oscillating magnetos jack beater 1940

Upload: steven-howell

Post on 06-Apr-2018

224 views

Category:

Documents


0 download

TRANSCRIPT

  • 8/3/2019 Oscillating Magnetos Jack Beater 1940

    1/3

    ONE of the most popular types of oscil-lating magnetos, which is used exten-sively on small one-cylinder gas enginesSupplying power for boats, lighting plants,light machinery and pumps, cannot betested on any ordinary type of generatoror magneto test bench as the magnetohas no rotating parts. The crossbar or"armature" of this magneto is "kicked" upand down on the pole ends to make andbreak the magnetic field, and to open andclose the primary circuit. It is a simplehigh-tension magneto, consisting mainlyof two laminated pole pieces, eight plain-bar magnets, two coils containing both theprimary and sec-ondary windings,points, condenser,and laminated ar-mature. The oper-ating principle iseasily understood.The bar magnets,clamped between

    the pole pieces, sup-ply the initial en-ergy and make onepole piece a northpole and the other asouthpole. The coilsare hollow and slipover the pole pieces.The laminatedcrossbar, or arma-ture, rests upon thetops of the polepieces and providesa path for the mag-netism to travelfrom the north to the south pole.

    When the engine mechanismmoves the crossbar from the topsof the pole pieces, the flow of mag-netism is interrupted. This actioncreates an electrical current thatflows through the primary wind-ings of the two coils. An instantafter the crossbar has left the poletops the continued movement ofthe crossbar opens the points, andthe current flow in the primary issuddenly interrupted. This inter-

  • 8/3/2019 Oscillating Magnetos Jack Beater 1940

    2/3

    coils is made by a short coil spring in-sulated with varnished tubing. The ter-minal button on one coil is alwaysgrounded to the outer cover, while theother button connects through a smallcoil spring to the high-tension terminalof the magneto. The pathsof the primary and second-ary circuits are shown inthe circuit diagram, Fig. 3.The coils can be tested onone of the standard mag-neto coil testers such as

    that shown in Fig. 4.The construction of a teststand for this magneto isshown in detail, in Figs. 5and 6. The channel-steelupright is welded to thesteel base plate. Above thisa small steel block is weld-ed to the upright to holdthe magneto in the rightposition for testing with thecrossbar down, Fig. 1. Im-mediately above the mag-neto, the trip-shaft guideblock is welded to theframe. The guide block isruption induces a high-voltage current in assembled from ordinary square and flatthe secondary windings of the coils that steel stock and spot welded together. Nearpasses out of the m agneto terminal and to the top of the upright a 3-in. length of 2-in.the spark plug. The engine mechanism pipe is welded through and at right anglethen returns the crossbar to its original to the frame. Before welding into place,position on the ends of the pole pieces, this pipe is machined inside to take the

    completing the cycle.wo ball bearings used to support the fly-The coils of this magneto are quite wheel shaft. The flywheel can be of castrugged but occasionally become defective iron or steel and is a press fit on the shaft.due to excessive m oisture or other causes. A floating boss is mounted in a drilled holeThe high-tension terminal of each coil near the rim of the wheel and controls theconsists of a small brass button, and the action of the spring-loaded connecting rod.high-tension connection between the twohe latter is made of 3 /8-in. cold-rolled

  • 8/3/2019 Oscillating Magnetos Jack Beater 1940

    3/3

    steel rod, threaded at one end and heatedand flattened at the other. A turned collarat the bearing end supports the bottomloading spring, while the tension of the toploading spring is adjusted by means of anut and lock nu t. The loading springs areof the coiled-wire type.The trip shaft is easily made from 3 /4-in.square steel bar. It must be notched atboth ends as show n and m ust slide freelyin the guide. A crank handle can be pro-vided on the flywheel shaft for manual op-eration, or a pulley for motor drive.Now, in operation the floating boss com-presses the top spring as it moves upward.Slightly before top dead center the coilspring is fully loaded and the continuedmovement of the boss "bumps" the con-necting rod upward. The latter being en-gaged w ith the lifter pin of the crossbar onthe magneto, snaps the armature from thepole tips and pulls it upward as the springunloads tension. The bump of the flywheelboss on the fully compressed loading springcauses the initial separation of the arma-ture from the pole tips but the balance ofthe snappy upward movem ent of the arma-ture is caused by the unloading of the topcoil spring. On the downward half of thecycle the flywheel boss loads the lowercoil spring and re-engages the armaturewith the pole tips. Unless the armaturemakes a good contact with the pole tipsafter each spark the magneto will miss onthe next revolution. Hence the lower load-ing spring is important but not critical inadjustment.A small Bakelite panel is mounted abovethe magneto on the front of the trip-shaftguide housing, Figs. 2 and 5. T he panel isfitted with an adjustable spark gap forchecking the condition of the spark. Ahigh-tension cable and clip are permanent-ly attached to the panel for connection tothe magneto high-tension terminal.When operated by hand the magnetocan be tested at any speed, from one revo-lution per minute up to several hundred ormore. Because it duplicates the trippingaction as found on all engines using thistype of magneto, the tester can be depend-ed upon to prove the condition of the mag-neto before it is put back into service. Thetester shown here was designed and builtin a magneto repair shop, where it hasgiven splendid results.