoueverreachforascrewdriverorwrench.

Areyouhearingstrangesounds?Iftheenginecanstart,doesitmakeanyunusualnoises?Whilethere’snoneedtryingtomimicafunnyclangorknock,itishelpfultobeginrecognizingsoundsthatwillhelpyoupinpointamechanicalproblem.Ifthemotorissadlysilentandabsolutelynothingmoveswhenyouattempttoengagethestarter,thatsometimesindicatesaserioustechnicaldifficulty,butnotalways.So,don’tstartworrying,yet.

Isanythingleaking?Lookforleakson,under,andaroundtheengineanditspowerequipmenthost.Fuel,oil,grease,andwateraretheusualsuspectshere.Notewherethey’recomingfromandwhetherornotthey’restillflowingoroozing.Discoveringthe“headwaters”sourceofaleak,andnotjustwherethecollectivedripsendedup,canbeaninvaluabletroubleshootingbreakthrough.Alsoinspectvisuallyforcracksinthehosesandmetal.Quitepossibly,alooselamporfittingisallowingtheleak.

Arethereanysmokyclues?Ifyouareabletooperatetheengine,isitbelchinganyunusualquantitiesorparticularcolorsofsmoke?Doestherateofspeedincreaseorlessenthissmoke?Isitworseorcleareraftertheenginewarmsupforafewminutes?Tomatchyouranswerswithpossiblecauses,seepage40.

•Lookfortheoverallcause,notjustatemporarycureforthesymptoms.•Gatherandjotdownasmuchinformationaspossible.Knowingwhetheranenginewasattopspeedwhenitstoppedrunningorwhetheritsimplyfailedtostartmaymakeadifferencewhenyou’retryingtoidentifytheproblem.Rememberthe“diagnostictripletquestions”above.Alsorealizethatasimplesolutionmightnotalwaysbringthemotorbacktofactoryfreshnessorsolvetheengine’soverallhealthissues,someofwhichwillbeclearerafterarrivingatoneofthedifficulties.Forexample,replacingabadsparkplugmaygetan

enginerunningagain,buttherealculpritmaybeadirtycarburetororificeforwhichthenewplugwasabletosufficientlycompensateinordertogetthemotorfiringforawhileanyway.

COMMONPROBLEMSATAGLANCE

Problem:Enginewon’tstart

Fuellineproblems—Formoreinformation,gotopage38

Carburetorproblems—Formoreinformation,gotopage38

Ignitionproblems—Formoreinformation,gotopage39

Compressionproblems—Formoreinformation,gotopage39

Problem:Enginerunspoorly

Enginesmokes—Formoreinformation,gotopage40

Engineoverheats—Formoreinformation,gotopage40

Engineknocks—Formoreinformation,gotopage41

Sparkplugmissesunderload—Formoreinformation,gotopage41

TROUBLESHOOTINGGUIDEIfthisistheproblem: Engine/flywheelwon’trotate

Askthisquestion: Isthestarterjammedorrewindbroken?Iftheanswerisyes: Removerewind/shroudandtryrotatingflywheel.Ifitdoesso

freely,therewindneedsattention.Askthisquestion: Isthemowerblade(orequivalent)hittingsomething?Iftheanswerisyes: Freetheoffendingobstruction.Askthisquestion: Istheengineorbladebrakeactivated?Iftheanswerisyes: Disengageit.Askthisquestion: Isanenginebearingseized?Iftheanswerisyes: Typically,theenginemustbedisassembledtodeterminethis.Askthisquestion: Isthepistonstuckinthecylinder?Iftheanswerisyes: Apiston“stuck”fromlengthysittingcanoftenbecoaxedfree

bysquirtingthecylinder—throughthesparkplughole—withpenetratingoilorkerosene,lettingitworkforadayorso,andthenmovingtheflywheelbitbybit,untilthepistonfreelymoveswithinthecylinder.

Askthisquestion: Isthecrankshaftbent?Iftheanswerisyes: Thisrequiresmajordisassemblyandattentionbyawell-

equippedshop.

Ifthisistheproblem: Enginewon’tstart(Fuelline)

Askthisquestion: Isthefueltankempty?Iftheanswerisyes: Fillthefueltank;iftheengineisstillhot,waituntilithas

cooledbeforefillingthetank(see“HowtoRemoveandCleantheFuelTank,”page74).

Askthisquestion: Istheshut-offvalveclosed?Iftheanswerisyes: Openthefuelshut-offvalve(see“HowtoRemoveandClean

theFuelTank,”page74).Askthisquestion: Isthefueldilutedwithwater?Iftheanswerisyes: Emptythetank,replacethefuelandcheckforleaksinthefuel

tankcap(see“HowtoRemoveandCleantheFuelTank,”page74).

Askthisquestion: Isthefuellineorinletscreenblocked?Iftheanswerisyes: Disconnecttheinletscreenfromtheengineandcleanit,using

compressedair.NOTE:Donotusecompressedairneartheengine(see“HowtoRemoveandCleantheFuelTank,”page74).

Askthisquestion: Isthefueltankcapcloggedorunvented?Iftheanswerisyes: Makesurethecapisventedandthatairholesarenotclogged

(see“HowtoRemoveandCleantheFuelTank,”page74).(Carburetor)

Askthisquestion: Isthecarburetorblocked?Iftheanswerisyes: Removethesparkplugleadandsparkplug;pourateaspoonof

fueldirectlyintothecylinder;reinsertthesparkplugandlead;starttheengine;ifitrunsforamomentbeforequitting,overhaulthecarburetor(seeAdjustingtheCarburetor,”pages82and100).

Askthisquestion: Istheengineflooded?Iftheanswerisyes: Adjustthefloatinthefuelbowl,ifadjustable;makesurethe

chokeisnotsettoohigh(seeinformationonadjustingoroverhaulingthecarburetoronpages82and100).

Ifthisistheproblem: Enginewon’tstart(Ignition)

Askthisquestion: Isthesparkplugfouled?Iftheanswerisyes: Removethesparkplug;cleanthecontactsorreplacetheplug

(see“ServicingSparkPlugs,”pages52to53).Askthisquestion: Isthesparkpluggapsetincorrectly?Iftheanswerisyes: Removethesparkplug;resetthegap(see“ServicingSpark

Plugs,”pages52to53).Askthisquestion: Isthesparkplugleadfaulty?Iftheanswerisyes: Testtheleadwithasparktester,thentesttheengine(see

“ServicingSparkPlugs,”pages52to53).Askthisquestion: Isthekillswitchshorted?Iftheanswerisyes: Repairorreplacethekillswitch(see“ServicingtheBrake,”

pages132to137).Askthisquestion: Istheflywheelkeydamaged?Iftheanswerisyes: Replacetheflywheelkey,re-torquetheflywheelnuttoproper

specifications,thentrytostarttheengine;ifitstillwon’tstart,checktheignitionarmature,wireconnectionsor,insomeengines,thepoints(see“ReplacingtheIgnition,”pages110to113).

(Compression)

Askthisquestion: Ina4-stroke,arethevalves,piston,cylinderorconnectingroddamaged?

Iftheanswerisyes: Performacompressiontest(Onanysmallengine,compressiongaugeshouldread80psiormorewhenthestartercordispulledvigorously;ifthetestindicatespoorcompression,inspectthevalves,pistonandcylinderfordamageandrepairthemasneeded(see“RemovingCarbonDeposits,”pages118to121,and“ServicingtheValves,”pages122to131).

Askthisquestion: Ifa2-stroke,areallofthecrankcasesealsintact?Iftheanswerisyes: Ifno,replaceseals.Askthisquestion: Isthereedvalveworkingproperly?Iftheanswerisyes: Ifno,replacereedvalve.Askthisquestion: Anylooseboltsoncrankcase,carburetormount?Iftheanswerisyes: Tightenbolts.Askthisquestion: Anybadgasketsallowingairin/out?Iftheanswerisyes: Replacegasket.

Ifthisistheproblem: Enginerunspoorly(Enginesmokes)

Askthisquestion: Isthesmokewhite?Iftheanswerisyes: Checkforwater(orcoolant,ifradiator-equipped)infueltank,

line,carburetor,orcylinder.Askthisquestion: Isthesmokeblue?Iftheanswerisyes: Indicatesexcessiveoilisbeingburned.Checktoseeifpiston

ringsarewornorstuck.Possiblevalveissueon4-stroke.Possiblytoomuchoilmixedinthegasoline,if2-strokeengine.

Askthisquestion: Isthesmokeblack?Iftheanswerisyes: Asignthatengineisrunningrich(toomuchfuelinthefuel/air

ratio).Carburetorneedsadjusting.Askthisquestion: Isthefuelmixturetoorich?Iftheanswerisyes: Adjustthecarburetor(see“AdjustingtheCarburetor,”page

82).Askthisquestion: Istheairfilterplugged?Iftheanswerisyes: Cleanorreplacetheaircleaner(see“ServicingAirCleaners,”

pages54to57).(Engineoverheats)

Askthisquestion: Istheenginedirty?Iftheanswerisyes: Cleantheengine(see“RemovingDebris,”pages69to71).Askthisquestion: Istheoillevellow(ina4-strokeenginecrankcase)?Iftheanswerisyes: Addoiltotheengineoilfill.NOTE:Neveraddoiltothe

gasolinefora4-strokeengine(see“Checking&ChangingOil,”pages48to51).

Askthisquestion: Istheretoolittle,orexcessiveoilmixedwiththegasinthe2-strokeengine?

Iftheanswerisyes: Dumpexistingfuelandreintroduceafreshgas/2-cycleoilmix,accordingtothemanufacturer’sspecifications.

Askthisquestion: Areanyshroudsorcoolingfinsmissingorbroken?Iftheanswerisyes: Installnewpartsasneeded(seeadditionaltools,parts,and

supplies,pages28to31).Askthisquestion: Isthefuelmixturetoolean?Iftheanswerisyes: Adjustthecarburetor(see“AdjustingtheCarburetor,”page

82).Askthisquestion: Istherealeakygasket?Iftheanswerisyes: Replacethegasket(see“OverhaulingtheCarburetor,”page

100).Askthisquestion: Ona2-stroke,isthereanycrankcaseleakage?Iftheanswerisyes: Checkseals,gasketcondition,tightenbolts.Askthisquestion: Isthefueltankventorfueltankscreenplugged?Iftheanswerisyes: Cleanthefueltankventandfueltankscreen(see“Removing

andServicingtheFuelTank,”pages73to74).

Ifthisistheproblem: Enginerunspoorly(Engineknocks)

Askthisquestion: Doesthenoisegetlouder(asthemotorwarmsup)andchangepitchwhentheenginespeedisincreased?

Iftheanswerisyes: Thisisprobablyaconnectingrodknockrequiringnewconnectingrod/rodendcapand/orbearings.

Askthisquestion: Isthereaquickdoubleknockespeciallynoticeableatslowspeeds?

Iftheanswerisyes: Here,alooselyfittingpistonpin(holdingthepistonontothetopoftheconnectingrod)isthelikelysuspect.Itcouldalsosignalexcessivewearinthepistonpinholeoralooselyfittingconnectingrod.Replacementpartsareneeded.

Askthisquestion: Isthereaknockthatisnoisierthanarodknock,butseemstosoftenasthemotorrunsawhile?

Iftheanswerisyes: Perhaps“pistonslap”istheissue.Awornpistonring,cylinderwall,and/orpistonisallowingthepistontofitinthecylindermorelooselythandesignedforoptimumclearance/compression.Replacementpartsareneeded.

Askthisquestion: Doesthecombustionchambercontainexcesscarbon?Iftheanswerisyes: Cleancarbonfromthepistonandhead(see“RemovingCarbon

Deposits,”pages118to121).Askthisquestion: Istheflywheelloose?Iftheanswerisyes: Inspecttheflywheelandkey;replaceasneeded(see

“InspectingtheFlywheel&Key,”pages108to109).(Sparkplugmissesunderload)

Askthisquestion: Isthesparkplugfouled?Iftheanswerisyes: Cleanthesparkplug(see“CleaningandInspectingaSpark

Plug,”page52–53).Ifpluglooks/worksOK,checkconditionofignitionwiring,especiallyplugleadwireandconnectionatendofleadwirewhereitattachestosparkplug.

Askthisquestion: Isthesparkplugfaultyorgapincorrect?Iftheanswerisyes: Replacethesparkplugoradjustthesparkpluggap(see

“CleaningandInspectingaSparkPlug,”page52–53).Askthisquestion: Arethebreakerpointsfaulty?Iftheanswerisyes: Installasolid-stateignition(see“ReplacingtheIgnition,”

pages110to113).Askthisquestion: Isthecarburetorsetincorrectly?Iftheanswerisyes: Adjustthecarburetor(see“AdjustingtheCarburetor,”page

82).Askthisquestion: Ona4-strokeengine,isthevalvespringweak?Iftheanswerisyes: Replacethevalvespring(see“ServicingtheValves,”pages122

to131).Askthisquestion: Ona4-strokeengine,isthevalveclearancesetincorrectly?Iftheanswerisyes: Adjustthevalveclearancetorecommendedsettings(see

“ServicingtheValves,”pages122to131).

EasyButImportantMaintenance

Oursmall-enginerepairstorycontinues(seepage35).Ericalwaysthoughtitrathercuriousthattheguyacrossthestreetcutgrass

withanancient2-strokelawnmowerfromtheKennedyera.Afterall,thefellowandhiswifedidn’tappeartobefiscallydowntrodden.Whenthecouplewalkedpasthisdrivewayoneearlysummereveningpushingarusty,squeaky,rattlythingwithjustenoughdecalremainingtoidentifyitasaLAWN-BOYmower,Ericcouldn’tresistengagingtheduoinsomeinvestigativeconversation.BeforeErichadfinishedanintroductorywave,theguypointedtohissmilingspouseandapologized,“Sorryfordisturbingtheneighborhoodpeace!Mymotorheadwifeheresawthismoweratsomebody’scurb,anddecidedtotakepityonthepooroldthing;Likeotherwomenmightdoforastraypuppy.”Sheagreedandnotedherlatestacquisitionwasevenmorevintagethantheoneshe’drescuedandrestoredandnowused.“Where’dyoulearnhowtofixthesethings?”Ericasked.“IguessyoucouldsayIwasrecruitedintoatrainingprogrambyasmall-

engineshop,”shesmiled;“Averysmallsmall-engineshop.Theownertaughtmethatanyonecanrepairsmallenginesaslongasshe—orhe—hasasystemandisdisciplinedenoughtofollowit.Anyway,mostpeopleonlyruntheirpowerequipmentforanhourortwoaweek,andthenforonlypartoftheyear.Iguessyoucouldsaythattheaveragesmallenginesuffersmuchmorefromneglectthanfrombeingused.”

—P.H.

Itisalwaysagoodideatoreadthroughtheowner’smanualcovertocoverwhenyouacquireanewpieceofequipment.Butbesuretokeepithandyinaconvenientspotfortimeswhenyouneedtorefertoitforspecificinformation.Ifyouloseyourmanual,orneverhadoneinthefirstplace,therearemanywebsiteswhereyoucansearchfor,locate,anddownloadelectronicfilesoftheoriginalowner’smanuals—sometimesfornocost.

REGULARMAINTENANCESCHEDULE

Youcanavoidmanysmallengineproblemsandsavemoneyonparts,repairs,and/orapriceynewpieceofpowerequipmentifyoufollowaregularmaintenanceschedule.Makeroutinemaintenanceahabitwhenyourengineisnewandalwaysconsultyourowner’smanualforspecialguidelinesforyourparticularmotor.It’ssmarttoserviceyourenginemorefrequentlyifyouuseitheavilyorunderdustyordirtyconditions.

AFTERTHEFIRSTFIVEHOURSOFUSE:

•Changetheoilandfilter(pages48to51).

AFTEREACHUSE:

•Checktheoil(page49).•Removedebrisfromcylindercoolingfins,aswellasaroundthefueltankandmuffler(pages69,70,74,94,and95).

EVERY25HOURSOREVERYSEASON:

•Changetheoilifoperatingunderheavyloadorinhotweather(pages48to51).

•Servicetheaircleanerassembly(pages54to57).•Cleanthefueltankandline(page74).•Cleanthecarburetorfloatbowl,ifequipped(page82).•Inspecttherewindropeforwear(pages90to91).•Cleanthecoolingfinsontheengineblock(pages69to71).•Removedebrisfromtheblowerhousing(pages69to71).•Checkenginecompression(page58).•Inspectgovernorspringsandlinkages(pages86to89).•Inspectignitionarmatureandwires(pages110to113).•Inspectthemuffler(pages92to95).•Checkthevalvetappetclearances(pages126to127).

•Replacethesparkplug(pages52to53).•Adjustthecarburetor(page82).•Checktheenginemountingbolts/nuts(page59).

EVERY100HOURSOREVERYSEASON:

•Thoroughlycleanthecoolingsystem(pages69to71).•Changetheoilfilter,ifequipped(page50).•Decarbonizethecylinderhead(pages118to121).

*Cleanmoreofteniftheengineoperatesunderdustyconditionsorintall,drygrass.

End-of-seasonmaintenanceEnginesarebuilttorun.Butmanysmallenginesareonlyusedseasonallyandsitidleforlongperiods.Long-termstoragecanaggravateoverlookedproblems,andotherproblemscandevelop.Forexample,unstabilizedgasleftinanenginecangumupacarburetor,unlubricatedenginepartscancorrode,andmoisturecanaccumulateintheignitionsystem.Withproperstoragepreparation,youcanavoidmostsuchproblems.

Ifyouplantostoreyourengineformorethanthirtydays:

DrainthegasolineGasolinethat’sallowedtostandforoveramonthmayformavarnishontheinsideofthefueltank,carburetorandotherfuelsystemcomponents.Drainingthegasolinereducesvarnishproblems.Anotherwaytoprotectagainstthevarnishingeffectsofoldfuelistoaddagasolinestabilizertoyourfuel,beforestorage(page45).Whenyou’redonewithyoursmallengine’s

finalchorefortheseasonandarereadytoturnitoff,dosobyclosingthefuelvalveandrunningitoutofgas.Drainthecarburetorfloatbowl(ifequipped)aswell.TheEnvironmentalProtectionAgencyrecommendsaddingthedrainedgasolinetoyourcar’sgastank,providedyourcartankisfairlyfull.Oncediluted,oldgasolinewillnotharmyourcarengine.

Changetheoil(4-Strokeonly)Changingtheoilwillpreventparticlesofdirtintheoilfromadheringtoengineparts(pages48to51).

SealthefuelcapYoursmallengineemitssmallamountsoffuelvaporintotheair—evenwhenit’snotrunning.Toreduceemissionsduringstorage,covertheventedfuelcapwithaluminumfoilandsecureitwithanelasticband.

LubricateinternalpartsInjectingoilthroughthesparkplugholeisaneasywaytolubricatethecylinder.Justsquirtabout1/2ounceoffoggingoil(orsomemotoroil)intothesparkplughole.Then,spreaditthroughoutthecylinderbyreattachingthesparkplugandveryslowlypullingtherewind.

InspectthesparkplugCleanandregapthesparkplugorreplaceit,asnecessary(pages52to53).

ServicetheaircleanerThisstepcanextendthelifeoftheaircleanerandimproveengineperformancenextseason(pages54to57).

SealthecombustionchamberYoucanpreventvarnishformationinthecombustionchamberduringstoragebyplacingthepistonattopdeadcenter(TDC),thepointatwhichbothvalves(ina4-strokeengine)areclosed.Thiskeepsoutstalefuelanddebris.Justpulltherewindropeslowly.Whenyoufeelincreasedtensionontherope(duetothecompressionofairinthechamber),thepistonisatTDC(page14).Ifyourmachinehasa2-strokeengine,slowlypullthestartercorduntilyoufeelthecompressionincreasing,indicatingthepistonhascoveredthecylinderports.

RemovedirtanddebristhencoverDebristendstoaccumulateinthecylinderheadfins,undertheblowerhousingandaroundthemuffler.Thisdebriscanfallintotheengine.Removeitnowtoensuregoodperformancenextseason.Then,covertheenginewithasheetofplasticandstoreinadryplace.Beawarethatcritters,suchasmice,getchillyandlookforsmallopenings(onmufflers,carburetorairintakes,andundershrouding)inwhichtobuildtheirnests.Theirwastecanreallymakeacorrosivemess!Checkfornew“tenants”periodically.

Checking&ChangingOilona4-Stroke

Collectusedengineoilinaplasticcontainerthatcanbesealedsecurelyandthendisposeofitpromptly,usuallybybringingittoaservicestationortoarecyclingfacilitythatacceptsoil.

Whenyoupourfreshoilintothecrankcase,it’sagoldenorambercolor.Gradually,theheat,dirtparticles,andagitatedairinthecrankcasecausetheoiltodarken.Darkoilisnotonlydirty;ithasalsolostmuchofitsabilitytocoatandprotectenginecomponents.Manufacturersrecommendchangingtheoilinyoursmallengineafterevery25hoursofoperation.Foranewengine,you’llalsoneedtochangetheoilafterthefirstfivehoursofoperation.Newenginesrequirethisextrasteptoflushoutsmallparticlesthataccumulatenaturallyduringthebreak-inperiod.

Hoursofusearejustonefactorindetermininghowoftentheoilshouldbechanged;theamountofwearandtearisequallyimportant.Justliketheoilinapickuptruckoperatedinextremelydirtyordustyconditionsorathighspeeds,theoilinalawnmowerorothersmallenginebreaksdownfasterundertough

conditions,suchaswetgrass,heavydust,hightemperatures,androughorhillyterrain.

Donotoverfillyourcrankcase.Toomuchoilcancausethesametypeofenginedamageasnothavingenough.Airbubblesformintheoil,reducingoveralllubrication.Theresultingfrictionandmetal-to-metalcontactcancauseprematurepartfailure.Excessoilcanalsoburninthecylinder,producingsmokeandleavingcarbondeposits.

Tools&Materials

•Socketwrenchset,boxwrench,oradjustablewrench•Screwdriverorhexkey•Oilfilterorpipewrench(formodelswithfilters)•Oildrainpan•Funnel

Timerequired:30minutes

Thissectioncoversproceduresforcheckingandchangingoilandoilfilters,andofferstipsonavoidingspillsandchoosingtherightoilandotherproductsforyourengine.

Gettingtheoldoiloutofyououtdoorpowerequipmentcanbetricky,especiallywithtoolslikelawnmowerswhereyouhavetotipthemachinetogetaccesstothedraintheplug.Trytodothiswhenthegastankisemptyornearlyemptytominimizelossoffuelthroughtheventinthegascap.Andtomaximizetheamountofparticulatematteryouremovewiththeoldoil,runtheengineforacoupleofminutesrightbeforedrainingtheoilsodebrisdoesnotsettle.

CHECKINGTHEOILONA4-STROKEENGINE

Makeitahabittochecktheoillevelandappearanceeachtimeyou’reabouttostartasmallengine.Checkingtheoilwhiletheengineiscoldandmostoftheoilisinthecrankcaseyieldsthemostaccuratereading.Youwon’tneedtochangeoraddoileverytime.Butyou’llensureabetter-runningengineandavoidproblemsdowntheroadifyoukeepthecrankcasefullandchangetheoilonscheduleandanytimetheoillosesitsamberhue.Morethanafewoilfill/draincapshave

vibratedoffofmowersandsnowblowerswithoutpromptownerdetection.

