Three starter motors are used on these engines. The SD-260 is a straight drive starter with the pinion driven directly by the armature shaft. Pole pieces are arranged around the armature that is energized by wound field coils (figure 3). This type is used on gas engines.

The PG-260 achieves gear reduction at a ratio of 5:1 through planetary gears. Its relatively small size and light weight offers improved cranking performance and reduced current requirements for larger gasoline engines (figures 4 and 5).

The 28-MT, used on diesel engines, is a gear reduc­tion starter with an over running roller type clutch and an enclosed shift lever (figures 6 and 7).

Enclosed shift lever cranking motors have the shift lever mechanism and the solenoid plunger enclosed in the drive housing, protecting them from exposure to dirt, icing conditions, and splash.

Solenoid windings are energized when the ignition switch is in the start position. The resulting plunger and shift lever movement causes the pinion to engage the engine flywheel ring gear, the solenoid main contacts to close, and cranking takes place. When the engine starts, the pinion overruning clutch protects the arma­ture from excessive speed until the ignition switch is released, at which time the plunger return spring causes the pinion to disengage. To prevent excessive overruning, release the switch from the crank position as soon as the engine starts.

For bench repair of the SD-260, or 28-MT starter motors, refer to the Light Duty Truck Unit Repair Manual. PG-260 model starters are serviced by replacement only.


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