 The pinion incorporates a one way clutch so that when the engine starts and runs it will not attempt to drive the starter motor at excessive RPM.Some older starter designs, such as the Bendix drive, used the rotational inertia of the pinion to force it along a helical groove cut into the starter drive-shaft, and thus no mechanical linkage with the solenoid was required.If a starter solenoid receives insufficient power from the battery, it will fail to start the motor, and may produce a rapid clicking sound.