Howtochecktheoilona4-stroke

1.Startbylocatingtheoilfillcaponthecrankcase.Fillcaplocationsvary,dependingonthemakeandmodelofyourengine.Onnewermodels,lookforanoil-cansymbolortheword“oil”or“fill”stampedontheplug.Onsmalltractors,youmayhavetoliftthehoodtolocatethiscap.Someenginescontaineitheranextendedoilfilltubeorastandardfillholewithadipstickforinspection.Othersrequireyoutoremovethefillcaptocheckthattheoilisatthefilllineorthetopofthefillhole.

2.Topreventdirtanddebrisfromfallingintothecrankcase,wipetheareaaroundthecapwithacleanclothbeforeremovingthecap.Ifthereisnodipstick,dabtheoilwithacleantipoftheclothtoinspecttheoil.

3.Iftheengineincludesadipstickcap,removethedipstickandwipeitwithacleancloth.Toensureanaccuratereading,reinsertthedipstickcompletely.Then,removeitagainandchecktheoillevel.Ifthedipstickcapisascrewintype,ensureanaccuratereadingbyscrewingitinallthewaybeforeremovingitasecondtimetocheckthelevel.Theoilmarkonthedipstickshouldbebetweenthelinesshownonthedipstick.ItshouldneverbeabovetheFULLlineorbelowtheADDline.

CHANGINGTHEOILONA4-STROKEENGINE

Onceyoudecidetheoilneedschanging,checkyourowner’smanualtodeterminethetypeofoil,andmakesureyouhaveenoughonhand.Then,runtheengineforseveralminutes.Drainingtheoilwhileit’swarmwillcarryoffmanyfloatingparticlesthatwouldotherwisesettleintheengine.

Howtochangetheoilona4-stroke

1.Stoptheengine,disconnectthesparkpluglead,andsecureitawayfromthesparkplug.Tiltthemowerdeckandpositionsomenewspaperandanoilpanorjugbeneaththemower.Then,locatetheoildrainplug(photobelow).Onmowers,theplugistypicallybelowthedeckandmaybeobscuredbyalayerofgrassanddebris.Wipetheareawitharagtopreventdebrisfromfallingintothecrankcasewhenyouopenthedrainplug.Useasocketwrenchtoturntheplugcounterclockwise,allowingtheoldoiltodrain.Iftheplugalsoservesasafillcap,itmayhavetwoprongssoyoucanloosenitbyhandoruseascrewdriverorhexkeyforadditionaltorque.Replacethedrainplugbytwistingclockwiseandtighteningwithaboxwrenchoradjustablewrench.

2.Ifyourenginehasafilter,replacethefilteratleastonceaseason,moreoftenunderheavyuse(see“RegularMaintenance,”page44).Replacethefilterbytwistingcounterclockwiseonthebody,usingafilterwrenchorpipewrench.Lightlyoilthefiltergasketwithcleanengineoil.Installanewfilterratedforyourengine.Screwinthefilterbyhanduntilthegasketcontactsthefilteradapter.Tightenthefilteranadditional1/2to3/4turn.

3.Addtheappropriatequantityofoil(seeyourowner’smanual).Then,runtheengineatidleandcheckforleaks.Afteranoilchange,disposeofoilandsoiledragsinaccordancewithlocalenvironmentalstatutes.Inmanyareas,oilcanbeleftatcurbsidewithotherrecyclables,provideditissealedinarecyclablecontainer.Checktheregulationsinyourarea.

Afewofthemorepopulargradesofengineoilformulatedespeciallyforsmallengines.Seedescriptionsbelow.

CHOOSETHEPROPEROIL

(A)100percentSyntheticOil.Uniquelyblendedforuseinall4-strokeengines,all-seasonoilprovidestheextraprotectionneededinthemostsevereoperatingconditions.Itexhibitsexcellentcold-weatherflowcharacteristicsthatminimizeenginewearandprovideeasiercoldstarting.

(B)2-cycleengineoil.Productshowncontainsfuelstabilizer,asitisaddeddirectlytothefuel.

(C)Marine-grade2-cycleengineoilisusedwithoutboards,motorcycles,snowmobilesandotheroutdoorpowerequipmentthathasa2-strokeengine.

(D)Small-engineoilisformulatedtolubricateall4-cyclesengines,includingthoseforlawnmowers,generators,pressurewashersandothertypesofoutdoorpowerequipment.

TIP

Anautomotivefunnelhasanextra-longnecktomakeiteasiertodeliverfreshoiltoyoursmallenginewithoutanyspillage.

ServicingSparkPlugs

Asparkplugsocketisrequiredfortighteningandlooseningsparkplugs,butoncetheyarespinningyoucanusuallyremovethembyhand.Sparkplugsizesandratingsvaryquiteabit—besuretheplugsyoubuyarethecorrectonesforyourengine—mostpartsdealershavechartsandspecbookswiththisinformation.

Theelectrodesonasparkplugmustbecleanandsharptoproducethepowerfulsparkrequiredforignition.Themorewornordirtyasparkplug,themorevoltage—andthegreaterthetugontherewind—requiredtoproduceanadequatespark.

Ifyouhaven’ttunedyourenginerecentlyandhavetoyankrepeatedlyontherewindtostarttheengine,adamagedsparkplugmaybetheculprit.Inconsistentfiring,knownasspark“miss,”canresultinsluggishengineoperationandpooracceleration.Adamagedsparkplugmayalsocauseexcessivefuelconsumption,depositsonthecylinderhead,andoildilution.

Luckily,asparkplugisoneoftheeasiestenginecomponentstorepairandan

inexpensiveonetoreplace.Andyourstandardsocketsetmayalreadyincludethemostimportanttool—asparkplugwrench.

Thissectioncoverstheessentialsofsparkpluginspectionandreplacement.Itshowsyouhowtouseasparktesterandhowtoadjustandcleanasparkplugthatiswornbutstillserviceable.Justremember,youcan’tgowrongbyreplacingit.

Tools&Materials

•Sparktester•Sparkplugsocket(sizesvary)•Socketwrench•Wirebrush•Plug/pointcleaner•Sparkpluggauge

Timerequired:15minutes

CLEANINGANDINSPECTINGASPARKPLUG

1.Disconnectthesparkpluglead.Then,cleantheareaaroundthesparkplugtoavoidgettingdebrisinthecombustionchamberwhenyouremovetheplug.

2.Removethesparkplugusingasparkplugsocket.

3.Cleanlightdepositsfromtheplugwithawirebrushandspray-onplugcleaner.Then,useasturdyknifeifnecessarytoscrapeofftoughdeposits.NOTE:Nevercleanasparkplugwithashotblasterorabrasives.

4.Inspectthesparkplugforverystubborndeposits,orforcrackedporcelainorelectrodesthathavebeenburnedaway.Ifanyoftheseconditionsexists,replacethesparkplug.

5.Useasparkpluggaugetomeasurethegapbetweenthetwoelectrodes(onestraight,onecurved)atthetipofyoursparkplug(photoA).Manysmallenginesrequirea.030inchgap.Checkthespecificationsforyourmodelwithyourpowerequipmentdealer.Ifnecessary,useasparkpluggaugetoadjustthegapbygentlybendingthecurvedelectrode.Whenthegapiscorrect,thegaugewilldragslightlyasyoupullitthroughthegap.

6.Reinstalltheplug,takingcarenottoovertighten.Then,attachthesparkpluglead.

CHECKINGIGNITIONWITHASPARKTESTER

Asparktesteroffersaninexpensive,easywaytodiagnoseignitionproblems(see“CheckingforSparkMiss,”below).

Ifyoufindaproblem,removeandinspectthesparkplug.Replacethesparkplugifyoufindevidenceofwearorburningatthesparkplugtip.Sparkplugsareinexpensiveandanewonemaysolvetheproblem.

1.Connectthesparkplugleadtothelongterminalofyourtesterandgroundthetestertotheenginewiththetester’salligatorclip.

2.Usetherewindorelectricstartertocranktheengine,andlookforasparkinthetester’swindow.

3.Ifyouseeasparkjumpthegapinthetester,theignitionisfunctioning.Theabsenceofavisiblesparkindicatesaproblemintheignitionsystem.

CHECKINGFORSPARKMISS

Asparkplugthatisfouledorimproperlygappedmaynotallowsparkstojumpthegapbetweenelectrodesconsistently.Thesparkplugwillfireerraticallyor

mayoccasionallyfailtospark.Testforthisproblem—knownasspark“miss”—ifyourenginestumbles,withanoticeabledecreaseinenginesound.Sparkmisscanalsocausetheenginetoemitblacksmokeorapoppingsound,asunburnedfuelexitswiththeexhaustandignitesinsidethemuffler.

1.Withthesparkpugscrewedintothecylinderhead,attachthesparkplugleadtothelongterminalofthesparktester.Attachthetster’salligatorcliptothesparkplug(photoC).

2.Starttheengineandwatchthetester’ssparkgap.You’llrecognizesparkmissbytheuneventimingofthesparksinthetester.

ServicingAirCleanersAproperlymaintainedaircleanerisyourengine’sfirstlineofdefenseagainstthedestructiveeffectsofdirt.Whentheaircleanerisingoodcondition,itkeepsairbornedirtparticlesfromenteringthroughthecarburetor.Iftheaircleanerisnotmaintained,dirtanddustwillgraduallymaketheirwayintotheengine.Anddon’tunderestimatedirt’spotentialtocausedamage.Itcanleadtoasharpdropinenginepower,or,worse,causeprematurewearofcriticalenginecomponents.

Theaircleanerfiltersintakeaironitswaytothecombustionchamberandmustbecleanedorreplacedwhenitbecomesdirtyorclogged.

Manytypesofaircleanersareusedinsmallengines.Mostcontainafoamorpleated-paperelement.

Dual-elementaircleanerscontainapleated-paperelementwithafoamprecleaner,offeringtwolayersofprotection.Discardthepaperelementwhenyoucannolongerremovedirtfromthepleatsbytappingtheelementonahard,drysurface.Youmaybeabletowashandreusethefoamprecleaner.Foam

elementscanbecleanedwithhotwaterandliquiddishdetergentthatcontainsagrease-cuttingagent.

Single-elementaircleanersshouldbeservicedevery25hours(oronceaseason).Inadual-elementsystem,theprecleanershouldbecleanedevery25hours.Thecartridgeshouldbecleanedevery100hours.Refertothephoto(opposite)toidentifytheaircleaneronyourengine.

Tools&Materials

•Engineoil•Screwdrivers•Liquiddetergent

Timerequired:30minutes

COMMONAIRCLEANERS

Somesmall-engineaircleanerscontainanoiled-foamelement,othersthepleated-papercartridge.Newerenginesoftencontainacombinationofthetwo.Dual-elementdesignsconsistofapleated-papercartridgeandafoamprecleaner.Someprecleanersaredesignedtobeoiled.Ameshbackingseparatestheoilontheprecleanerfromthesurfaceofthepaperelement.Othersread“Donotoil.”Identifythetypeofaircleaneronyourenginebeforecleaning.

Don’twaituntilyouraircleanerelementlookslikethistoreplaceit.Ifyourelementhasbecomepermanentlydiscoloredorhasbeguntobreakdownortear,extendthelifeofyoursmallenginebyinstallinganewone.

Pleatsinapaperelementthatarediscolored,bentorwater-damagedcannolongerprovideadequateairtothecarburetor.Replacetheelementwhenitapproachesthiscondition.

HowtoServiceaFoamAirCleaner

1.Loosenthescrewsorwingnutsthatholdtheaircleanerassemblyinplace.Disassemble.Inspectthefoamelement.Replaceitifitistornorshowssignsofconsiderablewear.

2.Saturatethenewelementwithengineoil.Then,squeezeittospreadtheoilthroughout.Wrapfoamincleanclothandsqueezetoremoveexcessoil.Inspecttherubberysealinggasketbetweentheaircleanerandcarburetor.Replaceitifitisworn.Reassembleandreinstalltheaircleaner.

PAPERFILTERSANDTIPPINGTHEENGINE

Ifyour4-strokeenginehasapaperfiltercartridge,removeittemporarilyanytimeyouarepreparingtotiptheengineonitsside.You’lleliminateanychancethatoilfromtheprecleanerwillspillontothepaperandruinit.Topreventdebrisfromenteringthecarburetor,temporarilycoverthecarburetoropeningwithplastic.

HowtoServiceaPleatedPaperorDual-ElementAirCleanerDual-elementaircleanerscomeinavarietyofdesigns.Twoofthemostcommonareshownhere.

1.Withthecoverremoved,separatetheprecleaner(ifequipped)fromthecartridge.Tapthecartridgegentlyonaflatsurfacetoremoveanyloosedirt.Inspecttheelementandreplaceitifitisheavilysoiled,wet,orcrushed.

2.Inspecttheprecleaner,ifequipped.Notethemeshbacking,designedtoactasabarrierbetweentheoilyprecleanerandthepleated-paperelement.Ifthemeshbackingisplastic,youcanwashtheprecleaner,wringitout,andletitdry.Don’twashaprecleanercontainingametalbacking;replaceitwhensoiledorworn.Lookforoilinginstructionsontheprecleaner.Ifdirected,lubricatetheprecleanerwithoil.NOTE:Notallfoamprecleanersshouldbeoiled.

3.Cleanthecartridgehousingwithadrycloth.Donotcleanwithsolventsorcompressedair.Reassembletheaircleaner.Iftheprecleaneristheoiledtype,takecaretoinsertthemeshtowardthepaperelementsothatthepaperisneverexposedtotheoil.Reinstall,makingsurethatanytabsonthecartridgeareintheirslotsontheenginehousing.Gapsaroundthecartridgepermitunfilteredairanddamagingdirtparticlestoentertheengine.

Cleaningoffdebrisandgunkisasimplebutcriticalpartofanysmall-enginemaintenanceprogram.

MoreSmartMaintenanceThissectioncoversfouradditionalgreatwaystohelpensureanice-runningengine.Testingenginecompression,inspectingacrankcasebreather,lubricatingcablesandlinkagesandtighteningbolts.Takethesestepswhenyou’reperformingyourpreseasonmaintenance,oranytimeyourengineandequipmenthavebeenoperatingunderaheavyloadordirtyordustyconditionsforawhile.

Somemorespecialtytoolsthatcancomeinhandywhendoingsmall-enginemaintenanceinclude:Extensionwrenchhead(A);six-sidedboxwrench(B);largeoffsetboxwrench(C);ratchetwrench(D):adjustableboxwrench(E).

TESTINGENGINECOMPRESSION

Ifyourenginehasleaksaroundthevalves(4-strokeonly)orrings,compressionoftheair-fuelmixturesuffers.Whenthishappens,performanceandefficiencycandropdramatically.

AspinoftheflywheelwillgiveyouagoodideaofwhetherornotthecompressioninyourengineisOK.

HowtoTestEngineCompression

Disconnectthesparkplugleadandsecureitawayfromthesparkplug.Removetheblowerhousing.Then,disconnectthebrakepadorband,ifequipped(see“ServicingtheBrake,”pages132to137).Spintheflywheelcounterclockwisebyhand.Ifcompressionisadequate,theflywheelshouldreboundsharply.Aweakornonexistent“bounce,”indicatespoorcompression(see“Troubleshooting,”page39,foralistofpossiblecausesandremedies).

OPTION:Foranumericcompressionreading,removeyoursmallengine’ssparkplug,groundtheplugleadtotheengineblock,andscrewthehosefittingofasimplecompressiontester(availableatmostautopartsstores)intothesparkplughole.Pullvigorouslyonthestartercord(orengagetheelectricstarter).Manyexpertssayareadingof100-psirepresentsthebottomofthelowrangeforgoodstarting/running,thoughsomeenginesdefythisdecreebyworkingOKwith80-psi.Yourengine’sservicemanualorlocalshopproprietorshouldhelpclarifya“healthy”number.Inanyevent,knowinganengine’scylindercompressionisasvaluableinsmallenginediagnosticscenariosasisadoctorknowinghis/herpatient’sbloodpressure.

Tools&Materials

•Socketwrenchset•Needlenosepliers•Feelergauge•Spraysolvent/lubricant

Timerequired:15–45minutes

INSPECTINGACRANKCASEBREATHER

Manyenginescontainacrankcasebreathertoventgasesthataccumulateinthecrankcase.Thebreather(ifequipped)isusuallylocatedoverthevalvechamber.

HowtoInspectaCrankcaseBreather

1.Removethemufflerorotherpartstoreachthebreather.Then,loosenthebreatherretainingscrewsandremovethebreather.Makesurethetinyholesinthebodyareopen.Useafeelergaugetocheckthegapbetweenthefibervalveandthebreatherbody.Ifa0.045in.feelergaugecanbeinserted,replacethebreather.Avoidusingforceorpressingonthefiberdisc,andneverdisassemblethebreather.Ifthebreatherisdamaged,replaceit.Replacetheoldgasketthatfitsbetweenthebreatherandtheenginebodywheneveryouremovethebreather.

LUBRICATINGCABLESANDLINKAGES

Controlcablesandlinkagesonthegovernor,flywheelbrakeandthrottlecanseizeandmayeventhrowoffengineperformanceiftheycan’tbemovedfreely.Youcanreducebindingtoaminimumandkeepcablesandlinkagesfreeofdirtanddebrisbysprayingthemoccasionallywithasolvent/lubricant,(photo,right).

TIGHTENINGBOLTS

Boltsonyourenginemustbetightatalltimes.Iftheboltsremainloose,partscaneasilybedamagedduringengineoperation.Becausemechanicaldesignersunderstandanengine’sstressandvibrationcancauseeven“factory-tight”boltstowiggleloose,theysometimesinclude“keeper”washersintheircreations.Typicallyontheboltssecuringcomponentslikeaconnectingrodtoitsrodcap,thesewashersarebentinonespotagainstitsbolt(ornut)flat,asawaytopreventmovement.Sometimes,thefactorysimplyknocksatiny“keeper”dimpleintothealuminumwherethebolthead(ifintheformofascrew/hexhead)isrecessed.Tryingtootherwisetightenorremovesuch“kept”boltsislaterunderstandablymaddening.

Mountingboltsthatattachtheenginetotheequipmentcanalsoloosen,leadingtodamage,suchasacrackedengineblock.Checktheseandallotheraccessiblenutsandboltsduringregularmaintenance,andanytimeyousenseexcessvibration.

Somemountingboltsmustbegraspedwithawrenchfromaboveandtheirassociatednutstightenedwithasecondwrenchfrombeneaththeequipmenttokeepbothendsfromspinning.Othersareself-tapping,andovertighteningcandamagethethreads.Consultyourservicemanualorlocalserviceshopforthepropertorqueforeachboltonyourengine,anduseatorquewrenchforfinaltightening.

LAWNMOWERMAINTENANCETIPS

•MowingDeck:There’snotamowerinexistencethatwouldn’tappreciatetheundersideofitsdeckbeingcleanedofgrassclippingsandwhatnotaftereveryuse.Thisisbestaccomplishedafterremovingthesparkpluglead(preventinginadvertentstarting)andtippingthemowerenoughtogainaccesstothebladeareawithoutspillingfueland(on4-stroke-equippedunits)causingoiltorunoutofthecrankcase.Withhandsinsturdygardengloves,andatrustypaintscraperinonehand,simplyscrapeawayasmuchdebrisaspossiblefromthedeckandblade.Astiffwirebrushcanhelp,too.Somefolksswearbythepracticeofusinganoldpaintbrushtoswabacoatingofusedmotoroilontothemowerdeck.Allofthisshouldresultinamachinethatlastsmanyseasonslongerthanitotherwisewould.

Usearotarytoolwithagrindingwheelorametalfiletosharpenblades.Thebladeshouldberemovedfromthemachineandsecuredinashopvise.

•Blades:Removethebladefromthecrankshaftbyblockingthebladefromturningviapieceofwoodandtakingoffthebolt(s)holdingthebladeinplace.Putthebladeinavise,andwhilewearingeyeprotection,sharpenthebladebyusingeitheraflatfileformetaluseorarotarytooloutfitted

withanappropriatesharpeningwheel(whichwillworkmuchfaster).Ifyouuseafile,pushitacrossthecuttingedgeofthebladeusingtheoriginalanglecutbythemanufacturer.Filingworksontheforwardstrokewhilepushingitdownwithrequisiteforce.Don’tpushbackwiththefileovertheblade.Aimforaniceshinysharpsurfacewiththeprescribedangle.Thosewiththerotarytoolorabenchgrindercangetthesamejobdonefaster.

Checkthebalanceinyourbladebyhangingitatthecenterholefromahorizontalnailandobservingifthebladetopislevel.Grindoffmetalalongthebladeedgetolightentheheavyside,ifany.

Whensatisfiedwiththebladesharpness,insertanordinarynailsidewaysinbetweentheslightlyopenedjawsoftheviseandthenclosethosejawssothatthenailisstickingoutsideways,pointingparalleltothefloor.Balancetheblade(throughthecenterhole)onthenail.Ifthere’saheavyend,filethatside’sbladesurfaceabitmoreandaimforgoodbalance.Suchequilibriumisneededforkeepingthemowerfromvibratinglikecrazy.Reattachthesharpenedblade,setthemowerupright,attachthesparkpluglead,andgogetthatlawn!

•DriveUnits:Ifyoufindthataso-called“self-propelled”mowerisincreasinglydependingonyoutopushit,thedrivesystemprobablyneedswork.Whilegearsmaybeemployed,mostofthesemachinesutilizea

simpledrivebelttransmissiontoshiftfromneutraltoforward.Weakmotionorlaggingistypicallytheresultoflooseorwornbelts.Grassclippingsandmoistureareusualsuspects,too.Cleaning/tighteningisthefirstorderofbusinesshere.Admittedly,somegear-drivenmodelssufferfromproblematicplasticgears.Nomatterthedesign,though,cablesandlinkagesservingtoengagethedrivescanbecleanedandbettersecured,thusfacilitatingimprovedforwardmowermotion.

TILLERMAINTENANCETIPS

Tomostobservers,alltillerslookprettymuchthesame.It’sprobablythegangly,nonmobileappearanceofgardenmachinesortheirreputationforbeingdifficulttowheelthatfrequentlycausesthemtoendupinlong-termstoragewithabucketovertheirengineandinbackofsomeweedyshed.Unlesstheyareequippedwithatransmissiondrivesystemthatactivatesthewheels,theydependupontheforwardmotionoftheirchurningorcuttingtinesforpropulsion.Thatsaid,itisawonderthatoldpowertillerscontinuedoingsomuchdirtyworkfortheirowners.Iftheengineisnotanissue,tillertroublesarealmostalwaysbeltandpulleyrelated.Inthesemodels,cleaning,tightening,andpossiblebeltreplacementwillimproveperformance.Moredeluxeexampleshavewormgeardrivesthatrequirelubricationoranoverhaulifthegearsbecomestripped.

POWERAUGERMAINTENANCETIPS

Essentiallyasmallengineonascrew-typepost-holedigger,iceaugersareincrediblysimplewhencomparedto,say,asnowblowerorgardentractor.Still,otherthanenginemaladies,theyarenotimmunetoailments,especiallyinthecentrifugalclutchorothertransmissionmechanismthatconnectsthemotortotheaugerblade.Ahighengineidlecanstarttheaugerturningimmediatelyuponstart-up.Adjustingtheidletoaslowerpurrshouldsolvethis.Ifnot,it’spossiblethattheclutchspringorrelatedpartsmighthavecomelooseorbroken,resultinginajammeddrivesystem.Here,theonlywaytodeterminethisistotakeitapartforinspection.

