SPROCKET 8W8287 - Caterpillar

Illustration 1 g00285113
Cross section of the starting motor (typical example)
(1) Field winding
(2) Solenoid
(3) Clutch
(4) Pinion
(5) Commutator
(6) Brush assembly
(7) Armature The starting motor has a solenoid (2). When the start switch is activated, electricity will flow through the windings of the solenoid. The solenoid core will move in order to push pinion (4) with a mechanical linkage. This will engage with the ring gear on the flywheel of the engine. Pinion (4) will engage with the ring gear before the electric contacts in solenoid (2) close the circuit between the battery and the starting motor. When the circuit between the battery and the starting motor is complete, pinion (4) will turn the engine flywheel. A clutch gives protection to the starting motor. The engine can not turn the starting motor too fast. When the start switch is released, pinion (4) will move away from the flywheel ring gear.Starting Motor Protection
The starting motor is protected from damage in two ways:
The starting motor is protected from engagement with the engine when the engine is running. The control feature will not allow the starting motor to engage if the speed is above 0 rpm.
The starting motor is protected from continuous starting. For example, if an operator is holding the key in the Start position after the engine starts, the starting motor solenoid will disengage after engine speed reaches 300 rpm.