The SD-255 starter motors have pole pieces that are arranged around the armature. Wound field coils energize the pole pieces. The solenoid windings are energized when the ignition switch is turned to START. The resulting plunger and shift lever movement causes the pinion to engage the flywheel ring gear and the solenoid main contact switch to close. When the engine starts, pinion overrun protects the armature from excessive speed until the switch is opened. Once the solenoid windings are deenergized, the return springs causes the pinion to disengage. The switch opens immediately when the engine starts in order to prevent excessive overrun.