LAWNTRACTORMAINTENANCETIPS

Thetermsgardentractorandlawntractorareoftenusedinterchangeablybytheaverageindividual,butthetwomachines—thoughappearingprettymuchidenticaltothatbasicobserver—arenotthesamething.Typically,lawntractors(sometimesdubbed“ridingmowers”)areprimarilydesignedforcuttinggrassaroundhomeswithyardsuptoaboutanacre.There,maneuverabilityiskey,economyisimportant,andparkinginamodestspaceisappreciated.

So,a“gardenvariety”(sotospeak)lawntractorwillprobablyhaveanengineratedatlessthan15-horsepower,begiftedwithsharpturningcapabilities,wearsmallerdiameterbutwidertiresthanagardentractor,andsportamowingdeckcutwidth(withtwoorthreeblades)uptosome42inches.

Gardentractorsmaylookleanerandmorefarmtractor-esquethanlawntractorswhilegettingpoweredbymotorsbumpingintotheupperrangeofthe25-horsepowermaximumunofficialdefinitionofasmallengine.Withthismuscleandtallertires,agardentractorcanbeequippedwithabiggermowerdeckorpull-behindgangmowers,andnicelyhandleattachmentssuchasatrailer,gradingblade,plow,orsnowblower.Propertirepressureisespeciallyvitalwhenaddingtheseimplementstoagardentractororforanyoutdoorpowerequipmentwithpneumatictires.

Somemodernlawntractorsandgardentractorstransferpowerfromenginetowheelsviaanautomotive-type“stick-shift”manualgearboxorperhapsahydrostatictransmission.Thelatteremploysavariablepressurepump(typicallyenlivenedbyabeltdriveoffofthetractor’sengine),pressurereliefvalveandpistonsthatsendpowertoahydraulicmotor.

Acontrolleverworksinconcertwiththepistonsandpressurevalvestoeitherincreaseordecreasethehydraulicfluidflowtothehydraulicmotor,

causesthismotortospeeduporslowdown.Thatmeans,aslongastheengineisrunningatasufficientrpmtoeasilyactivatethepump,thetractor’sspeedisessentiallyaprovinceofthehydrostatictransmission.

Whileamanualtransmissionwithrangesofmeshinggearsrequiresareservoirofconventionaloilinthegearboxanddrivedifferential,oneequippedwiththehydrostatictransmissionmusthaveairtightlinesandcomponentsabletowithstandupto375psi.Suchtranniesgetalothotterthanaregulargearbox,soarefittedwithacoolingfan.

Thetwobigmaintenancerequirementsinhydrostaticunitsaresufficientfluid(changedatleastannually)andcleanlinessofthetransmissioncoolingsystem.Pushingortowingahydrostatictransmission-equippedmachineisnotadvised—duetopossiblefluidbackpressureissues—unlessotherwiseallowedbythemanufacturer.

Therearestilllotsoflawntractorsinservicethathavebelt,pulley,andfrictionwheeltransmissionsvoidofgears.Theirprimarymaintenanceincludescleanliness,andmakingsurethatthebelts,pulleys,andrelatedcontrolcables/linkagesareproperlyengaging.Tracingthesourceofslippageorafunnynoise,andthentighteningtheoccasionalloosepulleyand/orreplacingafrayedorbrokenbeltkeepthisoldtechnologyattractivelysimple.

Lawn/gardentractormowerdeckslikethesamemaintenanceoftheirsmallerlawnmowersisters.Therigamaroleofdetachingthesedecksforcleaningaccess,however,canbefrustratingwhentryingtonegotiateaheavycuttingunitanditsrelatedbeltsandpins.It’sbesttomakeitatwo-personproject.

Asinthelawnmowerversion,besuretowearsturdygardengloveswhenworkingaroundblades,andremembertofirst,eitherremovetheignitionkeyorpullthesparkplugwireoffofitsplug.

SNOWBLOWERMAINTENANCETIPS

Routinelycheckallofthebelts,includingthepropulsionandaugerdrivebelts,forpropertension.Thebeltshaveatendencytoloosen.

Checktheaugergear-caseoiltomakesurethelevelsinthereservoirareadequate.

Evenwithabeautifullyperformingengine,snowblowersneedcaretokeepthemhappyinwinter.

•Don’tgetsnowintheoilfillspout,butmakeahabitofcheckingthelubelevelbeforeeachtimethemachineisstarted.

•Checktheaugergear-caseoilafterevery25hoursofuse,greasingthegearsthathelpturnthesnow-throwerchute,andcheckingdrivebelttensionandlinkagesaftereachfivehoursofoperation.

•Keepthepropulsionandaugerdrivebeltsproperlytensioned,aswetloosebeltsslipeasily,thusreducingthesnowblower’seffectiveness.

•Onmetal-to-metalsurfaces,though,lubricationisvitaltokeeppartsmovingwithagility.Yoursnowblower’smanualshoulddescribetheseneedypoints.Itmaygivespecialattentiontothegreasefittingswheretheaugerbladeridesonitsrotatingshaft.

•Ashearpintypicallykeepstheaugerrotatingwiththisdriveshaft,butrust(fromneglectinggreasing)cancausetheaugertobondtotheshaft,preventingtheaugerfromrotatingfreelyifithitsaseriousobstruction.

And,thatcouldresultinallkindsofsafetyandmechanicalproblems.

•Veteransnowblowerownersagreethatthemostvaluabletipregardingoperatingsuchamachinesafelyisapersonalpledgetoneverclearasnowclogfromtheaugerorchuteareabyhand.Instead,usesomethinglikealongpieceof1-inch-squarescraplumbertocoaxawayaclog.Becarefulnottostandinthewayofthechutewhileclearingtheobstruction.

•Allbutthesmallestsnowblowersareofthetwo-stagevariety,withthemainaugerasstageoneandblowerbladenearthechute’sbasewhirlingrapidlytodrawupthesnoweatenbytheaugerandthenblowitoutofthechute.Ifeitheroneofthosecomponentsisn’tturningproperly,theothercan’tdoitsjob.

FINALLY,ACOUPLEOFGREATWAYSTOCLEANUP

Thosewhocometoappreciateoutdoorpowerequipment,or“OPE,”asmotorenthusiastsandsmall-engineprofessionalssay,findthemselvesgoinginoneoftwoOPEownershipdirections;findingandenthusiasticallyrevitalizingmotorizedequipmentthathasbeengivenupby“regularfolk”ashopeless;or,developinganeyeforhigh-end,preownedequipmentandfindinggreatdealsfromwell-heeledprivatesellerssimplywantingthelatestmodel.Onesuchbuffhasfilledhisstorageshedwiththesevalues,thenmusedonasmall-engineblogthathelovestop-of-the-lineOPEand“appreciatesthequalityandperformancethattypicallygoeswithit.”But,healsoadmitsbeingunwillingtoforkoverbigbucksforpremiumproducts,whichiswhytheguybuysalmostallofhisOPEasgentlyusedequipment,thussavingsignificantmoney.Tothatend,heobservesthatmostpeoplewhooriginallypurchasedhigh-end,high-pricedOPEoffashinyshowroomfloorareusuallydedicatedtotakingverygoodcareoftheirequipmentorroutinelypaytohaveitservicedprofessionally.Becausefinancesarenotaparticularissuewithwealthierhomeownerswhodecidetoupgradetosomethingevenneaterandnewer,theyoftenquicklysell—tosomeonewho’dtrulyappreciateit—theirlate-modelmower,snowblower,orotherOPE.Craigslistandfancyfrontyardsaregreatplacestospotthosetoneyopportunities.Ontheoppositeendofthespectrum,small-enginebuffswantingtopracticethekindofrepairsoutlinedinthisbook,willsearchcurbsontrashdayorlookanyplaceelseharboringrustystuff.There,onemayrealizeatreasuretroveofdiscardedOPEhopingtobecomepartofsomebody’senjoyablyusefulpastime!

BasicEngineRepairs

Oursmall-enginerepairstorycontinues(seepages35and43).TherewasanancientlittlegasstationlessthanamilefromMelinda’shome.

Theoldwomanwhosehusbandrepairedlawnmowers,gardentractors,andtheoccasionaloutboardmotorthere,noticedMelindastrugglingtokeepherbicyclegoing.“Gotaflat,Missy?”shecalledout.Melindawobbledherbiketoastop.“Herb!”sheyelledtoherspouse,“Thisnicegirlneedshertirefixed.”“Kiddo,”hebeganwithMelinda,“getmethatbristlebrushandragover

there.Wegottagetthingscleanfirst.Andwe’llneedthe9/16-inchcombinationwrenchandthatPhillipsscrewdriverwiththeyellowhandleontheworkbench.”Thoughatfirstshehadalmostnoideawhathewastalkingabout,hismethodofshowingherhis“sixpointplan,”startedmakingsense.“Numberone—cleananythingthatpreventsagoodlook,”theoldmanstartedcounting.“Two,inspectthesituation.Diagnosingthetroubleisnumberthree.Then,four,prepareyourtools.Stepfiveiswhenyoudotherepairwork.Andfinally,stepsixistestingyourworktoseeifitwasasuccess.”Puttingthissix-stepplanintoaction,theflatwasrepairedveryquickly.Afewdayslater,whenshereturnedtothegasstationwithaplateofthank-

youcookies,MelindagotofferedaSaturdayjobhelpingHerbandhiswifearoundtheshop.Whereverherassignment,shewasschooledinthevalueoffollowingsomeformoftheoldfellow’splan—fromclean-up,triage-relatedtoolselection,toworkingsystematicallyonarepairprojectandthencarefullytestingtheresults.Shealsofoundittobeamethodicalformattranslatabletoschoolworkandusefulintheengineeringcareersheeventuallypursued.“Ifyoucanfollowasimplesystem,youcanfixjustaboutanyproblem.”

—P.H.

Aworkshopdoesn’tneedtobeafancyplaceoutofacableTVgearheadshow.Justacleanareainyourgaragewithamechanismforhangingtoolsandparts,somegoodlightandventilation,andspacetoworkwilldo.

BasicRepairsMakingeffectivesmall-enginerepairsstartswithyourworkspace.Itshouldbeneat,wellventilated,welllitandwellequipped.Asturdyworkbench,vise,magneticpick-uptool,air-compressororbicyclepump,andbroomcancomeinmightyhandyduringyourrepairprojects.Youcanmakeasimplesmall-enginestandoutofscraplumber,allowingthepowerplanttoberemovedfromitsequipmentmount,butalawnmowerorsnowblowerenginethatisstillmountedtoitshostisusuallyaccessibleandaccessisimprovedbypositioningthepowerequipmentonalargepieceofcardboardoratarp.Thatway,anydroppedpartswillhaveabetterchanceofbeingquicklyfound,andthisworkareacanbemoreeasilykeptcleanthanmightabaregaragefloorordriveway.Takingdigitalpicturesbeforeeachdisassemblystepwillprovideyouwithavividrecordofwhatwentwhere.Youmightnothavetoreferbacktotheimages,butifyoueverdo,they’llproveinvaluable.Zip-topsandwichbagsmakegreatparts“keepers,”especiallywhenthey’relabeledwiththeremovedpart/systemnames.Alsousefulisanoldboardwithsomenailshammeredinjustenoughtoprovideconvenienthooksforwashers,nuts,seals,gaskets,etc.Ifthey’replacedonthe“keeper”nailsinorderofremovalfromtheengine,reversingtheprocesswillbeobvious.Finally,neverunderestimatethevalueofkeepingyoursmall-enginerepairareaclean.Beingcarefulnottoinadvertentlydiscardparts(orcluesintheformofbrokenpieces),periodicblowing/sweepingawayofdirt,gettingridofgreasyglobs,andclearingformerlycaked-ongrassygrimelendsitselftoorganizationbestpracticedforsuccessfulwork.That’swhyourfirst“warm-up”repairprojectinvolvesthewisehabitofkeepingone’ssmallenginecleanandcool.

Completelyremovingdebrisfromyoursmall-enginesystemsisanongoingbattlethatrequiresseveralweapons,fromwipingclothstocompressedair.

RemovingDebrisGrassandotherdebrismayhardlyseemlikeacriticalrepairissueforyoursmallengine.Butonceitaccumulatesinbetweenengineparts,itcancauseatemporarylossofpowerorevenpermanentenginedamage.Debrisundertheblowerhousingorinthecoolingfinsonthecylinderheadcanmakeanengineruntoohot.Prolongedoverheatingmaycauseapistontoseizeinitshostcylinder.Debriscanalsocausegovernorlinkagestobindorpreventairfromreachingthegovernorbladeonapneumaticgovernor,resultingindifficultycontrollingenginespeed.Inspecttheblowerhousingandmufflerareafordebriseachtimeyouuseyourengine.Ifthescreenovertheblowerhousingisclogged,it’sagoodindicationthatdebrishasaccumulatedunderneathaswell.Removetheblowerhousingforamorethoroughinspectionandcleaningattheendofeachseasonofuseandmoreoftenifyouoperateyourequipmentintallorwetgrass.

Tofullyremoveallthedebrisbuildup(thephotoaboveshowsafairlyadvancedcase)oftenmeansdoingsomelightdisassemblytogainfullaccesstotheareaswheredebriscollects.

HowtoInspectforDebris

1.Startbydisconnectingthesparkplugleadandsecuringitawayfromthesparkplug.Snapofftheplasticblowerhousing.Ifthehousingismetal,youwillneedtoremoveasetofscrewsorbolts.Onsomemodels,removingthescrewsrequiresastar-shapedscrewdriverorsocket.Acompletesetofcommonsizesisavailableatmosthardwarestores.Cleanthecoolingfins,theinsideoftheblowerhousing,andtheflywheelfins,usingasmallbristlebrush.

2.Scrapedirtawaygently,usingastiffbristlebrushoraputtyknife.Takecarenottodamagethehousingorflywheel.

3.Toloosenstubborngrit,applyalightsolvent,suchaskerosene,tothebrush.Bewareofsprayingthelikesofstartingfluidorcarburetorcleanerontoanypartswherepaint/decalremovalisunwanted.Dirtanddebrisontheflywheelcuttingscreencanlessentheengine’sabilitytocoolitself.Cleanthescreenthoroughlywithabrush.

4.Removealldebrisbyhandorwiththeknife,screwdrivertip,andbrush.Avoidusingcompressedairhere,astonotforcedebrisintolessaccessibleengineparts.Removeanydebrisfromgovernorlinkages,includingthepneumaticgovernorvane,ifsoequipped.Then,makecertainlinkagesaremovingfreely,usingalightsolventtoloosenremainingdirtanddebris.

5.Checkfordebrisaroundthebrakeassembly.Makesurethebrakecableandlinkagemovefreely.

6.Reattachtheblowerhousingandreconnectthesparkplug.

CHECKINGTHESTOPSWITCH

Ifyourlawnmowerstopsunexpectedlywhileyou’remowingaroundtreesorbushes,youmayhaveaccidentallydisconnectedthestopswitchwire,ashortwireextendingfromthebrakeassemblytotheignitionarmature.Adisconnectedstopswitchwiremaygroundtheignition,preventingthesparkplugfromfiring.Underordinaryconditions,thestopswitchisdesignedtostoptheengineanytimeyoureleasethebrakebailontheequipmenthandle.Youshouldbeabletogettheenginerunningagainbypressingontheflexiblemetaltabonthestopswitchandreattachingthewire.Takecarenottobreakthewireasyoutwistitbackintoposition.Also,checktomakesurethatthesparkplugleadisproperlyattachedtotheplug.

HowtoDegreaseanEngine

1.Withyourequipmentinawell-ventilatedareaandtheengineoff,sprayadegreasingagent,suchasthoseavailableatautopartsstores,liberallyongreasyanddirt-encrustedsurfaces.Waitfifteenminutestoallowgreaseanddirttobreakdown.

2.Wipeawaytheresiduewithacleancloth.

3.Hoseofftheequipmentsurfacesandthenallowthemtodrycompletelybeforestoring.

ServicingtheFuelTankFueltanksaredesignedtokeepyourengine’sfuelclean,vented,andsecure.Ifyouspotdebrisinthetankorleakinggasoline,it’stimeforfueltankmaintenance.Ifyoufindacrackorahole,anewtankistheanswer.Oldermodelsaremadeofsteel.Newermodelsaremadeofaluminumorplastic.Ineithercase,don’trepairadamagedtank.Itposesariskofleakage,fire,orfuelcontamination.

Tanksaretypicallyinstalledasfarawayaspossiblefromthehottestareasoftheenginetokeepthefuelcool.Otherfactorscanalsodamageyourtank.Itcancrackduetolong-termexposuretohotsunandotherelements,orifitisusedtosupportweightfromoutside.Tanksoftencrackundersuchstress.Sometimesthetankhoseflangegetscrackedorbroken,too.Ifyou’rereplacingafueltank,useonlypartsrecommendedbytheenginemanufacturer.Thesepartswillattachsecurelytoyourengineinthespaceprovided.Manyfueltanksaredesignedtouseaventedfuelcaptopreventavacuumfromforminginthefuelline.Checktodetermineiftheventholeisobstructed.Iffuelisleakingfromthecap,aproperlyfittedreplacementcapcansolvetheproblem.

NOTE:Yourtankmayalsocontainafuelfilter(see“ServicingtheFuelFilter,”pages75to76).Checkitoccasionallyfordebrisandsignsofwater.

Fueltanksmustbeconstructedofanoncorrosivematerialorcoatedwithacorrosion-resistantlayertoprotectagainstthedamagingeffectsofwater,alcohol,andsalt.Ifthetankisdesignedtodeliverfuelthroughafuelline,aconvexfuelfiltermaybelocatedatthebaseofthetank,wherefuelfromthetankentersthefuelline.Afiltercanalsobelocatedoutsidethetank,midwayalongthefuelline.Manyolderengineswerenotequippedwithafuelfilter,thoughagenericonemaybeaddedifthere’ssufficientroomtocutthefuelline(typicallyatcenterlength)andinsertit.

Tools&Materials

•Baster•Flashlight•Longtweezers•Fuellineclamp•Screwdriver•Socketwrench

Timerequired:30minutes

LABYRINTHFUELTANKS

Ifyourtankmustsustainexcessivevibrations,youcaninstallalabyrinth-equippedtankonsomeenginemodels.Thelabyrinth,availablefromyourauthorizedservicedealer,containsasetofbafflesand/orafoaminserttoreducethesloshingandvaporizationoffuel.

HowtoRemoveandCleantheFuelTank

1.Removethesparkplugleadandsecureitawayfromtheplug.Useafuellineclamporothersmooth-facedclamp(suchasa1-to3-inchC-clamp)tosealthefuellinewhereitattachestothecarburetor.Then,disconnectthelinefromthecarburetor,holdthelineoverabucketorfuelcanandreleasetheclamp.Disposeofallfuelinasafemanner(see“GasolineUse,”page77).

2.Checkwithaflashlightfordebrisandbeadsoflightthatindicateholesorcracks.Useabasterorlongtweezers(tograspsolids)toremoveloosedebrisfromthetank.Oncethetankisfreeofliquids,itcanbeshakenupsidedownwiththecapoffinordertoevacuatestubborndebris.Ifyoufinddamagethatquestionsthetank’sintegrity,replacethetankwithoriginalmanufacturer’sequipment.Inspectthefuelfilterfordebrisordeposits(seenextpage).Reattachthefueltankorinstallanewtank,fasteningitfirmlywiththecapscrews.Thisisagoodopportunitytoreplacethefuellineandfilter,usingoriginalmanufacturer’sequipmentorqualitygenericsrecommendedforyourmachine.

ServicingtheFuelFilterAcleanfuelfilterstrainsthefuelbeforeitreachesthecarburetorandpreventsforeignparticlesfromcloggingyourengine.Adirtyfuelfiltercanmaketheengineruntoolean,withdiminishedperformanceandunevenoperation.Otherfactorscancausetheseproblems,butthefuelsupplyisoneoftheeasiesttocheck.

Somefiltersarelocatedinsidethetank,othersarefittedintothefuellinebetweenthetankandthefuelpump.Mostuseeitherameshscreenorpleatedpaper.Thesizeoftheholesinthefilterwilldeterminethelargestparticlesthatcangetthroughthefilter,andthenumberofholeswillaffecttheamountoffuelthatcanflowthroughthefilter.

Filterscontaineitherameshscreenorapleated-paperelement,andareratedbythesizeoftheholesinthefilteringmaterial,expressedinmicrons(μ).Pleated-paperfilters,designedforuseinthefueltank,aretypicallycontainedinaclearplasticcasingandrated60μ.Theyconsistofmultiplefoldsthatstrainoutparticlessuspendedinthefuel.

Theproperfilterforyourenginedependsontheengine’sdesign.Consultyourowner’smanualorsmall-enginepartsretailerforthecorrectreplacementfilter.

Onrareoccasionsthefueltankmaycontainafuelfilter,butinalmostallcasesitwillbefoundin-lineonthefuellineleadingfromthetank.

Tools&Materials

•Flashlight•Fuellineclamp•NeedlenosepliersTimerequired:20minutes

HowtoInspectaFuelFilter

1.Shutthefuelvalve,iftheengineisequippedwithone.It’slocatedatthebaseofthefueltank,wherethefuellineisattached.Ifyourtankisnotequippedwithafuelvalve,clampthefuelline,usingafuellineclamp(seepage74).Ifyourfilterisinstalledinthefuelline,removethemetalclipsoneachsideofthefilter,usingneedlenosepliers,andslidethefilteroutofthefuelline.

2.Shakethefilteroveracleanclothtodisplaceanyremainingfuel,thenusetheclothtowipeawayanyresiduefromtheoutsideofthefilter.Keepthefilterasafedistancefromyourfaceandlookintooneend.Youshouldbeabletoseelightshiningthroughclearlyfromtheotherside.Ifanythingiscloggingthemeshscreenorpleatedpaperortheinsideofthecasing,replacethefilter.

SAFETYTIP

Wearsafetyeyewearwheneverremovingorinspectingafiltertoprotectyoureyesfromliquidfuelorfuelvapors.Haveadryclothhandytoholdthefilterandcatchanydrippingfuel.Ifthefilterisinstalledinsidethetank,youwillneedtodrainthetankbeforeyoucanremovethefilterforinspectionorreplacement.

Heavier-dutysmallenginescontainafuelfilter.Asamplingofin-linefiltersareseenabove.Ifyoudon’tfindafiltermountedinyourfuelline,lookforoneinsidethefueltank(seepage75).

WHICHGASOLINETOUSE?

Useonlyfreshunleadedgasolineinyoursmallengine.Hereareafewothertipsforgasolineusein4-strokesmallengines.•Usegasolinewitha77octaneratingorhigherforL-headenginesand85orhigherforoverheadvalveengines.Sincesmallenginesoperateatrelativelylowcompressionratios,knockingisseldomaproblem,andusinggasolinewithahigheroctaneratingisunlikelytoofferanybenefit.

•Usinggasthatisoveramontholdanddoesnotcontainagasolinestabilizermayresultinhardstartingandvarnishformation.Drainthetankiffuelsitsformorethanamonth.TheEnvironmentalProtectionAgencyrecommendspouringoldfuelintoyourcar’sgastank.Aslongasthecar’stankisatleasthalffull,theoldfuelwillmixharmlesslywiththenewandwillnotaffectyourcarengine.

