Starter Motor Driving Mechanism

Starter motor drive mechanism

The ratio between the starting motor pinion gear and the ring gear in engine flywheel is varied from 1:10 to 1:15. For example, if the ratio 1:15 means, the flywheel will rotate 1 revolution when the motor pinion rotates 15 revolutions. Once, the engine is cranked, then the speed of the engine will increase. If the starter motor is continuously engaged, then the enginenwill drive the motor and the speed of the motor will be 15 times higher than then engine speed. This will lead to failure of the starting motor. To prevent this, pinion
gear should be disengaged from the flywheel ring gear once the engine is started and the mechanism used for disengagement is called as starter motor drive mechanism.

Types of starter motor drive mechanism

1. Bendix drive
2. Over running clutch type
3. Folo – thru system
4. Rubber compression system
5. Sliding armature system
6. Parallel type system
7. Friction clutch system

Bendix drive starting system


There is a threaded sleeve in an
armature shaft. The sleeve will move on the shaft back and forth. Armature shaft is directly connected to the drivehead. Coil spring is mounted over the sleeve. Pinion will be over the sleeve. There is an unbalanced weight on the pinion.


When the starter switch is “ON”, armature and sleeve assembly rotate. While rotating, the pinion moves over the sleeve due to inertia as pinion is loosely mounted over the sleeve. The pinion is engaged with the flywheel ring wear and start the engine. As the engine speed increases, the pinion retracts and go away from the engine flywheel.

Starting switch

The switch is a device which is used
to open and close the electric circuit. A starting switch is used between the starter motor and the battery. In this, plunger,contact disc, pull-in windings, terminals and connection wires are there. When the switch is on, the current passes from the battery to the pull-in – windings and it get magnetised. It pulls the contact disc and closes the circuit between the battery and the starter motor. When the switch is off, the pull-in – windings get demagnetise and the spring makes the circuit open between the battery and the starter motor.nIt is also called as ‘Solenoid Switch’.

Maintenance of starter motor

1. Starting motor should not be operated continuously for more than 30 seconds.
2. Once the engine is turned on, the
startingswitch should be released.
3. Periodic greasing should be made.
4. Ensure the proper tightness of cable
5. Replace the faulty bearing immediately
6. Don’t crank the engine frequently, if the engine fails to start

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