Lesson 2
Suppose the armature has started to turn, and the pinion, which is not turning because of the
weight on one side, is moving toward the flywheel ring gear. The teeth on the pinion gear have
meshed (engaged) with the teeth on the ring gear. The pinion has reached its stop and cannot
move any further on the threaded sleeve. It is now locked to the sleeve and must turn with it. The
now rotating pinion turns the flywheel gear, which in turn rotates the flywheel ring gear and engine
crankshaft.
As soon as the engine starts, its speed of rotation is faster than that of the pinion. The ring gear
now drives the pinion because it is turning faster. The pinion then moves back on the threaded
sleeve and disengages from the ring gear.
Sometimes the engine starts but fails to continue to run; however, the few turns that it does run
may be enough to force the Bendix drive pinion out of mesh. To keep this from happening, a new
type of Bendix drive is used on some late model vehicles. This drive is called the Bendix Folo-
Thru. Inside the drive is a spring-loaded pin. When the pinion moves to engage the flywheel gear,
the pin enters a notch on the threaded sleeve to hold the pinion in mesh. As long as the engine
turns slowly, the pinion will be held in mesh with the flywheel by the pin in the notch on the
sleeve. After the engine starts and is operating at a speed of about 400 RPM, the pinion, which is
now spinning at a rate of several thousand RPM, will force the pin out of the notch on the sleeve.
The pinion can then move back on the threaded sleeve away from the flywheel.
In the overrunning clutch type starter drive, the pinion is shifted into engagement with the flywheel
with a lever.
The drive for the overrunning clutch has internal (inside) splines which fit external splines on the
starter armature shaft. The drive pinion is attached to a rotor which forms the inner half of the
overrunning clutch.
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