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The starter converts electricity to mechanical energy in two stages.
Turning on the ignition switch releases a small amount of power from
the battery to the solenoid above the starter. This creates a
magnetic field that pulls the solenoid plunger forward, forcing the
attached shift yoke to move the starter drive so that its pinion gear
meshes with the engine's crankshaft flywheel. When the plunger
completes its travels, it strikes a contact that permits a greater
amount of current to flow from the battery to the starter motor. The
motor then spins the drive and turns the meshed gears to provide
power to the crankshaft, which prepares each cylinder for ignition.
After the engine starts, the ignition key is released to break the
starting circuit. The solenoid's magnetic field collapses and the
return spring pulls the plunger back, automatically shutting off the
starter motor and disengaging the starter drive.
When the starter is not in use, the drive unit is retracted so that
its pinion is disengaged from the flywheel. As soon as the starter is
activated, the forward movement of the solenoid plunger causes the
shift yoke to move the drive in the opposite direction and engage the
pinion and flywheel. The pinion is locked to its shaft by a clutch
that unlocks if the engine starts up and the flywheel begins turning
the pinion faster than its normal speed. By allowing the pinion to
spin freely for a moment, the clutch protects the motor from damage
until the drive is retracted.
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