•Four-strokeenginesareusedonmostlawnmowersandlargelawnequipment.NEVERuseanoil-gasolinemixtureina4-stroke,sincetheenginehasanindependentoilsupply.Ifyoufindanoilfillcapleadingtothecrankcase,youcanbesureyourengineisa4-stroke.

BEWAREOFETHANOL

Ethanolblendedgasolinesarenofriendstosmallengines,especiallytheolderones!Itsalcoholcontenttendstoeatrubbergaskets,drawmoistureoutoftheambientair(thinkdampgarageandamowerorsnowblowerthatsitsaroundbreathingmoistairforweeks!),andpromotescorrosion.

EvennewenginesbuiltaroundtheEthanolrealitycanbesubjecttothenegativeimpactsofthis10percentadditiveinmotorfuel.And,increasedEthanolpercentages,suchasinE-85orotherso-called“flex-fuels”canreallycauseasmallenginebigproblems,soshouldneverbefedtoyourlittlemotorbuiltasofthisbook’spublicationdate.

ThoughnotneedingthehigheroctaneofanunleadedandEthanol-freepremiumfuelavailablefromgasstationsofferinganalternativetoEthanol,someluckysmallenginesarefedthisfuelbytheirownerswhoavoidbeing“pennywiseandpoundfoolish.”Otherstreattheirsmallengine’sfuelwith“Ethanoladditivecures”availableatautopartsstores.

Admittedly,gasolinethatcontainsEthanolisamajorsubjectofcontroversyinsmall-engine/outboardmotorcircles.Nodoubt,anyonewhomentionsthetopicwillgetamplecommentary.Ifyoursmall-engineisnewenoughthatyouknowwhereitcamefrom,consultingthedealerisagoodavenueofspecificallyhelpfuladvice.

ServicingtheFuelPumpAfuelpumpisusedwhenthefueltankismountedlowerthanthecarburetorandcannotrelyongravitytocarryfuelthroughthefuelline.Fuelpumpshaveeitheraplasticorametalbodyanddeveloppressureusingthevacuuminthecrankcase,whichiscreatedbythemotionofthepiston.Afittingonthecrankcasecoverorthedipsticktubedrawsonthecrankcasevacuumtocreatethepressuretopumpfuel.

Thefuelpumpmaybemountedonthecarburetor,nearthefueltankorbetweenthetankandcarburetor.

Thepartsofatypicalsmall-enginefuelpump.Thedevicereliesuponvacuumpressuregeneratedbythepistonmotiontoadvancethefueluplinefromthetank.

Tools&Materials

•Carburetorsolventorlacquerthinner•Needlenosepliers•Socketwrenchset•Screwdrivers(standardandPhillips)•Solvent

Timerequired:45minutes

HowtoInspectaFuelPump

1.Turnoffthefuelvalve(ifequipped)atthebaseofthefueltank,wherethefuellineisattached.Ifthereisnofuelvalve,stoptheflowoffuel,usingafuellineclamp.Loosenthemountingscrewsandremovethepumpfromthemountingbracketorcarburetor.

2.Checkforhairlinecracksandotherdamagetotheexternalsurfacesofthepump.Ifthepumpisdamagedandhasametalbody,discardthepumpandinstallareplacementpumpfromtheenginemanufacturer.

PLASTICBODYOPTION1:Ifthepumphasaplasticbody,obtainamanufacturer’srepairkitsoyoucanreplacewornparts.Checkthehosesforcracks,softeningorhardening,andreplaceanyfaultyparts.Discardoldgaskets,diaphragms,andsprings,andreplacethemwithnewpartsfromthekit.

PLASTICBODYOPTION2:Withthefuelvalveclosedorthelineclamped,removethemountingscrews.Then,disconnectthefuelhoses,usingneedlenoseplierstoloosentheclips.Removethescrewsanddisassemblethepump.Inspectthebodyforcracksorotherdamage.Soakmetalpartsinall-purposepartscleaner.Thepumpbodymaybesoakedforuptofifteenminutes.

REINSTALLINGTHEPUMP

Hereishowyoureinstallafuelpump:Referringtothephotoonpage78,placethediaphragmspringandthenthecupoverthecenterofthepumpchamber.Alsoinsertavalvespring.Installthediaphragm,gasketandcoverandattachwithpumpscrews.Tightenthescrewsto10to15inch-pounds,usingatorquewrench.Attachthepumptothecarburetorormountingbracket,usingthepumpmountingscrews.

ServicingtheCarburetorAbigpartofensuringasmooth-runningengineiskeepingyourcarburetorandlinkagescleanandwelladjusted.Thelinkagesattachedtothecarburetor’sthrottleandchokeplatescanbindorstickwhendirty.Constantvibrationandwearcanaffectthesettingsofthecarburetor’smixturescrews.

Withallofthegrass,twigs,andotherdebristhatasmallengineencounters,it’snotsurprisingthatevenpassagesinsidethecarburetoreventuallypayaprice.Depositsinsidethecarburetorcanclogfuelandairpassagesandreduceperformanceorstoptheenginealtogether.Luckily,youcantakecareofmanyoftheseproblemsquicklyandeasily—oftenwithoutevenremovingthecarburetorfromtheengine.

Thesmallcarburetorsfoundonmostsmallenginesperformessentiallythesamefunctionasanautomotivecarburetor(priortofuelinjection).Theycontainthechokeplatethatallowsfuelandairintothecombustionchamber.Alsoliketheirautomotivecounterparts,theyoccasionallyneedtobecleaned,adjusted,rebuilt,orreplaced.

Tools&Materials

•Carburetorcleaner(spray-type)•Safetyeyewear•Screwdrivers(Phillipsandstandard)•Socketwrenchset•Tachometer

Timerequired:1hour

HowToFindtheSourceofaFuelSupplyProblem

Removetheaircleanerandinspectthechokeplatemountedonashaftattheopeningofthecarburetor’sthroat.Checkthatthechokeplatecloseseasilyandcompletely.Achokethatdoesnotmovefreelyorcloseproperlycancausedifficultiesinstarting.Sprayasmallamountofcarburetorcleanerontheshaftofasluggishchokeandintotheventuritoloosengrit.Dabthepartsdrywithacleanrag.Debrisinthecarburetoroftencausesperformanceproblems.

Removeandinspectthesparkplug.Awetplugmayindicateover-choking,waterinthefuel(see“ServicingtheFuelTank,”pages78to79),oranexcessivelyrichfuelmixture.Adryplugmayindicateapluggedfuelfilter(see“ServicingtheFuelFilter,”pages75to76),leakingmountinggasketsoneitherendofthecarburetor,orastuckorcloggedcarburetorinletneedle.

Openthefuelvalve(ifequipped),locatedatthebaseofthefueltankwherethefuellineisattached.Removethelineandcheckforblockage.Fuelwillnotreachthecarburetorifthefuelvalveisclosed.Also,iftheengineisequippedwithafuelpump,makesureitoperatesproperly(see“ServicingtheFuelPump,”pages78to79).

Injectasmallamountofcombustiblefluidintothesparkplughole:toavoidspillage,trysprayingalittlebitofstartingfluidintotheholethroughthenozzleextensionorwithanautomotivefunnel.Youcanalsouseadabofgasoline,butyoushouldavoidhandlingfuelasmuchaspossible.Oncethecombustiblefluidisinthehole,screwthesparkplugbackinandstarttheengine.Ifitfiresonlyafewtimesandthenquits,assumeadryplugconditionandconsiderthecausesofadryplug,listedinthepreviousstep.

HowtoAdjusttheIdleSpeed&Mixture

1.Onsomefloat-typecarburetors,youcanadjusttheair-fuelmixtureandenginespeedatidle.Checkforanidlespeedscrewdesignedtokeepthethrottleplatefromclosingcompletely(see“PartsoftheCarburetor,”page101)andanidlemixturescrewthatlimitstheflowoffuelatidle.Ifyourcarburetorcontainsthesescrews,removetheairfilterandaircartridge.Locatetheidlemixturescrewandturnitclockwiseuntiltheneedlelightlytouchestheseat.Then,turnthescrewcounterclockwise11/2turns.Ifyourcarburetorhasamainjetadjustmentscrewatthebaseofthefloatbowl,turnthescrewclockwiseuntilyoufeelitjusttouchtheseatinsidetheemulsiontube.Then,turnthescrewcounterclockwise1to11/2turns.Replacetheaircleanerassemblyandstarttheengineforfinalcarburetoradjustments.Runtheengineforfiveminutesathalfthrottletobringittoitsoperatingtemperature.Then,turntheidlemixturescrewslowlyclockwiseuntiltheenginebeginstoslow.Turnthescrewintheoppositedirectionuntiltheengineagainbeginstoslow.Finally,turnthescrewbacktothemidpoint.

2.Usingatachometertogaugeenginespeed,settheidlespeedscrewtobringtheengineto1750rpmforaluminum-cylinderenginesor1200rpmforengineswithacast-ironcylindersleeve.

3.Withtheenginerunningatidle(insetphoto),holdthethrottleleveragainsttheidlespeedscrewtobringtheenginespeedto“trueidle.”Then,repeattheidlemixturescrewadjustmentsfromStep1tofine-tunethemixture.

ADJUSTINGTHEHIGH-SPEEDMIXTURE

Someoldercarburetorscontainahigh-speedmixturescrew,nearthethrottleplateandoppositetheidlespeedscrew.Underload,thehigh-speedcircuitincreasesairflowthroughthethroat.Settingthehigh-speedmixtureinvolvesrunningtheengineuntilitiswarm,stoppingittoadjustthehigh-speedmixtureandthenrestartingforfinaladjustments.Runtheengineforfiveminutesathalfthrottletobringittoitsoperatingtemperature.Then,stoptheengine.Locatethehigh-speedmixturescrewandturnitclockwiseuntiltheneedlejusttouchestheseat.Then,turnthescrewcounterclockwise11/4to11/2turns.RestarttheengineandsetthethrottlepositiontoHIGHorFAST.Turnthehigh-speedormainjetscrewclockwiseuntiltheenginebeginstoslow.Then,turnthescrewtheotherwayuntiltheenginebeginstoslow.Turnthescrewbacktothemidpoint.

Onceadjusted,checkengineaccelerationbymovingthethrottlefromidletofast.Theengineshouldacceleratesmoothly.Ifnecessary,readjustthemixturescrews.

ADJUSTINGTHECHOKELINKAGE

Removetheaircleanerandlocatethechokeleverontheengineorontheremoteenginespeedcontrols.MovetheequipmentcontrolstoFASTorHIGH(left).Loosenthecablemountingbrackettoallowmovementofthecablecasing.Movethecablecasingsothechokeisclosed.Tightenthecablemountingscrew(rightphoto)andcheckthemotionofthecontrollever.Repeatthesteps,asnecessary,untilthecablemovesfreely.

AdjustingtheGovernorAproperlyadjustedgovernorcanmaintainasteadyenginespeedregardlessofchangesintheterrainandotherconditionsthatincreasetheworkoftheengine.Theseconditionsareknownasthe“load.”Whenenginespeedstartstoriseorfallinresponsetoachangeintheload,thegovernorresponds,openingorclosingthethrottle.Ifyouadjustenginespeedmanually,usingtheequipmentcontrols,thegovernor’sjobistomaintainthenewsetting.

Yourenginecontainseitherapneumaticgovernororamechanicalgovernor(see“GovernorSystem,”page25).Removetheblowerhousingtodeterminewhichoneyourengineuses.Pneumaticgovernorlinkagesconnecttoapivotingairvanenexttotheflywheel.Onamechanicalgovernor,thelinkagesconnecttoagovernorshaft(seephoto,above).

Foreithertype,followthestepsinthesepagestoadjustyourgovernorforbestperformance.NOTE:Governoradjustmentproceduresvarywidelydependingonthemakeandmodeloftheengine.Checkwithyourauthorizedservicedealerforthespeedsettingsforyourequipment.

Mechanicalgovernor:Amechanicalgovernorusesgearsandflyweightsinsidethecrankcaseasaspeed-sensingdevicethatdetectschangesintheloadandadjuststhethrottleaccordingly.

Thetangbendingtoolisthemostcommontoolforsettinggovernorspringtension.It’sasimplemetalleverwithforkedendsforbendingthetabs,ortangs,onthegovernorandotherengineparts.

Tools&Materials

•Standardscrewdriver•Combinationwrenchset•Socketwrenchset•Tangbendingtool

Timerequired:45minutes

PARTSOFTHEMECHANICALGOVERNOR

1.Enginespeedcontrol.Movingthislevertoahigherspeedsettingopensthethrottleindirectlybypullingonthegovernorgearbracket.

2.Governorgearbracket.Thebracketpivots,increasingtensiononthegovernorspring.

3.Governorspring.Tensiononthespringpullsonthegovernorleverinanefforttoopenthe

throttleplate.

4.Governorlever.Theleverpivots,pullingonthethrottlelinkageandapplyingpressuretothegovernorshaft.

5.Governorshaft.Theshaftlinksthegovernorlinkagesandleverstothegovernorcupandotherpartsinsidethecrankcase.

6.Throttlelinkage.Thelinkagetugsonthethrottlelever.

7.Throttlelever.Theleveropensthethrottleplate,allowingmoreair-fuelmixtureintothecombustionchamber,causingenginespeedtoincrease.

8.Governorgear.Increasedenginespeedcausesgovernorgeartospinfasterandflyweightstoflyoutward.

9.Flyweights.Movementoftheflyweightsappliespressuretothegovernorcup.

10.Governorcup.Governorcupcausesthegovernorlevertopivot.

INSPECTINGTHEGOVERNOR

1.Withthesparkplugleaddisconnectedandsecuredawayfromthesparkplug,checkthatthegovernorlinkagesareattachedandmovefreelybypullinggentlyonthethrottlelever.Thisshouldstretchthegovernorspringwhilepressingonthegovernorlever.Ifnot,checkthatthegovernorspringandthelinktothegovernorleverareproperlyattachedtothethrottlelever.

2.Springsandlinkagesthatarenotattachedmaybereconnectediftheyareingoodcondition.Twistthemcarefullyintoplacetoensurethatthedelicatespringsandlinkagesaren’tpermanentlybentorstretched.Donotusepliersorothertoolstobendordistortlinksorsprings.Replacethegovernorspringifitisoverstretchedandreplacethelinkagesiftheyappearworn.

HUNTINGANDSURGING

Yourenginemayraceorslowintermittentlyevenwhentheloadandthespeedcontrolsettingsareunchanged.Followthestepsbelowtodeterminewhetherthesourceofthiserraticenginebehavior—knownas“huntingandsurging”isthecarburetororthegovernor.

1.Checkthatspringsandlinkagesmovefreelyandthatthegovernorspringisinsertedproperlyonthegovernorleverarm(above).Onamechanicalgovernor,performastaticgovernoradjustment(opposite).

2.Runyourengineateachofitsspeedsettingstodeterminewhenhuntingandsurgingoccur.Iftheproblemcropsupat“trueidle”(whenthethrottleleverisagainsttheidlespeedscreworstop),theair-fuelmixtureisthelikelycause.Anairleakordebrisinthecarburetorisprobablycausingtheair-fuelmixturetofluctuate.Removeandcleanyourcarburetor(seepages100to107).

3.Ifhuntingandsurgingoccurattopno-loadspeed,runthefollowingtest.Movethethrottleleversothethrottleplateisintheopenposition.Ifhuntingandsurgingcontinue,theproblemisprobablyinthecarburetor.Cleanandadjustthecarburetor(see“OverhaulingtheCarburetor,”page100).Ifhuntingandsurgingiseliminatedbyopeningthethrottle,lubricatethegovernorlinkagetoeliminateanyresistanceandbinding.Ifhuntingandsurgingpersist,replacethegovernorspring(s)andretest.

4.Someengineshaveaseparate“governedidle”springandgovernedidleadjustingscrewtopreventstallsunderlightloads.

Ifhuntingandsurgingoccursunderlightload,runthefollowingtest.Lookforanidlespeedscrew,astopscrewontopofthecarburetor,designedtopreventthethrottlefromclosingcompletely.Holdthethrottleleveragainsttheidlespeedscrewandincreasethegovernedidlespeedbyturningthescrewslowlyclockwise.Ifhuntingandsurgingstop,replacetheidlespringandlinkageandresetthegovernedidlespeed.Ifhuntingandsurgingcontinue,cleanandadjustthecarburetor(see“OverhaulingtheCarburetor,”pages100to107).

ADJUSTINGTHE“STATIC”SETTINGONAMECHANICALGOVERNOR

Thefollowingprocedureeliminatesplayinamechanicalgovernorbetweenthegovernorcrank—thearmthatprotrudesfromthecrankcase—andgovernorsystemcomponentsinsidethecrankcase.Thisproceduredoesnotapplyifyourenginehasapneumaticgovernor.

1.Loosentheclampboltonthegovernorcrankuntilthegovernorlevermovesfreely.

2.Movethethrottleplatelinkageuntilthethrottleplateiswideopen.(Tofindthewide-openposition,firstpositionthethrottleleveragainsttheidlespeedscreworafixedstopplate.Thethrottleiswideopenwhenitisallthewayintheoppositedirection.)Notethegovernorarm’sdirectionofrotationasyoumovethethrottleplatetothewide-openposition.Thisisimportantforthenextstep.

3.Withthethrottleplatewideopen,useanutdriverorwrenchtoturnthegovernorshaftinthesamedirectionthatthegovernorarmtraveled.

4.Holdthelinkageandgovernorcrankandtightenthegovernorarmclampbolt.Movethelinkagemanuallytomakesurethereisnobinding.

ADJUSTINGGOVERNEDIDLE

Someenginescontainashorter,smaller,“secondary”governorspringtodiscouragestallswhentheengineisoperatingatidleunderalightload.Undertheseconditions,thesecondaryspringkeepstheengineata“governedidle”speedslightlyaboveitstrueidlespeed.Theidlespeedscrewisalwayssetatlessthantheengine’sgovernedidlespeed.Theprocedureforadjustinggovernedidlevariesdependingontheenginemodel.Consultyourowner’smanualfortheprocedureforyourmodel.

Keepinmindthatthesecondaryspringaffectsallgovernorsettings.Ifthegovernoronyourenginehasasecondaryspring,youneedtoadjustthegovernedidlebeforesettingtheengine’stopno-loadspeed.

TANGBENDINGANDOTHERADJUSTMENTMETHODS

Thetangbendingtoolpicturedonpage84(bottom)isthemostcommontoolforgovernorspringadjustment.It’sasimplemetalleverwithforkedendsusedforgraspingandbendingthetabs,ortangs,onthegovernorlever,springanchor,andotherengineparts.Bendingatangincreasesordecreasestheextensionofthegovernorsprings.

Ifthegovernorleverhasmultiplespringholes(photoA),youcanincreasetopno-loadspeedbyselectingaholethatisfartherfromthepivotpointonthegovernorlever.Onsomeengines,anadjustmentscrewaltersgovernorspringtension,increasingordecreasingtopno-loadspeed(photoB).Fineadjustmentsmaystillrequiretheuseofatangbendingtool(photosD,E,andF).

SETTINGTOPNO-LOADSPEED

IfyourengineraceswhenyousetyourcontrolstoHIGH,youneedtoreducetheengine’stopspeedunderno-loadconditions.Askyourauthorizedservicedealerforthepropertopno-loadspeedsettingforyourmodel.(Ifyourgovernorcontainstwosprings,skipto“SettingDual-SpringTopNo-LoadSpeed,”below).Themostcommonmethodforadjustingtopno-loadspeedistouseatang

bendingtool(see“TangBendingandOtherAdjustmentMethods,”oppositepage)tobendthespringanchortangtostretchorrelaxthespring.

1.AttachtheTinyTachtotheengine’swhitegroundwirewiththealligatorclip.Theredwireshouldbewrappedaroundthesparkpluglead(photoC).Runtheengineforfiveminutessoitreachesitsoperatingtemperature.

2.Placetheequipmentonahard,smoothsurfacewiththeenginerunningandthecontrolssettoHIGH.Decreasetopno-loadspeedbybendingthetangtowardthegovernorspring,untilthemanufacturer’sspecifiedspeedsettingisattained(photoD).Increasetopno-loadspeedbylengtheningthespring.

3.Ifyourenginehasamechanicalgovernor,proceedwiththestaticgovernoradjustment(see“Adjustingthe‘Static’SettingonaMechanicalGovernor,”page87).

SETTINGDUAL-SPRINGTOPNO-LOADSPEED

Ifyourgovernorcontainstwosprings,thesmaller,shorterspringisthesecondaryspringandmustbeadjustedtopreventstalls.

1.Attachatachometertotheengine.Withtheenginerunning,bendthesecondaryspringtang(see“TangBendingandOtherAdjustmentMethods,”oppositepage)sothereisnotensiononthesecondaryspring(photoE).

2.Bendtheprimarygovernorspringtanguntiltheenginespeedis200rpmbelowthemanufacturer’sspecifiedtopno-loadspeed(photoF).

3.Bendthesecondarygovernorspringtanguntiltheenginereachesitstopno-loadspeed.Askyourauthorizedservicedealerforthetopno-loadspeedsettingforyourengine.

4.Ifyourenginehasamechanicalgovernor,proceedwiththestaticgovernoradjustment(see“Adjustingthe‘Static’SettingonaMechanicalGovernor,”page87).

ReplacingtheRewindTherewindstartingsystem,alsoknownasarecoilsystem,isoperatedmanuallybypullingarope.Theropeisattachedtoapulleyandreturnspringthatspintheflywheeltostartthesparkplugfiringandtheenginerunning.Astrongtugisusuallyrequired,sincetheflywheelmustspinfastenoughtogeneratethehighvoltagenecessaryforignition.

Ifyourrewindbindswhenyoupullitordoesnotrewindfreely,itmaybetimetoreplaceit.Thissectioncoverstheproceduresfortestingandreplacingyourrewindassembly.

Therewindassemblyconsistsofapullrope,aflywheel,andarewindspringthatcausesthepullropetorecoil.

Tools&Materials

•Needlenosepliers•Powerdrill•Socketwrenchset

Timerequired:45minutes

TESTINGTHEREWIND

Ifyoudiscoveranyofthefollowingconditions,replacetheentirerewindassembly.

1.Pulltheropeslowly(photoA).Ifthesystemisnoisy,binds,orfeelsrough,thereturnspring,pulley,orropemaybejammed.Ifthecrankshaftdoesn’tturn,theratchetingmechanismisn’tengaging.

2.Oncetheropeisallthewayout,checkforfrayingandwearalongitsentirelength.

3.Lettheroperewindslowly.Ifitfailstorewind,thepulleymaybebindingorthereturnspringmaybebroken,disengaged,orworn.

REPLACINGTHEREWIND

Onsomeengines,therewindisspot-weldedorrivetedtothetopoftheengineshroud.Onothers,itisattachedwithnutsorbolts.1.Loosentheappropriateboltsandremovetheblowerhousing(see“RemovingDebris,”pages69to71).

2.Removethenutsorboltsontherewind(ifequipped)ordrillouttherivetsorspotweldswitha3/16-inchbit,drillingonlyfarenoughtoloosenthem(photoB).

3.Installareplacementrewindfromtheoriginalenginemanufacturer.Insertthemountingboltsfrominsidetheblowerhousingsothatthebottomscomethroughthetopoftheshroud.Placethereplacementrewindovertheboltsandfastenawasherandnutsecurelyoneachbolt(photoC).

