aircooled engine technology - grafton school district...12. the shape of the piston head has a lot...

AirCooled Engine Technology

Roth 9 th Ch 16 Pistons & Piston Rings Pages 287 301


Rings Skirts Things

1. When reconditioning engines, ___________ and ___________ _________ are critical service items.

AirCooled Engine Technology 2. The need for piston and piston ring service is evidenced by low __________,

blowby, oil pumping up into the combustion chamber, blue exhaust smoke and ____________ spark plugs.

Compression, Fouled Resale Value, Broken Combustion, Failed


Breather orOil Fill Tube

Wet Test that is 20% Higher than the Dry Test Indicates Piston Ring or Cylinder Crosshatch Wear


Breather orOil Fill Tube

Cylinder leakage heard at the oil fill tube is evidence of piston ring or cylinder

cross hatch wear.


• Reads in inches of water. • Reads vacuum 40 inches of water. • Reads pressure 40 inches of water. • Vacuum is displayed as negative and Pressure is displayed as positive. • Has a 3.5 digit display with a 1 15/16 " X ¾ " view area. • Powered by a 9 volt battery and indicates LOW BAT when it needs to be replaced. • Include is a clear vinyl tube 24" long and can be replaced. • Has 274 graduations in one PSI of pressure. • Comes with a blue vinyl protective cover that can be removed to replace the battery

AirCooled Engine Technology 3. Pistons are usually made of lightweight __________________ and are

chrome alloy plated so that when they are used in aluminum bores, the metals are dissimilar. This limits metal transfer problems.

Cast Iron Aluminum Plastic

AirCooled Engine Technology 4. The areas between the ring grooves on the piston are called the ring ______.

Wear on ring lands is determined by measuring ring groove side clearance using a new piston ring & flat feeler gage.

Lands Slats Areas

AirCooled Engine Technology 5. The piston _____________ is the area below the bottom ring groove. The

length of the skirt helps the piston to resist tipping from side to side as it reciprocates in the cylinder. Tipping = slapping sound.

Shirt Skirt Squirt

AirCooled Engine Technology 6. In 3rd port or piston port valving design 2 cycle engines, the piston _______

may be cut away to allow the air/fuel/oil mixture to pass from the carburetor into the crankcase.

Wort Skirt Head

AirCooled Engine Technology 2 stroke cycle engines may also use ________ valves

or may use rotary valves to open & close ports.

AirCooled Engine Technology 7. The piston is made .003”.005” smaller than the bore diameter to allow for

thermal _____________ which happens as it heats up during operation. A cold piston is smaller in diameter and may slap more.

Contraction Expansion Retraction

AirCooled Engine Technology 8. A _______________________ piston is cast & machined round and then

ground to an oval shape. It is smaller in diameter across the nonthrust surfaces which are parallel to the crankshaft & wrist pin.

CamGround CanAm OvalShaped

AirCooled Engine Technology 9. As a camground piston heats up during operation, it gets _____________

instead of oval shaped, providing a close fit in the bore once the engine is warmed up. This controls piston thermal expansion.

Square Round Thinner

AirCooled Engine Technology 10. Piston _______ is the action of the loosefitting thrust surfaces hitting the

cylinder wall so hard on the compression and power strokes that the noise can be heard above the normal exhaust noise.

http://www.mce5.com/mce5_technology/images/reliability/radial_mot_mce5.gif

Slap Strap Scrap

AirCooled Engine Technology 11. The _______ of the piston runs hotter than the skirt and will expand more

during operation. To compensate for this expansion, the piston crown is made smaller in diameter than the piston skirt.

Head Skirt Pants

AirCooled Engine Technology 12. The shape of the piston head has a lot to do with ________________ the

spent air/fuel mixture out of the cylinder. Piston heads can be flat, domed (loop), wedged, recessed, or contoured (cross).

Scavenging Harpooning Trashing

AirCooled Engine Technology 13. Piston ____________ do the job of sealing combustion gases into the

combustion chamber. During operation they ride on a thin film of oil which is held in the cylinder crosshatch surface pattern.

Rings Skirts Things

AirCooled Engine Technology 14. Piston rings can be made of _________ _________ or steel.

