Engagement is provided by Operation of the Ignition switch in the Start position, which activates a start amounted solenoid, whose plunger is engaged with the hook-dend of opinion shift lever and operating fork. Solenoid operation moves the operating fork, causing the opinion to engage with the ring gear and also causes the plunger contacts to bridge the main start terminals. The fork locates in a guide ring on opinion driver, which is coupled to the opinion via a roller type overrunning clutch designed to transmit drive in one direction only. The opinion driver is mounted on a helix, machined on the armature shaft, to form a very coarse thread. This allows the opinion driver to rotate slightly when it has moved towards the ring gear, and this feature, together with a chaffer on the leading edge of the ring gear and opinion teeth, is designed to assist meshing and easy engagement. However, if the opinion teeth butt against the ring gear teeth an engagement is prevented, the guide ring continues its axial movement by sliding over the sleeve of the driver and compressing a meshing spring until the plunger contacts bridge the main terminals and the armature begins to turn. The armature rotation and the force from the meshing spring allows the opinion teeth to drop into mesh with the ring gear assisted by the screw action of the helix. The helix forces the opinion further into the ring gear until opinion contacts a stop ring on the armature shaft. This prevents further axial movement and the driver and opinion now locked to the shaft via the helix and overrunning clutch and transfer the armature rotation to the flywheel. The opinion has only a small number of teeth compared to the ring gear and this means the armature will rotate several times for each revolution of the flywheel. The gear reduction also multiplies the torque from the starter motor. As soon as the engine starts, its rotational speed will eventually exceed the speed of the armature. At this instant, the overrunning clutch breaks the connection between the opinion and the armature shaft and prevents over-speeding and damage of the armature. The opinion remains meshed as long as the engaging lever is held in the engaged position. Releasing the starter switch allows the solenoid plunger return spring to return the engaging lever, driver and opinion to their original position.