REWINDSAFETY

Arewindassemblycontainsapulleyandspringthatretracttheropeaftereachpull.Disassemblingarewindisbestlefttoasmall-enginetechnician.Theprojectrequiresspecialcareandsafetyprecautionsbecauseoftheriskofseriousinjuryfromaspringorotherflyingparts.

Inspecting&ChangingtheMufflerOneofthemainsourcesofsmall-enginenoiseisthehotgasesthatareforcedoutofthecylinderduringeachexhauststroke.Amufflerdoesagoodjobofreducingexhaustnoise.Butafteraseasonortwo,exhaustgasesleavealayerofsootinthemufflerthatcreatesadditionalresistancetogasesexitingthecylinder.Whenhardsootaccumulates,whentheexhaustemitsexcessivenoise,orwhencracksorholesappear,don’ttrytorepairthemuffler.Onceamufflershowssignsofdeterioration,replaceit.Thissectioncoverstheproceduresforremoving,inspectingandreplacingyourmuffler.It’saninexpensiveandsimplejobifyoutaketheproperprecautions.Alwayswaitfortheenginetocoolcompletelybeforehandlingthemuffler.Themuffler’ssurfacecanremainveryhotandcaneasilycauseaburn,evenlongaftertheengineisstopped.Arustymufflercancutyou,especiallyifitcrumblesduringreplacement.Ifanysharpedgesareexposed,useslip-jointplierstoremovethemuffler.

Whenyoursmallengine’smufflerisreadyforreplacementyouwillknowjustfromtheenginenoise.Theseimportantpartsarenotrepairable:bettertofindthecorrectreplacementmufflerandswapitin.

Tools&Materials

•Hammer•Mallet•Metalsnips•Pipewrench•Pinpunch•Slip-jointpliers•Socketwrench

Timerequired:30minutes

TIP

HOT!Keepyourdistancefromthemufflerandotherenginepartsuntiltheenginehashadplentyoftimetocool.

HOWYOURMUFFLERWORKS

Theforceofexhaustgasesastheyrushthroughthesmallopeningintheexhaustvalveproducesshockwaves.It’sthemuffler’sjobtoreducenoisebyroutingtheexhaustthroughaseriesofperforatedbafflesandplatesthatbreakupthesoundwaves.Theinsideofthemuffleralsofunctionsasasparkarrestor,preventingexhaustsparksfromexitingandignitingdrygrass,leaves,ordebris.

Wequicklynoticewhenamufflerisnotdoingitsjob.Evensmallcracksorholesinthemufflercanresultinadramaticincreaseinenginenoise.

Whenit’stimetoreplacethemuffler,useoriginalmanufacturer’sequipmentoraqualitygenericsuitableforyourmodel,thuspromotingsafetyandoptimalengineperformance.Asyoucanseefromthisphoto,mufflerscomeinaverywidearrayofsizesandshapes.

INSPECTINGTHEMUFFLER

1.Locatethemuffler,whichisusuallynearthecylinderhead.

2.Checktheoutsideofthemufflerforsignsofrust,dents,holes,orcracks,anyofwhichcanrestricttheexhaustandreducetheeffectivenessofthemuffler.

3.Ifthere’ssootneartheexithole,removethemufflertocheckforsootinside.

REMOVINGTHEMUFFLER

Themufflerbodymaybeattacheddirectlytotheenginewithmountingboltsorscrewedintotheenginebody.Onsomemufflers,anextendedpipethreadsintotheengine.

1.Ifthemufflerisattachedwithmountingboltsandhaslockingtabsaroundthebolts,bendthetabsbackfarenoughtofitawrenchovertheboltheads.Removethebolts(photoA)anddetachthemuffler.

Ifthemufflerscrewsdirectlyintotheengine,applysomepenetratingoil/lubricanttothethreads(photoB)andlettheoilworkforseveralminutes.Tiptheengineveryslightly,ifnecessary,toallowtheoiltoreachthethreads.NOTE:Don’ttiptheenginesharply.Ona4-stroke,thiscancauseoiltodrainintothecarburetorandaircleaner.

Somemufflersarefastenedwithathreadedlockring.Loosenitbytappingitcounterclockwisewithahammerandpinpunch.Then,graspthemufflerwithslip-jointpliersandunscrewcounterclockwise(photoC).

2.Tocheckforsoot,tapthemufflerbodywithamalletoronahardsurface(photoD).Ifthemufflerisdamagedorlargequantitiesofsootcannotbedislodged,replacethemufflerwithoriginalmanufacturer’sparts.Ifthemufflerisingoodcondition,reattachit.

3.Don’tovertightenthenewmuffler.Ifalockringisused,installitusingahammerandpinpunch.NOTE:Thesmoothsideofthelockringmustbeagainstthecylinderinaluminum-blockengines.Thetoothsidemustbeagainstthecylinderincast-ironengines.

4.Brushtheentireareatoclearawaydirtanddebris.Ifleftonthemuffler,driedgrassclippingsandotherdebriscancatchfireonthehotsurfaceofthemuffler.

REMOVINGARUSTYMUFFLER

Averyrustymufflermaycollapseorcrumbleasyoutwistitwithawrench.There’snoharmdoneaslongasyoutakecarenottodamagemufflermountingthreadsintheengineblockorothermufflerfittingsontheengine.Ifyourmufflerscrewsintotheengine,cutthemufflerbodyoffwithmetalsnips.Then,graspthestemusingslip-jointpliers,andunscrew(photoE).Ifthemufflerbreaksoff,leavingaconnectingpipeattachedtotheengine,graspthepipewithslip-jointpliersandunscrew(photoF).

AdvancedRepairs

ThesystemsandtechniquesinthissectionaremorecomplexthanthosedescribedintheBasicRepairsection,butthey’rewellwithinyourreachnowthatyouhavesomeprimaryrepairprojectsinyourrepertoire,asthesamebasicprinciplesapply.Ifanadvancedrepairtaskisnewtoyou,startbyreviewing“Troubleshooting”(OLDpages60to61)and“Safety”(OLDpages12to13).

Hereareafewofthesubjectsyoushouldreviewtopreparefortheprojectsinthissection:

•Beforeyoucleanyourcarburetor,reviewthebasicsofcarburetoroperation(see“FuelSystem,”pages38to41).

•Beforeyoureplacetheignition,youshouldhavesomeknowledgeofhowelectricityisgenerated(see“IgnitionSystem,”pages20to21).

•Beforeremovingcarbondeposits,it’shelpfultounderstandthesourceofcarbondepositsintheengine(see“CompressionSystem”and“FuelSystem,”pages12to19,and“Lubrication&CoolingSystem,”pages22to24).

•Beforeservicingthevalvesina4-strokeengine,reviewthemechanicsofcompression(see“CompressionSystem,”pages12to16).

•Beforeservicingabrakeorstopswitches,reviewtheprinciplesoftheflywheelbrake(see“BrakingSystem,”page26).

Thebackgroundprovidedinthesesystemsectionswillhelpyougetthroughtheadvancedrepairsprojectswithnotrouble.Ifyou’reconcernedaboutspecialissuesthatpertaintoyourengine,contactanauthorizedservicedealer.Thetechnicianstherecanofferyouhelpfuladvicespecifictoyourenginemakeandmodel.

Ifyouhaveexperienceinbasicrepairandconfidenceinyourability,youcantakeonthesetasksbyyourself:

InspectingtheFlywheel&Key

OverhaulingtheCarburetor

TestingtheElectricalSystem

ReplacingtheIgnition

ServicingtheValves

RemovingCarbonDeposits

ServicingtheBrake

THEABANDONEDTRASH-DAYLAWNMOWER

It’samazingwhatsomepeoplewillthrowout!Foroutdoorpowerequipmentbuffsonabudgetorwithapenchantforrevitalization,mowerswheeledtothecurbtoawaittheirswan-songridetothedumprepresentagreatopportunitytoexerciseyourskillsinadvancedrepair.

Upscaleneighborhoodsoftenholdthebiggestselectionofprematurelydisposedoflawnmowers.Buttherearefolksatallkindsofaddresseswhogetsomethingnewandconsidersellingtheiroldgeartobetoomuchhassle.Duringafewweeksrecently,Inotedfivesuchrejectedmachineswithinamileofmyhome.Admittedly,twoweretruegoners,butone—with2-strokepowerandmostofitsoriginallightgreenpaintstillgleaming—lookedsogoodthatIhadtoconsultitsownerastowhethertheunitwastrulyboundfortherecycler.“Takeit!”hewelcomedwithanenthusiasticgesture.Thefellowthenpointedtoits4-strokerecentreplacementandexplainedthathewassimplytiredofhavingtomixgasandoilforhisformermower.

Anotherimminentinmateofthelandfillgotquicklyrescuedwhenapasserbyascertaineditsonlyproblemwasafaultydrivemechanism.“Wow!Theengineanddecklookgreat!”thedelightedfinderexclaimed,“EvenifIcan’tgetthewheel-drivetoengage,”henotedwhileheadingawaywithhistreasure,“Icanalwaysuseitasapushmower.”

Becausetimeisoftheessencewhenspottingamoweramongstthegarbagecans,thefollowinglistisdesignedformakingaquickthumbs-upordown:

•Engagetherewindstarter.Doesthepistonmovefreelyinthecylinder?Istheresufficientcompressionordoesasharppullfeelweak?Hearanyclunksorroughness?Mighttheenginebrakestillbeengagedevenwiththebailintheoperatingposition?Ifso,seeifit’sjustacableissue.Ifitpullshardornotatall(andtheissuecan’tbeattributedtoastuckrewind)walkaway.

•Checktheoilona4-stroke.Isthereany?Isitdirty/pitchblack?Someisbetterthannone,butpresence,color(thelighter/cleanerthebetter),andthehopefulabsenceofwaterarevalidindicatorsofpastcare.

•Checkthefuel.Waterinthefuelisn’tagoodsignofthemower’shistory,butitstypicallynota“deal-breaker”onafree(orbargain-pricedgaragesale)mower.GetridoftheH2Oassoonasyougetithome.

•Lookcarefullyatthedeck.Isthereanyfatalrust-through(especiallywherethe

wheels,engine,andpushhandleconnecttothedeck)?Areallofthewheelsintact?

•Checkunderthedeck.Obviouslybentandseverelynickedbladesserveastell-talestothemachine’suse.Thecleanertheunderside,thebetterownercarethemowerenjoyed.Iftheareaundertheengineisoily(unlessthemuffleroutputsthere),there’sprobablyaseal/bearingissue.Stayclearofthatmower!Thesameassessmentappliesforanysignsofabentcrankshaft(onwhichthebladeisattached).Checkforthismajornegativebyfirstremovingthesparkplugwireandthentippingthemowersothecrankshafttravelcanbenotedbycarefullyrotatingtheblade.

•Checkforspark.IfallelseisOK,removethesparkplug,reattachthesparkpluglead/wire,andwiththebaseofit(wherethethreadsare)touchingtheengineblock,engagethestarterwhilelookingforasparkattheelectrodeinthebottomoftheplug.Somesmall-enginehobbyistsfiguretheignitionsystemwillneedattentionanyway,sodon’tbotherwiththistestonanotherwise“clean”motoruntiltheygettheirfindhome.(Note:Muchofthistestregimenappliestootherforlornoutdoorpowerequipmentleftforthesanitationdepartmentcrew.)

—P.H.

OverhaulingCarburetorsMostcarburetorproblemsarecausedbydirtparticles,varnish,andotherdepositsthatblockthenarrowfuelandairpassagesinside.GasketsandO-ringsarealsocommonsourcesofproblems.Theyeventuallyshrink,causingfuelandairleaksthatleadtopoorengineperformance.

Ifyou’redoingarebuild,you’llneedtopurchasetherepairkitforyourcarburetor,whichincludesreplacementgasketsandothernecessaryparts.Whileyou’reatit,checkthepriceofacompletereplacementcarburetorforyourengine.Insomecases,itmaybemorecost-effectivetoinstallanewone.

Ifyoudecidetorebuild,youwillalsoneedcarburetorcleaner,acleanworksurface(preferablytoppedwithasheetofwhitecardboardtoenhanceseeingremovedparts,etc.),and,ideally,asourceofcompressedairforblowingoutlooseneddebrisandsolvent.Well-equippedshopsmighthaveasmallsoniccleaningtank,asalsofoundinsomejewelrystoresforsafelyshakingloosetinybitsofdirtfromrings,necklaces,andwatchmechanisms.

Thedesignofyourcarburetordependsonthesizeoftheengineandtheapplication.Enginesdesignedforlawntractorsrequireapreciselytunedcarburetorwithachokeandidlemixturesystem.Walk-behindmowerenginesoperatewellwithoutthesedesignenhancements.Thissectionoffersdirectionsforcleaningandadjustingarangeofcarburetortypes.Yoursmaylookdifferentandmayrequirefewersteps.

Thepartsfoundinatypicalcarburetorrebuildkit.

Tools&Materials

•Boxwrenches

•Carburetorcleaner•Carburetorrepairkit•Compressedair•Enamelnailpolish•Fuellineclamp•Hammer•5/32-inchpinpunch•Screwdrivers(standard,carburetor-type)•Torquewrench

Timerequired:90minutes

PARTSOFTHECARBURETOR

REMOVINGTHECARBURETOR

1.Disconnectthesparkplugleadandsecureitawayfromthesparkplug.Then,removetheaircleanerassembly.

2.Turnoffthefuelvalveatthebaseofthefueltank.Ifyourenginedoesnotcontainafuelvalve,useafuellineclamptopreventfuelfromdrainingoutofthetankwhilethecarburetorisdisconnectedfromtheengine.

3.Somecarburetorscontainanelectricaldeviceatthebaseofthefuelbowltocontrolafterfire.Disconnectthedevice,knownasananti-afterfiresolenoid,byremovingthewireconnectorfromthesolenoid’sreceptacle.

Withthecarburetorstillconnectedtothegovernor,unfastenthecarburetormountingbolts.Ifaconnectingpipejoinsthecarburetortotheengineblock,firstremovethepipemountingbolts.Then,disconnectthecarburetorfromthepipebyremovingthenutsandslidingthecarburetoroffthestuds.

4.Sketchorphotographthegovernorspringpositionsbeforedisconnectingthemtosimplifyreattachment.Then,disconnectthegovernorspringsandremovethecarburetor,takingspecialcarenottobendorstretchlinks,springs,orcontrollevers.Linkageremoval(fromgovernororcarburetor)canbeespeciallyfrustratingifnotdonewithacalmattitudeandtheunderstandingthatitmighttakeafewminutestodecipherthe“puzzle”ofhowthestuffwasoriginallyinstalled.Sometimesthebendsneededforsuccessfullinkageappeartobeoneofthose,“Youcan’tgettherefromhere,”typeofconundrums.Evenso,abitofpatientstudyandexperimentingalmostalwaysproducesthesolution.

DISASSEMBLINGAFLOAT-TYPECARBURETOR

Yourcarburetorcontainsasmallamountoffuel.Prepareacleanbowltocatchdrippingfuelandstoresmallparts.Duringdisassembly,inspectthebowlfordirtanddebristodeterminetheconditionofyourcarburetor.

1.Removethefuelbowlfromthecarburetorbody.Thefuelbowlmaybeattachedwitheitheraboltorthehigh-speedmixturescrew.

2.Pushthehingepinoutofthecarburetorbodywithasmallpinorpinpunch.Takecaretotaponlythepintoavoiddamagingthecarburetorbody.

3.Removethefloatassembly,inletneedlevalve,andfuelbowlgasket.

WORKINGWITHSOLVENT

Carburetorcleanerisapowerfulsolventthatcaneatupordistortcarburetorparts—especiallyplasticparts—iftheyaresoakedfortoolong.Acarburetorshouldbesoakedfornomorethanfifteenminutes.Rubberparts,suchasseals,O-rings,andpumpdiaphragms,shouldneverbeexposedtocarburetorcleanerandshouldalwaysberemovedbeforesoaking.

Usecompressedairandcarburetorcleanertoclearcloggedpassagesortinymeterholesinthecarburetor.Itmaybetemptingtoreamordrilltheseholesandpassages.Neverdoso.Theyarepreciselysizedandmaybepermanentlydamagedifanysolidmaterial,suchasawireordrillbit,isinserted.

4.Ifyourcarburetorcontainsanidlemixturescrew,removeitalongwiththespring.

5.Rotatethethrottleplatetotheclosedposition,removethethrottleplatescrewsandthethrottleplate.

6.Removethethrottleplateshaftandfoamseal.Then,removethechokeplateandchokeshaftandfeltorfoamwasherinthesamemanner.

7.Useyourcarburetorrepairkittoidentifyreplaceablewelchplugs.Thesesealscoveropeningsinthecarburetorleftoverfrommachining.Insertasharpened5/32-inchpinpunchattheedgeofeachplugtoberemovedandtapcleanlytofreetheplug.

8.Unscrewthemainjetfromthesideofthecarburetorpedestal(ifequipped).Then,unscrewtheemulsiontube;itmaybescrewedintight.Acarburetorscrewdriveristhebesttoolforthejob.It’sdesignedtofittheslotintheheadoftheemulsiontubesothatyouwon’tdamagethethreadsinsidethepedestalorthetubeitselfasyouloosenit.

9.Removetheemulsiontube.

INSPECTTHECARBURETOR

Soakmetalandplasticcarburetorpartsinall-purposepartscleanerfornomorethanfifteenminutestoremovegrit.Or,wearingsafetyglasses,spraythepartswithcarburetorcleaner.Then,wipeawaysolventandotherresiduethoroughly,usingacleancloth.Neverusewireortools.Theycandamageorfurtherobstructpluggedopenings.

Inspectallcomponentsanduseadditionalcarburetorcleanertoloosenstubborngritandtoclearobstructions.

Replaceanypartsthataredamagedorpermanentlyclogged.

INSPECTINGMIXTURESCREWS

Brassmixturescrewscontroltheair-fuelmixtureathighspeedandatidle.Overtighteningcandamagethetipofthescrewsothatproperadjustmentisnolongerpossible(photoA).Removeanynonmetalpartsandsoakmixturescrews

incarburetorcleanerforfifteenminutes.Then,inspectthemcarefullyforwear.Replaceamixturescrewifthetipisbentorcontainsaridge.

COMPENSATINGFORHIGHALTITUDE

Smallenginesaresetatthefactorytooperateataverageatmosphericpressure.If

youliveatahighaltitude,youmayneedtomodifythecarburetortoensureadequateairorfuelintake.Dependingonyourmodel,youwillneedtoremovethesmallmetalfittingnearthechokeplate,knownasthemainjetairbleed(photoB)orreplacethefixedmainjet(photoC)withonedesignedforhighelevations.Askyourauthorizedservicedealerforadditionaldetailsonthenecessaryadjustmentsforyourarea.

REASSEMBLINGTHECARBURETOR

Installnewwelchplugsfromyourrepairkit,usingapinpunchslightlysmallerthantheoutsidediameteroftheplug(photoD).Taponthepunchwithahammeruntiltheplugisflat(strongblowswiththehammerwillcausetheplugtocave

in).Then,sealtheoutsideedgeoftheplugwithenamelnailpolish.

Assemblethechokebyinsertingthereturnspringinsidethefoamsealandslidingthespringandsealassemblyontothechokeshaft.Plasticchokeplateshaveastopcatchatoneendofthespring;metalplateshaveanotchtoholdthehookatoneendofthespring.

Insertthechokeshaftintothecarburetorbodyandengagethereturnspring.Ifthechokeleverusesadetentspringtocontrolthechokeplateposition,guidethespringintothenotchedslotonthechokelever.Placethechokeplateontheshaft

withthesinglenotchontheedgetowardthefuelinlet.Liftthechokeshaftandleverupslightlyandturncounterclockwiseuntilthestopontheleverclearsthespringanchor.Pushtheshaftdown.

Insertthechokeplateintothechokeshaftorattachitwithscrewssothatthedimplesfacethefuelinletsideofthecarburetor.Thedimpleshelpholdandalignthechokeshaftandplate.

Installthethrottleshaftsealwiththesealinglipdowninthecarburetorbodyuntilthetopofthesealisflushwiththetopofthecarburetor.Turntheshaftuntiltheflatsideisfacingout.Attachthethrottleplatetotheshaftwiththescrewssothatthenumbersonthethrottleplatefacetheidlemixturescrewandthedimplesfacein.

Installtheinletneedleseatwiththegroovedown,usingabushingdriver.Then,installtheinletneedleonthefloatandinstalltheassemblyinthecarburetorbody.

Insertthehingepinandcenterpin.Then,installtherubbergasketonthecarburetorandattachthefuelbowl,fiberwasher,andbowlnut.

ATTACHINGTHECARBURETORANDAIRCLEANERASSEMBLY

Positionthecarburetorsothebevelededgefitsintothefuelintakepipeandattachthecarburetorwithnutsorbolts,asrequired(photoE),leavingthesefastenerslooseforfinaltighteningwithatorquewrench.Consultyourauthorizedservicedealerforthepropertighteningtorque.

Installtheaircleanerassembly,makingcertainthatthetabsonthebottomoftheaircleanerareengaged.

InspectingtheFlywheel&KeyTheflywheelonyoursmallenginewasoriginallydesignedtostorethemomentumfromcombustiontokeepthecrankshaftturninginbetweentheengine’spowerstrokes(see“CompressionSystem,”pages12to13).Buttheflywheelontoday’ssmallenginesservesseveralotherpurposes.Thefinshelpcooltheenginebydistributingairaroundtheengineblock(see“Lubrication&CoolingSystem,”pages22to24).Thefinsalsoblowairacrosstheairvaneonapneumaticgovernor,maintainingthedesiredenginespeed(see“GovernorSystem,”page25).Magnetsmountedintheoutsidesurfaceoftheflywheelarerequiredforignition(see“IgnitionSystem,”pages20to21).Andonengineswithstartermotors,lightsorotherdevices,magnetsmountedinsideandoutsidetheflywheelareattheheartoftheelectricalsystem(see“ElectricalSystem,”page27).

Ifalawnmowerortillerbladehitsarockorcurb,theflywheelkey(left)cansometimesabsorbthedamage,reducingrepaircostssignificantly.Alwayscheckfordamagebyremovingtheflywheeltoinspectthekeyandthekeyway(theslotonthecrankshaftthatthekeyslidesinto).Thesoftmetalkeymusteliminateplaybetweentheflywheelandcrankshaft.

Tools&Materials

•File•Flywheel•Clutchtool•Flywheelpuller•Flywheelholder•Socketwrenchset

Timerequired:1hour

Theflywheelkeyisasmall,butimportant,pieceofsoftmetalmountedbetweentheflywheelandcrankshafttotimetheengine.

REMOVINGTHEFLYWHEEL

Disconnectthesparkplugleadandsecureitawayfromthesparkplug.Then,loosentheboltsholdingtheshroudinplaceandremovetheshroud.

Iftheengineisequippedwithaflywheelbrake,removeanycoveranddisconnecttheouterendofthebrakespring(photoA).

Iftheflywheelisequippedwithaflywheelclutch,removeitwithaflywheelclutchtoolwhileholdingtheflywheelwithaflywheelholderoraflywheelstrapwrench(see“SpecialtyTools,”page30).Iftheflywheelisattachedwithanut,usetheflywheelholderasabrace,andremovetheflywheelretainingnutwiththeappropriatesocket(photoB).