They have coatings to increase durability.

Cast Iron Cast Aluminum Cast Magnesium

AirCooled Engine Technology 15. _______________________ the top 2 rings on the piston designed to

seal compression.

Compression Scraper Oil Control

AirCooled Engine Technology 16. The _____ ____________ ring is designed to remove the surplus oil from

the cylinder wall by passing it through holes in the ring & the piston. The oil may then be used to lubricate the wrist pin.

Compression Scraper Oil Control

AirCooled Engine Technology 17. Ring ______________ causes the ring to exert force on the cylinder wall

even with the engine at rest.

Tension Voltage Slapping

AirCooled Engine Technology 18. Most 4 cycle engines have __________ rings, which rotate in the grooves

as the engine runs.

Pinned Floating Welded

AirCooled Engine Technology 19. Many 2 cycle engines h____________ rings, which are held from floating.

This prevents the ends of the rings from getting caught in transfer & exhaust ports and breaking off.

Pinned Floating Welded

AirCooled Engine Technology 20. Piston rings must have _______ ______________ in the grooves to allow

for floating, heat expansion, and adequate lubrication. (measured with a new ring & a flat feeler gauge)

End Gap Side Clearance Radial Runout

AirCooled Engine Technology 21. As a rule of thumb, allow a minimum of _______ “ ring end gap for

every inch of cylinder diameter.

.003” .004”

.012” .020”

.0005” – .0010”

“Bench Marks”

.002” = one hair

.004” = thickness of paper

.040” = thickness of a dime 1mm = .040” = 1 dime

AirCooled Engine Technology 22. Too __________ ring end gap will cause blowby, low compression, and

blue smoke from oil pumping.

Much Little Late

AirCooled Engine Technology 23. Too _____________ ring end gap will score the cylinder walls as the rings

expand and fit too tight.

Much Little Late

AirCooled Engine Technology 24. Ring end gap is measured with a flat ____________ gage inserted between

the ends while the ring is off of the piston but has been pushed straight into the cylinder bore using the inverted piston.

Wheeler Dealer Feeler


Ring End Grinder

Offset crankshaft to control slap

AirCooled Engine Technology 25. Excessively tapered and outofround cylinders can only be repaired by

____________ (boring out) to the next .010” increment over standard size. Then they must be fit with a new O.S. piston & O.S. ring set.

Oversizing Undersizing Siezing

AirCooled Engine Technology 26. Most piston and ring damage/wear can be traced to causes such as

lack of _________________, using the wrong SAE or API grade of oil, using the wrong gas:oil mixture (2 cycle), use of an incorrect type of ______, foreign particles in the cylinder from an improperly serviced ______ filter, clogged __________ fins, excess carbon buildup in the exhaust ports, & improperly fit pistons & rings.

Lubrication, Fuel, Air, Cooling Maintenance, Plug, Fuel, Oiling Use, Fuel, Air, Flywheel

AirCooled Engine Technology 27. Worn rails on oil control rings indicate ________ have entered the engine

through a neglected, damaged, or improperly fitting air filter…or, of course, abrasives in the crankcase oil.

Water Abrasives Objectives

AirCooled Engine Technology 28. ___________ is abnormal combustion which causes too much pressure

and excessively high temperatures in the combustion chamber. This problem can produce an engine “ping” or “knock” and cause NOx too!

Detonation Preignition Dieseling

AirCooled Engine Technology 29. ______________ is the burning of the air/fuel mixture before the time that

the spark normally starts the ignition process. This problem can produce an engine “ping” or “knock” and cause NOx too!

Detonation Preignition Dieseling

AirCooled Engine Technology 30. Piston pins, often called ______ pins, are used to fasten the upper end of

the connecting rod to the piston. They may be pressfit or may be fullfloating & held in to place with snap rings or clips.

Wrist Rod Crank


Piston Ring Expander

Piston Ring Compressor

Used for removing rings from a piston Used for replacing rings on to a piston

Used to install piston & rings into a cylinder


Wrist Pin Press

Wrist Pin Press

aircooled engine technology - grafton school district...12. the shape of the piston head has a lot...

Documents