Starter drive in an electric motor initiates rotational motion in an internal combustion engine before it can power itself. It is used to connect and disconnect rotating starter motor shaft to the engine for cranking. The drive comprises of small steel or nylon pinion gear that connects to the end of the starter armature shaft. Inertia starter drive is used to engage and disengage the starter pinion from flywheel ring gear.
The starter drive can be used for both gas turbine engine and diesel engine, particularly trucks, use a pneumatic self-starter.
When operator turns the key, the pinion gear of the starter drive meshes with the ring gear of the engine's flywheel. The current passed through passed through battery drive the pinion initiating the movement of flywheels and cranks. There is a gear reduction between pinion and flywheel ring gear resulting in increase of starter motor torque. This allows the small electric motor to crank the gasoline engine. There are almost 15- 20 teeth on ring gear. This means that armature will rotate 15 -20 times on a single rotation of the ring gear.
The pinion gear cannot remain meshes once the engine starts. Because this engagement may cause the ring gears to rotate at a very speed, due to the reduction. Hence, the key-operated switch is opened, a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops. Pinion is clutched to its driveshaft through an overrunning sprag clutch that permits the pinion to transmit drive in the single direction.
Starter assembly do not last to the life of starter motor. The starter drive should be replaced by the technician over a period of time. Noise that can be heard coming from the starter is usually produced from the drive. The starter wines or grinds and does not turn engine over reliably.
Sometimes, the overrunning clutch will slip in one direction when it wears internally. Test it by trying to turn the drive in both the directions. Sometimes, it is necessary to wiggle the gear and attempt to turn it slightly to get it slip.
Generally in the motor starter, the drive unit is held in the place on the armature shaft by split metal ring, covered with full round ring.
- Tap down the outer ring to remove it from covering the inner ring.
- Remove snap ring.
- Slide the starter drive from amateur.
- Before replacing the starter drive from new one count the number of teeth from drive pinion and match up the new drive with the old one to check they are same.
- When replacing starter drive be sure to inspect the starter gear for damage, specially if the starter drive pinion shows any sign of wear or damage
- To reinstall the snap ring, use hammer and block of wood or rubber mallet.
- Use two pairs of plier to compress the ring assembly together.