Withtheflywheelnutthreadedontothecrankshaft,installaflywheelpullersoitsboltsengagetheholesadjacenttotheflywheel’shub(photoC).Iftheholesarenotthreaded,useaself-tappingflywheelpullerortaptheholesusinga1/4×20tap.CAUTION:Neverstriketheflywheel.Evenaslightlydamagedflywheelpresentsasafetyhazardandmustbereplaced.

Rotatethepullernutsevenlyuntiltheflywheelpopsfree.Then,removetheflywheelandkey.

INSPECTINGTHEFLYWHEELANDKEY

Checkforcracksonyourcrankshaftorbrokenfinsontheflywheel.Replacethemifyoufindsuchdamage.Thetaperedsectionsmustbecleanandsmooth,withnoplaybetweenthetwo.

Inspectthekeywayandflywheel(photoD)fordamage.Slightburrsmayberemovedwithafile.Then,makecertainthereisnoplayorwobblingwhentheflywheelisplacedonthecrankshaft.

Inspecttheflywheelkey.Ifthereareanysignsofshearingorifyouhavedoubtsabouttheconditionofyourflywheelkey,replaceit.It’ssimpleandinexpensive.

INSTALLINGTHEFLYWHEEL

Placethenewflywheelthatyou’veobtainedfromyourauthorizedservicedealeronthecrankshaftandlookthroughtheflywheelhubtoalignthekeywaysontheflywheelandcrankshaft.

Withtheflywheelinplace,placethekeyinthekeyway;itshouldfitsecurely.

Ifyoufeelplay,checktoseeifthekeyisupsidedown.Debriscanalsopreventthekeyfromseatinginthekeyway.

Oncethekeyandflywheelaresecurelyinplace,reattachtheflywheelnutorclutch.Consultyourauthorizedservicedealerforthetorquespecificationsforyourmakeandmodel.

ReplacingtheIgnitionToday’ssmallenginescontainasolid-stateignitionarmaturemountedadjacenttotheflywheel.Theonlymovingpartsinthesystemarethemagnetsmountedintheflywheel,whichinteractwiththearmaturetoproduceelectricalcurrent.Mostignitionarmaturesaredesignedtobereplaced,notrepaired,iftheyfail.Ifyoursisanearlysolid-stateignitionarmature(say,fromthemid-1970s),itmayhavereplaceableparts.Butyou’llprobablyfindthatreplacingthearmatureistheeasiestsolutionifitfails.

Ignitionpointswereusedinsmallenginespriortotheearly1980s.Findingreplacementpartshasbecomequitedifficult.

Tools&Materials

•Benchvise•Pinpunch(3/16-inch)•Razorbladeorutilityknife•Shim•Socketwrench•Microficheorindexcards(.010inch)•Siliconesealer•Solderingiron•60/40solder•Sparkplugtester•Wirecutters

Timerequired:1hour

Solid-stateignitionarmatureshavebeenusedforsmallenginessincetheearly1980s.

Mostenginesbuiltthroughtheearly1980scontainasetofmechanicalpoints,knownasbreakerpoints,undertheflywheel.Thepointsopenandcloseanelectricalcircuitrequiredforignition.Insomecases,youcanimprovethereliabilityofsuchanenginebybypassingthebreakerpointssystemusinga

solid-stateignitionretrofitkit.It’saneasymodificationavailableatgoodsmall-engineshopsandautopartsstores.

Beforeyoureplaceasuspectignitionarmature,alwaystestignitionwithasparktester(see“ServicingSparkPlugs,”pages52to53).Checkforfaultyelectricalswitchesthatcouldbethesourceoftheproblem(see“BrakingSystem,”page26).

Thissectioncoverstheproceduresforreplacingtheignitionarmatureandbypassingabreakerpointssystemwithasolid-statesystem.

INSTALLINGANDADJUSTINGANEWIGNITIONARMATURE

Anignitionarmaturemustbesetataprecisedistancefromtheflywheel.Askyourauthorizedservicedealerforthepropergapforyourengine.Commonarmaturegaprangesare.006-.010inchand.010-.014inch.Armaturesareoftenpackagedwithashimtoassistinsettingthegap.Microficheorindexcardsoftheproperthicknessalsoworkwell.

Removetheoldignitionarmaturemountingscrews(photoA).Disconnectthestopswitchwirefromtheflywheelbrake(see“RemovingaBrakePad,”page133)andremovethearmature.

Attachareplacementarmaturefromtheoriginalenginemanufacturer,usingmountingscrews(photoA).Then,pushthearmatureawayfromtheflywheelandtightenonescrew(photoB).

Turntheflywheelsothemagnetsareontheoppositesidefromtheignitionarmature(photoC).

Placetheappropriateshimbetweentherimoftheflywheelandtheignitionarmature.Holdingtheshimandturntheflywheeluntilthemagnetsareadjacenttothearmature(photoD).

Loosenthetightscrewsothemagnetspulltheignitionarmatureagainsttheflywheelandshim.Then,tightenbothmountingscrewsandrotatetheflywheeluntiltheshimslipsfree.

TESTINGASTOPSWITCH

Insertthesparkplugleadononeendofasparktesterandattachthetester’salligatorcliptoground,suchasanenginebolt.

PlacetheequipmentstopswitchcontrolintheOFForSTOPposition.Iftheengineisnotconnectedtotheequipment,groundthestopswitchwiretothecylinder.Attempttostarttheengineusingtherewindcordorkey(ifequipped).Thereshouldbenospark.Ifasparkappears,inspectthestopswitchfordamage.Consultyourauthorizedservicedealerifyoufindafaultyswitch.

PlacethestopswitchcontrolintheRUNorSTARTposition.Iftheengineisnotconnectedtotheequipment,makesurethestopswitchwireisnotgrounded.Attempttostarttheengine.Asparkshouldbevisibleinthetester.Ifnosparkappears,checkforbrokenwires,shorts,groundsoradefectivestopswitch.

Confirmthatthestopswitchisworkingandreconnectthesparkpluglead.

RETROFITTINGANOLDERIGNITIONARMATURE

Breakerpointignitionsystemswerecommonthroughtheearly1980s.Youcanimproveignitionreliabilityonasingle-cylinderengineequippedwithbreakerpointsandatwo-legarmaturebyinstallingasolid-stateignitionconversionkitthatbypassesthepoints.Consultareputableservicedealerfortheproperconversionkit.1.Disconnectthesparkplugleadandsecureitawayfromtheplug.Then,removetheflywheelanddiscardtheoldflywheelkey.

2.Cutthearmatureprimaryandstopswitchwiresascloseaspossibletothedustcover(photoA).Then,removethedustcover,points,andplunger,andplugtheplungerholewiththeplugsuppliedintheconversionkit.

3.Loosenthescrewsandremovethearmature.Then,cutthearmature’sprimarywiretoa3-inchlength(photoB).Stripaway5/8-inchoftheouterinsulation.Then,useautilityknifeorrazorbladetoscrapeoffthoroughlytheredvarnishinsulationunderneath.Takecarenottonickorcutthewire(photoC).

4.Installtheconversionmodule(photoD).Modifytheairvanebracketsorguidesforclearance,asrequired.

5.Fastenapinpunchinabenchvise.Pushopenthespring-loadedwireretainer

bypressingdownonthepunch.Withtheslotopen,insertthearmature’sprimarywireandanewstopswitchwire(ifrequired),togetherwiththemoduleprimarywire(photoE).Then,releasethewireretainer,lockingthewiresinplace.Securethewiresbysolderingtheendswith60/40rosincoresolder.

6.Twistthearmaturegroundwireandmodulegroundwiretogether(twoturns)closetothearmaturecoil(photoF)andsolderthetwistedsection,takingcarenottodamagethearmaturecoilcasing.AvoidcrossingthesewireswiththoseinsertedinthewireretainerinStep5.

7.Removetheshortestgroundwirebycuttingitoffclosetothesolderedconnection.Cementthewirestothearmaturecoil,usingagenerousamountofsiliconsealertoprotectagainstvibrations.

8.Useascrewtoattachthearmature/modulegroundwiretothearmature(photoG).Then,fastenthearmaturetotheenginesothatthewireretaineristowardthecylinder.

9.Removetheremainderoftheoriginalstopswitchwireascloseaspossibletotheterminalontheengine.Then,routethenewwirefromthemodule,followingthesamepathastheoriginal.Fastenthenewwireinplace.Makesurethewiredoesnotinterferewiththeflywheel.

10.Installtheflywheel,usingthereplacementflywheelkeyinyourkit,andtightentheflywheelnutorrewindclutch(see“InspectingtheFlywheel&Key,”pages108to109).Setthearmatureairgap(see“InstallingandAdjustingaNewIgnitionArmature,”page111).Then,testthestopswitches(see“TestingaStopSwitch,”page111).

TestingtheElectricalSystemSmallenginesthatstartwithakeyrequireanelectricalsystemtochargethebatteryandtopoweron-boardelectricaldevices.Ifyouhearagroanorjustaclickwhenyoutrytostartasmallengineequippedwithanelectricstartermotor,yourelectricalsystemmaybethesourceoftheproblem.Electricalproblemscanalsokeepon-boardelectricaldevicesfromoperating.Thepropertestcanhelpyouidentifythesourceoftheproblem.

Whentestinganalternatororotherelectricalsystemcomponent,it’simperativethatyourmultitesterbeconnectedtotheappropriatewiresinyourengineinordertogetpertinenttestreadings.Becauseeachmodelofelectricstartingengine’selectricalsystemmaybeunique,itiswisetoconsulttheowner’s/repairmanualorserviceshop/dealerfordetailsabouttheproperwaytoattachamultitestertoyourengine/alternator.

Thissectionalsoexplainshowtoreplaceyourstator,ifnecessary.Onmostmodels,thestatorismountedundertheflywheelandisnotdifficulttoreplaceoncetheflywheelisremoved.Onsomewalk-behindlawnmowers,thestatorismountedoutsidetheflywheel,makingreplacementevensimpler.

Anautorangingmultimeterisausefuldiagnostictoolfortroubleshootingtheelectricalsysteminpowerequipment.

Tools&Materials

•Multitester•Shim•Indexcardormicrofiche•Socketwrenchset•Torquewrench

Timerequired:1hour

SELECTINGTHERIGHTTESTFORYOURALTERNATOR

Withtheengineoff,locatethethinwire(s)extendingfrombeneaththeblowerhousing.Thesewiresattachtothestatorundertheflywheelanddelivertheelectricalcurrentfromthestatortothebatteryandotherelectricaldevices.

Notethecolorofthewires(scrapeawayanyenginepainttoidentifythetruewirecolor),aswellasthecolorofthewireconnector,typicallyaninchortwofromtheblowerhousing.

Usetheappropriatetestprocedureonpage116.

BATTERYSAFETY

Smallenginestypicallyuselead-acidbatteries,whichstoreelectricalenergyusingleadplatesandsulfuricacid.Theelectrolytefluidinthebatterylosesitssulfuricacidandgainswaterasthebatteryisdischarged.

Batteryelectrolyteisextremelycorrosiveandcancausesevereburnstoeyesandskin.Ifspilledontoclothing,itwillburnholesinthematerial.Batteriesproducehydrogengasthatcancauseanexplosionifignitedbyasparkoropenflame.Minimizesafetyhazardsbyobservingtheseprecautions.•Followthemanufacturer’srecommendedprocedureforcharging,installation,removalanddisposal.

•ALWAYSholdabatteryuprighttoavoidspillingelectrolyte.•Wearprotectiveeyewearandclothingwhenhandlingbatteries.•Ifelectrolytespillsonskinorsplashesinaneye,flushimmediatelywithlotsofcoldwaterandcontactaphysicianimmediately.

•Servicebatteriesinawell-ventilatedarea,awayfromsourcesofsparksorflames.

CONDUCTINGANACVOLTSTEST

IfyourenginerequiresanACVOLTStest,setthetester’sdialtoACVOLTSandfollowthesesteps:

Inserttheblackmultitesterleadintothetester’sCOMreceptacle.Connecttheotherendtoground,suchasanengineboltorcylinderfin,ortothedoubleconnectoronthestatoroutputwires.

Inserttheredleadonthemultitesterintothetester’sACVOLTSreceptacle.Connecttheredleadtotheappropriatestatoroutputwire.

Starttheengineandletitrunforseveralminutestoreachitsoperatingtemperature.Then,usingatachometer,settheenginetestspeedandcheckthereadingonthetester.Replacethestatorifthereadingisincorrect.

Turnofftheengineanddisconnectthemultitesterfromyourequipment.

CONDUCTINGADCAMPSTEST

IfyourenginerequiresaDCAMPStest,setthetester’sdialtoDCAMPSandfollowthesesteps:

Inserttheblackmultitesterleadintothetester’sCOMreceptacle.Connecttheotherendtothebattery’spositiveterminal.(NOTE:Thebatterymustbegroundedtotheequipmentframeortheengineblocktocreateacomplete

circuit.)Inserttheredleadonthemultitesterintothetester’sAMPSreceptacle.

Connecttheredleadtotheappropriatestatoroutputwire.Starttheengineandletitrunforseveralminutestoreachitsoperating

temperature.Then,usingatachometer,settheenginetestspeedandcheckthereadingonthemultitester.Anincorrectreadingindicatesthatthestator,diodeorregulatorshouldbereplaced.

Turnofftheengineanddisconnectthetesterfromyourequipment.

REPLACINGASTATORUNDERTHEFLYWHEEL

Inmostcases,youneedtoremovetheblowerhousing,rotatingscreen,rewindclutch,andflywheeltogettothestator(see“InspectingtheFlywheel&Key,”

pages108to109).Ifyourstatorismountedoutsidetheflywheel,followtheinstructionsunder“ReplacinganExternalStator”(opposite).

Withtheflywheelremoved,notethepathofthestatorwires,underonecoilspoolandbetweenthestarterandstarterdrivehousing.

Removethegroundwireorrectifierassembly(ifequipped)fromthestarterdrivehousing.Then,removethestatormountingscrewsandbushings.

Beforeinstallinganewstator,locatethestatorwiresagainstthecylinderandmakesurethewiresremainclearoftheflywheel.

Installanewstatorassembly,makingcertaintheoutputwiresareproperlypositioned.Whiletighteningthemountingscrews,pushthestatortowardthecrankshafttotakeupclearanceinthebushing.Then,tightenthescrewsto20inch-pounds.

Reinstalltheflywheel,screenandblowerhousing.Then,attachthegroundwireorrectifierassembly(ifequipped)tothedrivehousing.

REPLACINGANEXTERNALSTATOR

Disconnectthestatoroutputwirefromwiresleadingtothebatteryorotherelectricaldevices.

Rotatetheflywheeluntilthemagnetsarepositionedawayfromthestator.Then,loosenthestatormountingboltsandremovethestatorfromtheengine.

Withtheflywheelmagnetspositionedawayfromthestator,installthenewstator,leavingawidegapbetweenthestatorandflywheel.Tightenoneofthemountingbolts.

Reattachthestatoroutputwires.Then,followtheprocedurefor“AdjustingtheAirGaponanExternalStator”(below).

ADJUSTINGTHEAIRGAPONANEXTERNALSTATOR

Thegapbetweenthestatorandtheflywheelmustbesetpreciselyforthestatortofunctionproperly.Manystatorsrequirea.010-inchstatorairgap.Consultyourauthorizedservicedealerforthepropergapforyourstator.

Rotatetheflywheeluntilthemagnetsarepositionedawayfromthestator.Loosenbothstatormountingboltsandmovethestatorawayfromthe

flywheel.Then,tightenoneofthemountingbolts.Placeashimormicrofichecardoftheproperthicknessbetweenthestatorand

theflywheel(photoA).

Turntheflywheeluntilthemagnetsareadjacenttothestator.Loosenthetightenedboltandletthemagnetspullthestatoruntilitisflush

withtheshim.Tightenbothmountingboltsto25inch-pounds(photoB).

Turntheflywheelwhilepullingontheshimtoreleaseit.

RemovingCarbonDepositsOnebyproductofcombustioniscarbon,theblacksootthatcancollectandhardenonthecylinderhead,cylinderwall,piston,andvalves.Carbondepositsinthecombustionchambercanaffectengineperformance,resultinginhigheroilconsumption,engineknocking,oroverheating.

Itisprudenttoremovethecylinderaftereach100hoursofoperationandscrapeoffthecarbon,usingthetoolsandsolventsdescribedinthissection.Cleanthecylindermorefrequentlyifyouuseyourengineheavily.

Carbondepositsoncriticalengineparts,suchasthecylinderheadabove,haveanegativeimpactonengineperformanceandshouldbecleanedoffevery100hoursorso.

Tools&Materials

•Cylinderheadreplacementgasket

•Nylon-facedhammer•Puttyknife•Rubbergloves•All-purposesolvent•Steelwool•Torquewrench•Wirebrush•Woodenorplasticscraper

Timerequired:2hours

Allrubbercomponentsandsomeplasticpartsaresubjecttodistortionifcarbcleanerissprayeddirectlyonthem.

REMOVINGENGINECOMPONENTS

Thefirststepinservicingthecylinderheadisreachingthecylinderhead.Youmayneedtoremovesomeothercomponentsfirst.

Removethemuffler,mufflerguard,andanyothercomponentsthatblockaccesstothecylinder.

Cylinderheadboltsnearthemufflerandexhaustportmaybelonger.Toavoidsubsequentconfusionofwhichboltgoeswhere,preparea“keeper”template.Drawaroughoutlineofthecylinderheadonapieceofcardboardandpunchholesforeachboltlocation.Then,removethecylinderheadboltsandinsertthemthroughthecorrespondingholesinthis“keeper”templateuntilyouarereadytoreinstallthecylinderhead(photoA).Inanoldorneglectedengine,cylinderheadboltsmayberustedorcorrodedanddifficulttoremovewithoutbreakage.Abrokenonerequiresdrillingandbackingoutwithastudextractortool.Often,thisalsonecessitatescleaningupthethreadsinthecylinderblock.

Liftoffthecylinderhead.Iftheheadsticks,strikeitonthesidewithanylon-facedhammer.Thisshouldloosenthecylinderheadenoughforyoutogentlylift

itofftheengine.NOTE:Donotpryoffthecylinderhead.Thiscandamagethesurfaceoftheengineblockorthecylinderhead.

Removeanddiscardtheoldheadgasket(photoB).

REMOVINGCARBONDEPOSITS

Alwayswearprotectiveeyewearandsolvent-proofgloveswhenremovingcarbon.Askyourauthorizedservicedealertorecommendanall-purposesolventthatwillnotharmaluminumorplasticcomponentsorleaveunwantedresidues.

Placethepistonattopdeadcentersothatthevalvesareclosed.Then,scrapecarbongentlyfromthecylinderhead,usingawoodenorplasticscraper.Takecarenottodigthescraperintothealuminum.Onstubborndeposits,useaputtyknife,wirebrush,orsteelwool(photosA,B,andC),takingcarenottobeardownonthemetalsurfaces.

Cleanawaytheremainingcarbonwithsolvent,usingfinesteelwooltosmoothroughspots.Youcanalsosoakmetalpartsforuptofifteenminutestoremovestubborndeposits.Scrapeagain,ifnecessary,toloosenstubborngrit.Then,cleantheareathoroughlywiththesolventandsettheheadaside.

Withthepistonstillatthetopofthecylinderandthevalvesclosed,usethesamemethodtoremovecarbondepositsfromthepistonandtheendofthecylinder(photoC).Notethatpistonsinmost2-strokeengineshaveanexhaustdeflector“crown”andarenotaseasytoscrapecleanasaflat4-strokepiston.Somerepairshops’policyistoremoveshapedpistonsforcleaningonawirewheel.

Turnthecrankshafttoopeneachvalve,andcarefullyremoveanyvisiblecarbondepositsonthevalvesandvalveseats(photoD),usingonlyabrasswirebrush.CAUTION:Donotallowgrittofallintothevalvechambersorbetween

thepistonandthecylinderwall(photoE).

Inspectthevalvesandvalveseatstoseeiftheyarecracked,rough,orwarped.Bringdamagedpartstoanauthorizedservicedealerforinspectionbeforereassemblingthehead.

Usingascraper,solvent,orboth,removeanyremainingcarbonandresidueleftbehindbytheheadgasketonthecylinderheadandengineblock.Cleanthesurfacesthoroughlybeforeinstallingthenewheadgasket.Anydebrisoroilleftonthecylinderheadorengineblockmaypreventatightsealandcauseeventualenginedamage.

REASSEMBLINGTHECYLINDERHEAD

Inspectthesurfacesoftheengineblock,cylinderhead,andnewheadgaskettobesuretheyareclean.

Placethenewheadgasketinpositionontheengineblock.Donotusesealingcompounds.

Setthecylinderheadontheheadgasket,aligningthecylinderheadwiththegasketandtheengineblock.

Removeeachheadboltfromitsholeinthecardboard“keeper”template.Removinganyrust,corrosion,orcarbonizeddirtfromthemwithawirebrushatthistimeisagoodpractice.Then,priortoreinstallingtheboltsthroughthecylinderheadandintotheblock,lightlyoilthemandreinserttheboltsintopositionusingfinger-turning,atfirst,toavoidcross-threading.Leaveeachboltabitlooseandreadyforfinaltighteningwithawrench.Makesuretoattachanyhousingsorbracketsthatareheldinplacebytheheadbolts.

Usingawrench,tightenthecylinderheadboltsuntileachoneisjustsnug.Thisisbestaccomplishedina“criss-cross”fashionwhere,aftertighteningaboltononesideofthehead,younexttackletheoneoppositeitinordertokeepanevenpressureonthematingsurfaces.Forfinaltightening,useatorquewrench.Proceedinincrementsofroughlyone-thirdthefinaltorque.Consultyourowner’smanualforthefinaltorque“criss-cross”sequenceandtorquingspecifications.Avoidtighteningasingleboltallthewaybeforetighteningtheotherbolts,otherwisethisuneventighteningislikelytowarpthecylinderhead.

ServicingtheValvesValvescontroltheflowoffuelvaporintothecombustionchamberandtheflowofexhaustgasesleavingtheengine.Faultyordirtyvalvesmaystickandcandeveloppits,cracks,orgroovesthatcausetheenginetolosepowerandfuelefficiency.

Whenyouremovethevalvesfromtheengine,inspectthemcarefully.Then,ifthevalvesarenotbadlywornandthepartsarenotdamaged,youcantuneupthevalvesandseats(see“LappingtheValves,”page127)sothatthevalvessealeffectively.

Valvescontainastem,neck,head,andface.Eachvalvestemmovesinavalveguidethatismachineddirectlyinthecylinderblockorinareplaceablebushing.Eachvalvealsomovesthroughavalvespring,adjacenttotheguide,thatpushesthevalvetowardtheclosedpositionandholdsthevalvefaceagainstthevalveseat.Eachvalvespringisheldinplacebyavalvespringretainer.Somevalveassembliesalsoincludearotator,acircularcomponentthatturnsthevalveslightlyineachcycletoensureasymmetricalwearpatternonvalvesandseats.Valvesareopenedbytappetsthatrideonthecamshaftinsidethecrankcase.

Small-enginevalvesarenotbigbuttheirjobisveryimportant.Atypicalassemblyincludesthevalve,valvespring,valverotator,andvalvespringretainer.

