The starting motor is mounted on the flywheel housing
as illustrated in Fig. 1. When the starting circuit is
closed, a small drive pinion on the armature shaft
engages with the teeth on the engine flywheel ring gear
to crank the engine. When the engine starts, it is
necessary to disengage the drive pinion to prevent the
armature from overspeeding and damaging the starting
To accomplish this, the starting motor is
equipped with a heavy-duty sprag overrunning clutch.
Sprag Overrunning Clutch Type Starting Motor
A solenoid switch, mounted on the starting motor
Fig. 1 - Sprag Overrunning Clutch Type Starting
housing, operates the current sprag type overrunning
clutch drive by linkage and a shift lever (Fig. 2). When
An oil seal, between the shaft and the lever housing,
the starting switch is engaged, the solenoid is energized
and a linkage seal (Fig. 2) prevents the entry of
and shifts the starting motor pinion into mesh with the
transmission oil into the main frame of the starting
flywheel ring gear and closes the main contacts within
motor and solenoid case.
Once engaged, the clutch will not
disengage during intermittent engine firing. To protect
the armature from excessive speed when the engine
starts, the clutch "overruns", or turns faster than the
Starting motors which are provided with lubrication
armature, which permits the pinion to disengage itself
fittings (hinge cap oilers, oil tubes sealed with pipe
from the flywheel ring gear.
plugs, or grease cups) should be lubricated periodically
The solenoid plunger and shift lever on this type of
starting motor is totally enclosed to protect them from
dirt, water and other foreign material.
Fig. 2 - Cross-section of Starting Motor with Sprag Heavy-Duty Clutch Drive.