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Figure 11-19. Exploded View of Gear Reduction Starter Motor
11-35. STARTING MOTORS.
11-36. DESCRIPTION. (See Figure 11-19.) The gear reduction starting motor consists of six major components:
The Commutator End Head Assembly, The Armature, The Frame and Field Assembly, The Gear Housing, The
Pinion Housing, and The Bendix Drive Assembly.
11-37. OPERATION. When the starting circuit is energized battery current is applied to the starting motor
terminal. Current flows through the field coils, creating a strong magnetic field. At the same time, current flows
through the brushes to the commutator, through the armature windings to ground. The magnetic force created in
the armature combined with that created in the field windings begins to turn the armature.
The gear cut on the drive end of the armature shaft extends through the gear housing, where it is supported by
a roller bearing. The gear mates with the teeth of the reduction gear that drives the bendix shaft. The shaft is
keyed to the reduction gear. The Bendix drive is held in position on the shaft by a"spirol" pin. The shaft is
supported in the gear housing by a closed end roller bearing and in the pinion housing by a graphitized bronze
bearing.
When the armature turns the reduction gear, the Bendix drive pinion meshes with the flywheel ring gear by
inertia and action of the screw threads within the Bendix sleeve. A detent pin engages in a notch in the screw
threads which prevents demeshing if the engine fails to start when the starting circuit is denergized.
When the engine reaches a predetermined speed, centrifugal action forces the detent pin out of the notch in
the screw shaft and allows the pinion to demesh from the flywheel.
374
BENDIX DRIVE SHAFT
BENDIX DRIVE
NEEDLE BEARING
GEAR
RETAINER PLATE
*
*
BRONZE BEARING
PINION HOUSING ASS'Y
GEAR HOUSING ASS'Y
FRAME AND FIELD ASS'Y
NEEDLE BEARINGS
BUSHING SET
ARMATURE
SEALED BALL BEARING
COVER BAND
BRUSH SPRING SET
BRUSH SET
C. E. HEAD ASS'Y
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
ELECTRICAL SYSTEM
2D15