Tools&Materials

•Feelergaugeset•Hexwrenchset•Needlenosepliers

•Nutdriverset•Calipers•Safetyeyewear•Socketwrenchset•Torquewrench•Lappingcompound•Valvelappingtool•Valvespringcompressor

Timerequired:90minutes

AvalvespringcompressorisanessentialtoolforremovingandinstallingvalvesonL-headenginesandsomeoverheadvalveengines,bothofthe4-stroketype.

Thissectioncoverstheproceduresforremoving,inspecting,cleaning,andreplacingvalvesandrelatedparts.

VALVEDESIGN

Valvedesignforthe4-strokesmallengineincludesoneintakevalveandoneexhaustvalvepercylinder.Thediagramsonthispageshowthepartsoftypicalvalvesindetailandtheirlocationsintheengine.

Intakevalvesopentoallowtheair-fuelmixturetoenterthecombustionchamber.Exhaustvalvesopentoallowspentfuelgasestoleavetheengine.Both

valvesclosetosealthecombustionchamberforthepiston’scompressionstroke.Valvespringspushthevalvestowardtheclosedposition,sothattheyopen

onlyatpreciselytimedintervals.Thevalvesarepushedopenbytappetsthatrideonthelobesofthecamshaft.Thecamshaftturnsalongwiththecrankshaft;botharedrivenbythemovementofthepiston.Thissynchronizestheactionsofthevalveswiththoseofthepiston.

InL-headengines,thevalvesarelocatedtoonesideofthecylinder.Thevalvestemsrunthroughthecylinderblock,paralleltothepiston.

Inoverheadvalveengines,thevalvesarelocatedinacylinderheadthatismuchlargerthanthatfoundinanL-headengine.Overheadvalvesarepushedopenbypivotingrockerarms,operatedbypushrods.Thepushrods,inturn,arepushedtowardtherockerarmsbythetappets.Theslightlymorecomplexdesignyieldsgreaterpower.

L-Head

Overheadvalve(OHV)

MACHININGVALVES

Thevalvesonyour4-strokeenginemaystillfunctionafteryearsofservice—withnobent,cracked,ordamagedparts.Butinalllikelihood,theyarewornandnolongerformagoodsealwhenthevalvesareclosed.Theresultislossofpowerandwastedfueleachtimeyourunyourengine.

Whileafewdo-it-yourselfersobtainvalvegrindingstonesthatcanbeactivatedviaanelectricdrill,mostsmall-engineexpertsagreethatitiswiserforallbuttheexperiencedamateurmechanictotakehis/herenginetoaprofessionalshopwhereatechniciancanroutinelyrestorethevalveseatsorinstallones.Thisprowillalsohavequickaccesstoanyrequiredreplacementparts,suchasvalveseatinserts.

REACHINGTHEVALVECHAMBER

Beforeyoucanservicethevalves,removeenginecomponentsthatinterfere.NOTE:Alwayswearsafetyeyewearwhenremovingandinstallingvalves.

Removethemuffler(see“Inspecting&ChangingtheMuffler,”pages92to95),crankcasebreather(seepage59),andanyothercomponentsthatblockaccesstothevalvechamber(photosAandB).

Removethecylinderheadbolts(photoC).Labelthebolts,ifnecessary,toensureproperinstallationlater,sincetheymaybeofdifferentlengths(see“RemovingCarbonDeposits,”pages118to121).

VALVESPRINGCOMPRESSOR

Ifyouplantoremovethevalvesfromyour4-strokeengine,avalvespringcompressorisamust.Removingvalveswithoutthistoolisunsafeandcanbeanexerciseinfrustration.Themethodforusingthetoolvariesdependingonthetypeofvalveassemblyandthedesignoftheengineblock.Somevalveassembliesholdthevalvespringinplacewithapinorapairofcollar-shapedautomotive-typeretainers.Othersusearetainerwithakeyhole-shapedslotthatlocksontothevalvestem.Nomatterwhichtypeofretaineryoufindonyourvalves,avalvespringcompressorallowsyoutodothejobright.

REMOVINGTHEVALVES(AUTOMOTIVETYPEORPINRETAINERS)

Adjustthejawsofthevalvespringcompressoruntiltheytouchthetopandbottomofthevalvechamber.

Pushthetoolinuntiltheupperjawslipsovertheupperendofthespring.Tightenthejawstocompressthespring(photoD).

Removetheretainersandliftoutthevalves,compressorsandsprings.

REMOVINGTHEVALVES(KEYHOLERETAINERS)

Removingkeyholeretainersrequiressomepatience.Keepinmindtheretainer’skey-shapedslot.Thiswillhelpyousliptheretaineroffthevalvestem,evenwhentheretainerishiddenfromviewbythevalvespringcompressor.1.Sliptheupperjawofthevalvespringcompressoroverthetopofthevalvechamberandthelowerjawbetweenthespringandretainer.Iftheenginedesigndoesnotpermittheupperjawtofitoverthetopofthevalvechamber,inserttheupperjawintothechamberoverthetopofthespring,sothatthe

springisbetweenthetool’sjaws(photoE).

2.Rotatethehandleonthevalvespringcompressorclockwisetocompressthespring.Then,slidetheretaineroffthevalvebyshiftingitwithneedlenoseplierssothatthelargepartofthekeyholeisdirectlyoverthestem.Usetheplierstoremovetheretainerfromthevalvechamber(photoF).

3.Withthevalvespringcompressorclampingthespring,removethetoolandspringfromthechamber.Then,slowlycrankopenthevalvespringcompressortoreleasethetensionandremovethespring.

INSPECTINGTHEVALVES

Beforewipingorcleaningthevalves,lookthemovercarefully.Residueonthevalvesmayhelpyouidentifyaspecificproblem.Gummydepositsontheintakevalvegohandinhandwithadecreaseinengineperformance,oftenbecausetheenginehasbeenrunonoldgasoline.Harddepositsoneithervalvesuggestburningoil,whichhasseveralpossiblecauses(seepage39).Followthestepsbelowtocheckforthemostlikelysourcesofvalveproblems.

1.Checkthevalvefaceforanirregularseatingpattern.Thepatternaroundthefaceshouldbeevenwiththevalveheadandofequalthicknessallthewayaround.Then,lookforstubborndeposits.Removethemwithawirebrushandsolvent,soakingthepartsforseveralhours,ifnecessary,toloosenhardenedgrit.

2.Runafingernailorcreditcardalongthevalvestemonceyouhavecleanedit.Ifyoufeelaridge,thevalvestemiswornandshouldbereplaced.Keepinmindthatthevalveguidemayalsobewornandneedreplacementbyamachinist(see“MachiningValves,”page124).

3.Measurethethicknessofthevalvehead,knownasthevalveheadmargin,usingacaliper.Replacethevalveifthemarginmeasureslessthan1/64inch.

4.Examinethesurfacesofthevalvefaceandseat.Anunevenwearpatterntellsyouit’stimetoreplacethembothorresurfacetheseatandreplacethevalve(see“MachiningValves,”page124).Checkthatbothvalvespringsarestraight.Replaceeitherspringifitisbent.NOTE:Theexhaustvalvespringmayusethickerwirethantheintakevalvespring.

LAPPINGTHEVALVES

Youcansmoothoutminorscoringandpittingofthevalvefaceandseatandrestoreavalve’sabilitytosealthecombustionchamberbylappingthevalves.Thisprocedureinvolvesrotatingthevalveintheseatwithalayeroflappingcompoundinbetweenthevalveandseat.Alappingtoolisusedtoholdandrotatethevalve.Duringlapping,you’llneedtocheckyourprogressoften.Otherwise,itiseasytoremovenotonlythecarbonbuildup,butalsomuchofthemetal,furtherdamagingthevalveorseat.

Applyasmallamountofvalvelappingcompoundtothevalvefaceandinsertthevalveintothevalveguide.Wettheendofthelappingtoolsuctioncupand

placeitonthevalvehead.Spinthevalvebackandforthbetweenyourhandsseveraltimes.Liftthetool,rotateone-quarterturn,andspinagain.

Cleanthesurfacefrequentlyandcheckyourprogress.Laponlyenoughtocreateaconsistentandevenpatternaroundthevalveface.

Oncelappingiscompleted,cleanthevalvesthoroughlywithsolventtoensurethatalloftheabrasiveresidueisremoved.Anyparticlesthatremaincanrapidlydamagethevalvesandotherenginecomponents.

ADJUSTINGTAPPETCLEARANCES

Sincelappingremovesasmallamountofmaterialfromthesurfacesofthevalvefaceandvalveseat,youmayneedtoadjustthetappetclearances—thespacing

betweenthevalvestemandthetappet—afterlappingandreinstallingthevalves.Consultashopmanualoraskyourauthorizedservicedealerforthecorrecttappetclearanceforyourengine.

Witheachvalveinstalledinitsproperguidesinthecylinder,turnthecrankshaft(clockwiseasviewedfromtheflywheelendofthecrankshaft)totopdeadcenter.Bothvalvesshouldbeclosed.Then,turnthecrankshaftpasttopdeadcenteruntilthepistonis1/4inchdownfromthetopofthecylinder.

Checktheclearancebetweeneachvalveanditstappet,usingafeelergauge.Ifclearanceisinsufficient,removethevalveandgrindorfiletheendofthevalvestemsquaretoincreasetheclearance.Checkthelengthfrequentlyasitiseasytoremovetoomuchmetal.

Oncetheindividualvalvepartshavebeenthoroughlycleaned,lubricatethevalvestemsandguides,usingvalveguidelubricant.Then,makecertainthereisNOlubricantontheendsofthevalvestemsortappets.

VALVELIFE

Thelifeofastandardexhaustvalveisoftenshortenedbecauseofburning,whichoccurswhencombustiondepositslodgebetweenthevalveseatandthevalveface.Thesedepositspreventvalvesfromclosingandsealingcompletely.Depositsleftoverfromburningaremorecommononenginesthatoperateatconstantspeedsandconstantloadsforlongperiods,suchasgenerators.

Valvelifecanbeextendedusingavalverotator,whichturnstheexhaustvalveslightlyoneachlift,wipingawaydepositslodgedbetweenthevalvefaceandseat.Exhaustvalveswhichcanbeusedtogetherwithvalverotatorshaveagreaterresistancetoheat,socanreducethisproblem.

REINSTALLINGVALVESWITHKEYHOLERETAINERS

Youneedsafetyeyewearduringthisstep,toprotectyourselffromthepossibilityofaflyingspring.

Valveswithkeyholeretainersdonotrequireanadditionalretainer.Compressthekeyholeretainerandspringwiththecompressortool—thelargeholeshouldfacetheopeninginthetool—untilthespringissolid(photoA).

Brushthevalvestemwithvalvestemlubricant(photoB).

Insertthecompressedspringandretainerintothevalvechamber(photoC).

Insertthevalvestemthroughthelargeslotintheretainer(photoD).Then,pushdownandinonthevalvecompressoruntiltheretainerbottomsoutonthevalvestemshoulder.

Reinstallthecrankcasebreatherandothercomponents.

INSTALLINGVALVESWITHPINSORAUTOMOTIVE-TYPERETAINERS

Onceagain,safetyeyewearisabsolutelynecessary.Remember:aspringthatisundertensioncanandoftendecidestopoplooseandflythroughtheair.

Placethevalvespringintothevalvespringcompressorandrotatethetool’shandleuntilthespringisfullycompressed.

Insertthecompressedspringintothevalvechamber.Brushthevalvestemwithvalvestemlubricant(photoB).Then,lowerthe

valvestemthroughthespring(photoD).Holdthespringtowardthetopofthechamberandthevalveintheclosedposition.

Ifpinsareused,inserteachpinwithneedlenosepliers.Ifautomotive-typeretainersareused,placetheretainersinthevalvestemgroove.

Lowerthespringuntiltheretainerfitsaroundthepinorautomotive-typeretainer.Then,pulloutthevalvespringcompressor.

Reinstallthecrankcasebreatherandothercomponents.

REMOVINGOVERHEADVALVES

Overheadvalvedesignsvaryfromone4-strokeenginemodeltoanother.Thepartsandservicingstepsinyouroverheadvalvecylindermaydifferfromtheapproachthatfollows,whichisbasedona6-horsepowerAmerican-madeenginethatdoesnotrequiretheuseofavalvespringcompressor,makingvalveremovalandinstallationsimple.

Removetheaircleanerassembly,fueltank,oilfilltube,blowerhousingandrewindstarter,mufflerguard,muffler,carburetor,andanyotherpartsthatblockaccesstothecylinderhead.

Removethescrewsfromthevalvecover,usingasocketwrenchornutdriver(photoA).Then,removethevalvecover,breathervalveassembly(ifequipped),andanygaskets.

Removetherockerarmboltswithasocketwrenchornutdriver(photoB).Thenremovetherockerarmsandpushrods.

Removethevalvecaps(ifequipped).Theyareseatedonthevalvestems(photoC).

Useyourthumbstopressinonthespringretainerandvalvespringoveroneofthevalves.Withthevalvespringcompressed,removetheretainer(photoD).Ifyourengineusesakeyholeretainer,lineupthelargeslotintheretainerwiththevalvestemandreleasethespringslowlysothatthestemslipsthroughthelargeslot.Then,repeattheprocedurefortheothervalve.

Removethepushrodguideboltsandpushrodguide.Removethecylinderheadboltsandremovethecylinderheadbyrockingit

withyourhands.Ifnecessary,loosenthecylinderheadbystrikingitwithanylon-facedhammer.Neverpryitloose,asthismaydamagethehead.

Removeandinspectthevalves,guidesandseats(see“InspectingtheValves,”page126).Theintakeandexhaustvalvesoftenaremadeofdifferentsteelalloysandmaybedifferentcolors.

INSTALLINGOVERHEADVALVES

1.Checkthatvalvestemsandguidesarefreeofdebrisandburrs.Then,lightlycoatthevalvestemswithvalveguidelubricantandinserttheminthecylinderhead,takingcaretoplacethecorrectvalveineachvalveguide.

2.Placethepushrodguideonthecylinderheadandattachthemountingbolts,usingatorquewrench.Coattherockerarmstudthreadswithahardeningsealantandinstalltherockerarmstuds,usingasocketwrench.Consultyourauthorizedservicedealerforthepropertorquesettingsforthemountingboltsandstuds.

Lubricatetheinsidediameterofeachvalvestemseal(ifequipped)withengineoilandinstallthesealsonthevalvestems.Pressthemintoplace.

3.Installavalvespringandretainerovereachstem.Useboththumbstocompressthespringuntilthevalvestemextendsthroughthelargeendofthekeyholeslot.Checkthattheretainerisfullyengagedinthevalvestemgroove.Repeatthisstepfortheothervalve.

Coatthethreadsofthecylinderheadboltswithvalveguidelubricant.Installanewcylinderheadgasketonthecylinder,inserttheboltsinthecylinderandpositionthecylinderheadonthecylinder.

4.Tightenthecylinderheadboltsinincrements,usingatorquewrench.Turneachboltafewturns,thenproceedtothenextboltuntileachboltisjustsnug.Then,forfinaltightening,proceedinincrementsofroughlyone-thirdthefinaltorque.Consultyourowner’smanualforfinaltorquespecifications.Uneventighteningislikelytowarpthecylinderhead.

Installthepushrodsthroughthepushrodguidesandintothetappets.

5.Installthecapsontheendsofthevalvesandwipeawayanylubricant.Then,installtherockerarmassemblieswhileholdingtherockerarmsagainstthevalvecapandpushrod.

Rotatetheflywheelatleasttworevolutionstobesurethepushrodsoperatetherockerarms.

ADJUSTINGOVERHEADVALVES

1.Releasethebrakespring.Then,turntheflywheeltoclosebothvalves.

Insertanarrowscrewdriverintothesparkplugholeandtouchthepiston.Turntheflywheelclockwisepasttopdeadcenteruntilthepistonhasmoveddown1/4inch.Usethescrewdrivertogaugethepiston’srangeofmotion.

2.Checkthevalveclearancebyplacingafeelergaugebetweenthevalveheadandtherockerarm.Clearancesdifferforthetwovalvesandtypicallyrangefrom.002-.004inchto.005-.007inch.Askyourauthorizedservicedealerforthepropervalveclearancesforyourmakeandmodel.

Adjusttheclearancesasrequiredbyturningtherockerscrew.Onceadjustmentsarecompleted,tightentherockernut.

Installthevalvecover,usingnewgaskets,asrequired,andmakesurethecoverissecure.

ServicingtheBrakeAwell-maintainedbrakingsystemshouldstoptheengineandanyattachedcuttingequipmentwithinthreesecondswheneveryoustepawayfromtheequipmentorreleasethebrakebail.Abrakebailisstandardequipmentontoday’smowers,tillers,andotherwalk-behindequipment.Thestopswitchimmediatelygroundstheignition,shuttingofftheengine,whileabrakepadorbandstopstheflywheelfromspinning.

Iftheengineoperatesformorethanthreesecondsafterthebailisreleased,thestopswitchmaybefaulty.Ifthebladespinsformorethanthreeseconds,thebrakepadorbandmaybewornorinneedofadjustment.Many21stCentury-builtmodelsuseabrakepadthatrequiresnoadjustment.Someoldermodelsuseabrakeband,whichmayrequireadjustmentbyanauthorizedservicetechnician.Thissectioncoversthereplacementproceduresforthebrakebandandpadstyles.

Thebrakingsystemonasmallengineemploysacaliperandpadtostoptheflywheelwhenthebrakeisactivated.

Tools&Materials

•Caliper•Multitester•Needlenosepliers•Socketwrenchset•Starterclutchadapter(forsomemodels)•Tangbendingtool•Torquewrench

Timerequired:1hour

Mostsmall-engineequipmentisequippedwithabrakebailforyoursafety.Thebrakebailisdesignedtoprotectyoubystoppingtheengineandanycuttingequipmentanytimeyoureleaseit.Temptationstotie-wrap,tape,orvelcrothebrakebailtothemowerhandleshouldbestronglyresisted!

REMOVINGABRAKEPAD

1.Removethesparkplugleadandsecureitawayfromthesparkplug.Then,removeanyothercomponentsthatblockaccesstothebrake,suchasthefingerguard,fueltank,oilfilltube(left),blowerhousing,orrewindstarter(right).

2.Removethebrakecontrolbracketcover,ifequipped.Then,loosenthecableclampscrewandremovethebrakecablefromthecontrollever.

3.Disconnectthespringfromthebrakeanchor,usingneedlenosepliers.Then,removethestopswitchwirefromthestopswitchbygentlysqueezingtheswitchandpullinglightlyonthewireuntilitslipsfree.Iftheengineisequippedwithanelectricstartermotor,disconnectthepairofwiresleadingtothestartermotor.Loosenthebrakebracketscrewsandremovethebracketfromthebrakeassembly.

INSPECTINGANDTESTINGABRAKEPADSYSTEM

Inspectthebrakepadfornicks,cuts,debris,andotherdamage.Checkforwear,bymeasuringthepad’sthicknesswitharulerorcaliper(photoA).NOTE:Measurethepadonly,notthebracket.Replacethebrakeassemblyifthepad’sthicknessislessthan.090inch.

Testthestopswitch,usingamultitesterorohmmeter,todeterminewhethertheignitioncircuitisgroundedwhenthestopswitchisactivated(photoB).Thestopswitchshouldshowcontinuity(0ohms)toenginegroundwhentheswitchissettoSTOP,andnocontinuity(∞),whentheswitchissettoRUN.Ifyouidentifyaproblem,checkforlooseorfaultyconnections.

REASSEMBLINGTHEBRAKINGSYSTEM

Installthebrakeassemblyonthecylinder(photoC).Tightenthemountingboltsto40inch-pounds,usingatorquewrench.

Installthestopswitchwire,bendingtheendofthewire90degrees(photoD).

Installtheblowerhousingandanyotherenginecomponentsremovedforbrakeservicing.

Checkthebrakingactionbypivotingthelever.Makesurethelevermovesfreelyandthepadmakesfullcontactwiththeflywheel.

Attachthebrakespring,usingneedlenosepliers,andconnectthebrakecablethatconnectstothebrakebailonyourwalk-behindequipment.

Testthebrakingsystembystartingtheengineandthenreleasingthebrakebail.Theengineandthebladeorotherequipmentshouldcometoastopwithinthreeseconds.Ifyouareuncertainabouttheeffectivenessofyourbrakingsystem,bringtheequipmenttoyourauthorizedservicedealerforfurtherinspection.

BRAKESAFETY

Theonlysafewaytousethebrakebailonyoursmall-engineequipmentistopullandholdthebailbyhandwhenstartingandrunningtheengine.Youcanreleaseitwhennecessarytostoptheengine.Keepingthebailintheoperatingpositionbyanyothermeansoverridesanimportantsafetymechanism.Thebailisrequiredbylawonanymowersoldaftertheearly1980sandisdesignedtoprotectyoufrominjury.

REMOVINGANDINSPECTINGABANDBRAKE

Thebrakebandcontainsloopsateitherend,mountedonastationaryandamovablepost.Atangoverthemovablepostpreventsthebrakebandfromdislodgingduringoperation.

1.Useatangbendingtool(see“TangBendingandOtherAdjustmentMethods,”pages88to89)tobendthecontrollevertangoutwardsoitclearsthebandbrakeloop.

2.Releasethebrakespring,usingpliers.

3.Liftthebandoffthestationaryandmovableposts.Inspectthebandfordamage.Replaceitifyoufindnicksorcuts.

4.Checkforwear,bymeasuringthepad’sthicknesswitharulerorcaliper.NOTE:Measurethepadonly,notthemetalband.Replacethebrakebandifthepad’sthicknessislessthan.030inch.

TESTINGABANDBRAKE

Testthebandbrake’sstoppingpowerwiththesparkplugleadsecuredawayfromthesparkplug.Onelectricstartengines,disconnectandremovethebattery.

Withthebrakeengaged,turnthestarterclutch,usingastarterclutchadapterandtorquewrench.Turningtheflywheelclockwiseatasteadyrateshouldrequireatleast45inch-poundsoftorque.Ifthetorquereadingislower,

componentsmaybeworn,damaged,orinneedofadjustment.Testthestopswitch,usingamultitesterorohmmeter,todeterminewhether

theignitioncircuitisgroundedwhenthestopswitchisactivated.Thestopswitchshouldshowcontinuity(0ohms)toenginegroundwhentheswitchissettoSTOP,andnocontinuity(∞)whentheswitchissettoRUN.Ifyoudiscoveraproblem,checkforlooseorfaultyconnections.

ASSEMBLINGABANDBRAKE

Reinstallthestopswitchwireonthecontrolbracket.Onoldersystems,reinstallthestopswitchwireonthecontrolbracketstopswitchterminal.

Placethebandbrakeonthestationarypostandhookitovertheendofthemovablepostuntilthebandbottomsout.NOTE:Thebrakematerialonasteelbandmustbeontheflywheelsideafterassembly.Onoldersystems,installthebandbrakeonthestationaryandmovableposts.

Bendtheretainertanguntilitispositionedoverthebandbrakeloopsothattheloopcannotbeaccidentallydislodged.Afterassembly,checkthatthebrakingmaterialonthemetalbandfacestheflywheel.

2-StrokePowerEquipmentIna2-strokeengine,thepistonactsasavalve,exposingtheintakeandexhaustportsatdesignatedmomentsinthecycle.Two-strokeenginesarestillwidelyusedforchainsaws,leafblowers,andotherhand-heldequipment.Theyarealsocommonforoutboardmotorsandmotocrossmotorcycles.Theyarenolongerusedonstreetbikesinmanycountriesbecauseofolder2-strokeengines’higheremissions.

