# Starter motor operating principles

When the ignition switch is turned to energize the solenoid, its armature pushes the pinion towards the flywheel ring gear with the engagement lever.

As the pinion is pushed forward it is forced to rotate by the spiral splines on the pinion shaft. Shortly before the end of the solenoid armature travel is reached, the solenoid switch completes the main current circuit and the armature begins to rotate.

As a result of the spiral action of the splines, the pinion continues to move towards the flywheel ring gear until it reaches its travel limit on the pinion shaft and begins to turn the engine over.

To prevent the starter from being driven at an excessive speed because of the high reduction ration between starter pinion and flywheel ring gear, an over run device is incorporated in the pinion assembly.

As soon as the starter is switched off, by releasing the ignition key, the pinion returns to its rest position.

To ensure that the starter comes to a halt as soon as possible after being switched off, it incorporates and armature brake.

E30 M3 Repair Manual V2.7. Copyright ©1999-2001 Koala Motorsport & Brett Anderson