Two-strokeengineshavelongbeenpreferredforhand-heldequipmentbecauseoftheirlightweightdesign.Thesamefiveevents(intake,compression,combustion,power,andexhaust)thatoccurina4-strokeengineoccurusingfewerparts.However,thelatesttechnologyhasreducedtheweightof4-strokeenginecomponents,creatingthepotentialforinroadsinthehand-heldequipmentindustry.

Technologicaladvancesingasandoilinjection/computerizedignitionhavealsobenefited2-strokeenginedesign,withsomecontemporaryoutboardmotors,forexample,burningtheirfuelandrecombustingrelatedexhaustsocompletelythatresultingemissionsarelessthanthatoftheir4-strokecounterparts.

2-STROKETHEORY

Two-strokepowerplantsaresimpler,havefewermovingparts,andareoftenlighterthantheir4-cyclesisters.Theygeneratepoweroneverytwostrokes(oneuptocompressandignitethefreshfuel/airandthen,pushedbytheresultingexplosion,onedowntouncoverportsforexhaustescapeandotherportstoletinafreshchargeoffuel/air)ofpistontravel.

Many2-strokeengineshaveareedvalvebetweenthecarburetorandcrankcasethatactsasatinysafetydoor—operatedbycrankcasevacuumpressure—lettingfreshfuel/airintothecrankcasetoawaititssubsequententrythroughthecylinderports,whilepreventinganyfuel/airfromescaping.Ina2-strokemotor,crankcasepressureisespeciallyimportant.That’swhyalloftheengine’srequisitesealsandmatingsurfacesmustbeasairtightaspossible.Whilea4-strokewithbadsealsandpoorlymatedcrankcasesurfaceswillleakoilandrattle(thoughruninsomefashion),its2-strokesiblinginsuchaconditionprobablywon’tevendomorethanutterafewpopswhilethestarter

ropeisyanked.Whenhealthy,theaverage2-strokewillstartquicker(becauseitrequiresonly

onerevolutionofthecrankshafttogeneratepower)andyieldhighercrankshaftrevolutions-per-minute,thoughlowertorque,thana4-strokewill.

FUEL/OILMIXTURES

Two-strokeenginesmadeafterthe1970stypicallywearfuelcapsnotingthatagas/oilmixisrequired.Older2-cyclemotorsmightnotsosignify,but,ifyourenginehasnowheretoputoilinitscrankcase(notcountingbarandchainoilreservoirsinchainsaws),it’smostprobablya2-strokemodelandwillrequireoiltobemixedwiththegasolineforproperlubrication.

Two-strokeoiladditivesaresoldinbothsmallcontainersthatarepremeasuredfor1gallonofgas,andinlargerbottlesthatoftenhaveameasuringcupattheirtopforcorrectlydispensingtheexactamountofneededoilintothegasoline.Ratiosvarydependingontheequipmentandmanufacturer.Themostcommonratiois50:1,meaningthatforevery50partsofgasoline,onepartof2-strokeoilneedstobeadded.However,othermixturessuchas32:1alsoexist,sobesuretoconsultyourimplement’sowner’smanualtoverifythemixtureyou’llneed.Ifindoubtandinapinch,usethelong-heldstandardof1/2pintoiltoagallonofgasoline(or16:1gas-to-oilratio)togetyouthroughinanemergency,asitwillnotharmyourengine.

CLEANINGA2-STROKEENGINE’SPORTS

Anyonewhohasexperiencedamiserableheadcoldknowshowdebilitatingitfeelstobeallstuffedup.Ifyour2-strokesmallenginecouldtalk,afterseveralyearsofuseit’dprobablyblamesymptomsofsluggishnessandweaknessonplugged-upexhaustports.Carbon—especiallyfromcaked,unburnedoildeposits—likestoclogexhaustportsandroba2-cyclemillofitsspunkypowerandjackrabbitacceleration.Plus,excessiveback-pressurefromsuchclogsmakeamotorhardtostart.Whilethere’snocureforthecommoncold,thegoodnewsis…a2-strokecanberemediedofitsstuffyexhaustportswithlittlemorethanasharpenedstickandafewburstsofair.

Typically,accesstotheseports(oftenintheformofonetothreeholesdrilledintothecylinder)canbegainedbyremovingthemuffler.Beingcarefulnottoletanythingfallintotheports,unbolt/unscrewthemufflerassemblyandseparateitfromthecylinder.Doingsoshouldprovideyouwithagoodviewoftheportsandtheircondition.It’snotuncommonforaportinanenginethathasbeenaroundafewseasonstobeone-thirdtoone-halfobstructedbysolidcarbon.

Amostimportantnextstepistoobserve,viawhateverviewyoumighthavethroughtheports,thepistonanditsrings.Oncespotted,thepistonneedstobeinsuchapositionastopreventjunkfromgettingintothecylinderorcrankcase.Veryslowlypullonthestartercordor(ifthatassemblyhasbeentakenoff)rotatetheflywheelmanually.Dothisuntiltheskirtornear-bottomwallofthepistoniscoveringtheports.Atthispoint,youprobablywon’tseethepistonrings,asthey’llbebeyondtheportsandtowardsthetopofthecylinder.Then,withasharpeneddowelslightlysmallerthantheport(s),scrapeawaythecarbon.Ifthestuffisreallystubborn,aplasticscrapercanbeused.Screwdriversorpunches,gentlyguided,willwork,too,butdelicatelysothatthepistondoesn’tsustainanyscratchthatcouldcompromiseenginecompression.Whenthesolidcarbonhasbeenbrokenup,blowouttheparticles,ideally,withcompressedair,beingcautiousnottogetanyofitinyoureyes.

Nowinspectthemuffler.Inolderenginesthatwerebuiltduringthedo-it-yourselfera,theseunitswereessentiallyhollowboxesandtypicallyabletobedisassembledforcleaning.It’sprobablethatyoursisfilledwithsounddeadening/sparkarrestinginnardsandhas“nouserserviceableparts;”aeuphemismfor:Youneedtobuyanewone.Dosoifyourmufflerlookscloggedandratty.Otherwise,giveitagoodsoakinginsolvent,lightlyknockitwithsomethingthatmighthelploosenthecrud,letitthoroughlydry,andreattachittothecylinderthatnowhasnicecleanexhaustports.Itisn’tunusualtofire-upyour“freshlyserviced”2-strokeandhearitspeedilythankyouformakingitfeelyoungagain.

Cleanthedebrisandbitsofoldgasketbeforeinstallingareplacement—takecarenottoletanythingfallintotheopening.

You’llneedtoremovethecarburetortogetatthereedvalveforinspectionandreplacement(ifnecessary).

CHECKINGTHEREEDVALVEINA2-STROKEENGINE

Petslovethefreedomofthoselittlespring-loadeddoorsinstalledinthebaseofaconventionalonethatallowsthemtosimplypusheitherinoroutofthehouseatwill.Forsmall2-strokeengines,however,suchlibertyaftofthecarburetorwouldletreadyfuel/airmixheadedforcombustiondecidetomakeahastyescapeoutofthefrontofthecrankcase.Onsomelarger2-cycleengines,it’sthejobofawafer-thingatekeepercalledareedvalvetokeepthefuelmixonitsproperpathwayandpreventanylossincrankcasepressure,vitalinthefuelinductionandcompressionprocess.

Widelyintroducedinthemid-1930sonEvinrudeoutboardmotors,reedvalvesarerathercarefreeunlesssomethingsuchascorrosionoraninadvertentpokewithascrewdriverbendsorbreaksthem.Notoftenfoundonnewersmallenginesthatpowerstringtrimmersorchainsaws,theyareoccasionallyfoundonolderorlarger2-strokeoutdoorpowerequipmentengines.Exactplacementvariesfromenginetoengine,butreedvalvesareusuallyeitheraffixedtoaplatedirectlytotheoutsideofthecrankcase(inbackofthecarburetormountingflange),aspartofaremovablereedplateassembly“block”thatfitsintothefrontofthecrankcase,orscrewedtoareedplateattachedtotheinsidefrontofthecrankcase.

Often,reedshavearoughedgeandasmoothedge,withthelatterinstalledtowardsthereedplate.Carburetorcleanersolventmaybeusedtocleanthereedsandrelatedareas.Treatthereedsasdelicateinstrumentsbeingcarefulnottobendthem.Afeelergauge(liketheoneforcheckingsparkplugelectrodegaps)shouldbeusedtomeasureclearancebetweenthereedanditsplate.Whilespecificationsdiffer,many2-strokeenginesworkbestwithareedclearanceofnomorethan.015inch.Ratherthanattemptingto“re-bend”reedsthatareoutoftolerance,newonesshouldbeinstalled.

CHAINSAWMAINTENANCE

It’sagoodbetthatachainsawthateitherwon’tstartorfinallydoes,butrunsandcutspoorlyisavictimofcaked-onoilysawdustanddirt,withatleastapinchofbadfueltotopoffitstroubles.AfteranhourortwoofTLCintheformofde-gunking/cleaningtheairintakefilter,carburetor,andservicingthechain,mostoldsawswillbebuzzingawayatthewoodpile.Theprocessoftenincludesseeingifthesaw’ssparkplug/ignitionsystemyieldsspark,emptying/cleaningthefueltankandfuellinefromtankto“carb.”

Becausechainsawstypicallyemploya2-strokeengineandadiaphragmcarburetor(asopposedtoonewithagravity/fuelactivatedfloat),theycan

literallyberunupsidedown.Thisdiaphragmisapaper-thinpieceofsyntheticrubberabout2inchessquarethattendstogetbrittleorstiff(thusloosingitseffectiveness)withageorexposuretoharshconditions.“Carburetorkits,”astapleofsmall-engineshops’partsdepartmentsandsomethingveteransawshopetoeventuallyenjoy,oftencontainreplacementdiaphragmsandrelatedgaskets,seals,needlevalves,andspecificinstallationdirectionsforrenewingcarburetion.

Chainsawsrequirediligentcleaningtorunsmoothly.

BAR/CHAINOILPUMP

Thebar/chainoilsystemshouldalsobeonachainsawowner’smaintenanceroster.Itpumpslubricationfromatanktotheareawherethechainrotatesinthegrooveinthechainbar.Notethatthislubeisnotrelatedtotheoilrequiredforthe2-strokeengine’sgas/oilfuelmix.Likeanyothermachinery,thisbar/chainoilingsystemneedstobefreeofdirtanddebriswantingtoblockorreduceoilflow.Ofcourse,themoreoilsquirtedontothebarandchain,themoresawdust

anddebriswillsticktothem.That’swhykeepingthesawcleanissocritical.Somepumpsworkautomaticallyoffacaminthecrankshaft,whileotherssimplyutilizeaplungerpumpabitliketheonesthatdispensehandsoapinafancybathroom.Theolder,manualtypeissometimesfittedwithableederscrewthatallowsadjustmentforimprovedhydraulics.There’slikelytobeanairscrewonautomaticoilers,too.Nomatterthestyle,though,thepumpoutputisinthevicinityofthebarmountingboltsandcentrifugalclutchthatdrivesthechain.Thatmeansaccessforcleaningrequiresremovalofthedriveclutch,ataskthatmightpresentabitofaconundrumbecauseturningit(typicallyscrewedontothecrankshaftviaaleft-handthread)rotatesthecrankshaftalongwiththerestoftheengine’smainparts.

Removingtherewindstartertobeabletogetaholdoftheflywheelwillbenecessarytokeepthecrankshaftstillsothattheclutchassemblymayberemoved.

Beforeproceeding,besurethatthegrooveonthecircumferenceofthebar(inwhichthechainguidesride)isfreeofobstructions.Runthetipofacleanstandardslotscrewdriverinthegrooveandaroundthebartocheckforblockageand/or“pinches”inthisgroovethatwouldimpedeoilflowandincreasechainfriction.Cleanandstraightenaccordingly.Lookfor/cleananypassagesrunningfromthegrooveintothebar.Next,unscrewthepumpassembly(oftenplastic)andgentlypryitloose(alongwiththerelatedoilline)fromthesawwithaflatscrewdriver.Givetheunitathoroughcleaning,thenreversetheprocesstoreinstallthepump.

BAR/CHAIN-GUIDES

Thoughabarcanbecomedistortedfromitssawbeingdroppedorwedgedintowhateverit’scutting,thechainismoreoftentheculpritwhentheoldexpression,likeahotknifethroughbutter,isnotfitting.Thebestwaytoinspectfor“barbend”islikeonewoulddoinordertodetermineifa2×4pieceoflumberisstraight;lookatitacrossthetopfromenginetotip.Whileexperiencedmachinistscouldprobablyperfectlystraightenabentbar,itisrecommendedthatabarwithanytwistsorcracked,broken,orsquishedchainguidegroovesneedsreplacing.Thesamesuggestionappliestoabarwithatipgearthatnolongerspinsfreely.Ifthechainbarfitsbothways,evenwiththemanufacturer’slogoreadingupsidedown,itmaybe“flipped”sothatthedownside(wheremuchofthechainpressureisexertedduringcutting)canserveatthetop,thusevenlysharingthewearovertime.

CHAIN

Beawareofchaintensiononyoursaw.Consulttheowner’smanualforpropertensionspecifications.Notethatachainrunningtoolooselyonitsbar/chainguideswillreallywearintothebar,especiallyattheheelandjustunderthenose.Thechaincanbetightenedbylooseningthetwonutsonthebarbolts(stickingthroughtheenginecrankcase),adjustingthebarforward,andretighteningthenuts.

A5/32roundfile,aflatfile,andguidegaugeareessentialswhensharpeningyoursaw’schainblade.Mountingthesaw(viaitsbar)inasturdyviseisonewaytohavegoodaccessfortheprocedure,thoughsharpeningtheunitwhileit’sonaworkbenchorthegroundiscommonplace.Inanyposition,however,besurethechaincanrotatefreely.Thataccomplished,placethechainguideoverthechaintogaugethedesiredangle(typically30or35degrees),removeitandusetheroundfiletotreatthefront/cuttingedge“tooth”ofthechainatthedeterminedangle.Rememberthatthesharpeningactionofthefileshouldbeinthe“push”direction,notthe“pull.”Keepthatfilelevel,too.Usethegaugeaftertreatingeachbladetoothtotestwhetherithasbeenfiledtotheneededangle.Somechainsawfilesarefittedwiththeangleguidesforeaseofoperation.Feelfreetodrawacoloredmarkerlineoneachnownewly-shinytooththatyou’vefiledsoyoucanseewhat’sbeencompleted.Routinely,cleanoffthefilesoitdoesn’tfillwithmetalparticlesandoil.Thatflatfilecanbeusedtofiledownanychainguidethatprotrudesbeyondtheguidegauge.Tofileteethrunningoppositeoftheonesyoujustsharpened,turnthesawaround180degrees.Nomattertheside,treateverytoothwiththesamenumberoffileruns,sotheteethwon’tendupbeingvarioussizes.

Chaintensionisadjustedbylooseningthebarboltsandmovingthebarforwardorbackward.

Keepingyourchainsharprequiresaroundfilewithaguidegauge.

STRINGTRIMMERANDLEAFBLOWERMAINTENANCE

Maybeit’sbecausethoselittlegastrimmersandblowerscansometimesbeboughtnewfornotmuchmorethanthepriceofacoupleofgoodshovelsthattheydon’tgetthecaretheydeserve.Ifdoingnothingelse,atrimmerownershouldcommittokeepinghis/herunitcleanwitharag.Specialattentionshouldbedevotedtotheengineairfilter,whichevenifpartiallyblockedwithgrassclippings,dust,leaves,etc.,willcausethetrimmer’s(typically)2-strokeenginetorunpoorly—ifitevenstartsatall.Anenginethatsoundslikeit’srunningslowerthannormalandlackspowercouldbesufferingfromairintakeobstruction.Foamfilterscanbewashedingrease-cuttingsoapywater,butneedtobecompletelydrybeforere-fittingtothecarburetor.Theexhaust/mufflershouldbefreeofobstructions,too.

Ifyou’venotrunthetrimmerinawhile,checkthefuelcolor.Particularly

darkfuel—asopposedtoafreshtranslucentmixofgasolineand2-stokeoil—isabadsignandshouldbedrainedbeforeacleanfillisfacilitated.Goodfuelflowisessentialonatrimmer.Ifyouseeairbubblesinthefuelline,itcouldhavewaterinitorthelinecouldbecrackedandallowingair.Whiteorgrayish-whiteexhaustsmokeisatelltaleofwaterorsomekindofdebrisinthefuel/line.

Atseason’send,drainthefuelfromthetankandthenruntheengineuntilthecarburetorisempty.Introduceafewsquirtsofoilintothesparkplugholeandpullthestarteracoupleoftimestonicelydistributethelubeonthosemovingpartsabouttotakealongwinter’snap.

Andnowawordabouttheotherendofatrimmer:Thepartthatisaskedtodothedirtywork.Checkthecuttingstring(orbladesystem)andreplacethestringspoolbeforeithasachancetorunoutorbreakapartonthejob.Manystringheadscanberemovedfromtheirtrimmersbypushinginwardandturningtheunitcounterclockwiseuntilitcanbeclicked/pulledoff.Thosewithoutthepatiencetodothingslikethreadasewingneedleoruntanglefishinglineunderstandablyavoidwindingbareplasticcuttingstringthroughtrimmerheadguides.Theyshouldn’tfeelbadaboutspendingafewextradollarsonacompletereplacementstringcartridge(lookforaheaviergradeofline,ifavailableforyourmodel)thatcanbepoppedintoplace,aslongasthetrimmerheadhasbeenkeptreasonablycleanandtidy.

Atseason’send,alwaysdrainthegasfromyourstringtrimmersoyoucanstartfreshnextyear.

Indexaircleaners,46,54–56alternators,testing,115

batteries,10,27,115bolts,tightening,59brakebands,servicing,136–137brakepadsremoving,133testing/inspectingsystems,134

brakingsystemcomponentsof,26reassemblyof,135servicing,132Seealsobrakebands;brakepads

carbondeposits,118–121carburetorsabout,10–11,17–19,101adjustingchokelinkage,83adjustinghigh-speedmixture,83adjustingidlespeed/mix,82altitudecompensation,106commonproblems,38disassembling,103–105findingfuelsupplyproblems,81inspectingmixturescrews,106overhauling,100reassembling,107removing,102servicing,80

chainsaws,141–142

choke,adjustinglinkage,83combustionchamber,sealing,47commonproblemsdiagnosing,36–37knocking,41non-rotatingengine/flywheel,38non-startingengine,38–39overheating,40smoking,40sparkplugs,41

compressionsystemcommonproblems,12,39componentsof,8,12–13,16testingenginecompression,58Seealsopistons;valves

coolingsystem,9,24crankcasebreathers,59cylinders,removingcarbondeposits,118–121cylinderheads,reassembling,121

debris,removing,69–71diagnosingproblems,36-37.Seealsocommonproblemselectricalsystemcomponentsof,27,118testing,114–116Seealsoalternator;battery;externalstators

enginecompression,testing,58enginedegreasing,72exhaustvalves,10.Seealsovalvesexternalstators,116–118

flywheelkeys,inspecting,109flywheelsabout,11,19–21inspecting,108–109installing,109removing,109

4-strokeengines,described,7–11fuelcaps,sealing,45fuelfilters,inspecting,76fuellines,17–18,38fuelpumps,servicing,78–79fuelsystemcomponentsof,11,17–18,38findingfuelsupplyproblems,81Seealsocarburetors;choke;fuelcaps;fuelfilters;fuelpumpsfueltanks,33,

74

gasoline,32,77,138governorsystemadjustinggovernedidle,88adjustingstaticsetting,87adjustmentmethods,88componentsof,10,25,84–85huntingandsurging,86inspecting,86linkages,25partsofmechanical,85settingtopno-loadspeed,89

ignitionarmatures,20–21,110–113ignitionsystemcommonproblemsand,39componentsof,9–10,20–21solid-state,20Seealsoflywheel;ignitionarmatures;sparkplugs

intakevalves,10.Seealsovalveslawnmowers,60–61,98–99lawntractors,,62–63leafblowers,143L-headvalves,12.Seealsovalveslubricationabout,9–10,22–23oncables/linkages,59ofinternalparts,46

maintenanceend-of-season,45–47oflawnmowers/lawntractors,60–63ofleafblowers,143ofpoweraugers,62schedulefor,44ofsnowblowers,64–65ofstringtrimmers,143

mechanicalgovernors,25,85,87mixturescrews,inspecting,106mufflers,inspecting/replacing,92–95

oilabout,22–23changing,44,45,51changingon4-stroke,48,50checkingon4-stroke,492-strokeenginesand,138

oilfilter,23overheadvalves(OHV)about,12,16adjusting,131installing,130–131removing,129

pistons,removingcarbondeposits,118–121pneumaticgovernors,25poweraugers,62

regulator,27repairs,generalinformation,68rewindcords,10–11rewindstartingsystem,90–91

safetyprecautions,32–33,76,91,115,135snowblowers,64–65sparkplugs

about,10–11,20–21checkingforsparkmissand,53checkingignitionofwithsparktester,53cleaning/inspecting,52–53commonproblems,41inspectionof,46servicing,52

stabilizer,adding,45stopswitches,testing,111stopswitchwires,checking,72stringtrimmers,143

tools,28–312-strokeenginesabout,7,138cleaningportsof,139componentfunctions,10fuel/oilmixtureand,138reedvalves,140

valvesaccessing,124adjustingtappetclearances,127designof,123inspecting,126installing,128lapping,127machining,124removing,125servicing,122valvelife,127

valvespringcompressors,124

Firstpublishedin2014byCoolSpringsPress,amemberoftheQuaysidePublishingGroup,400FirstAvenueNorth,Suite400,Minneapolis,MN55401

©2014CoolSpringsPressAllrightsreserved.Withtheexceptionofquotingbriefpassagesforthepurposesofreview,nopartofthispublicationmaybereproducedwithoutpriorwrittenpermissionfromthePublisher.

Theinformationinthisbookistrueandcompletetothebestofourknowledge.AllrecommendationsaremadewithoutanyguaranteeonthepartoftheauthororPublisher,whoalsodisclaimsanyliabilityincurredinconnectionwiththeuseofthisdataorspecificdetails.

CoolSpringsPresstitlesarealsoavailableatdiscountsinbulkquantityforindustrialorsales-promotionaluse.FordetailswritetoSpecialSalesManageratCoolSpringsPress,400FirstAvenueNorth,Suite400,Minneapolis,MN55401USA.Tofindoutmoreaboutourbooks,visitusonlineatwww.coolspringspress.com.

Digitaledition:978-1-62788140-1Softcoveredition:978-1-59186-587-2

LibraryofCongressCataloging-in-PublicationDataSmallenginesandoutdoorpowerequipment:acare&repairguideforlawnmowers,snowblowers&smallgas-poweredimplements/editorsofCoolSpringsPress.

pagescmISBN978-1-59186-587-2(pbk)1.Smallgasolineengines--Maintenanceandrepair.2.Gardening--Equipmentandsupplies--Maintenanceandrepair.I.CoolSpringsPress.II.Title:Smallenginesandoutdoorpowerequipment.

TJ790.S58272013621.43’40288--dc23

2013028515

AcquisitionsEditor:MarkJohanson

DesignManager:BradSpringerLayout:LaurieYoungCoverDesign:SimonLarkin10987654321