allowed to run free to the point where they will
destroy themselves.
SIX WINDINGS, SERIES-PARALLEL—
Three pairs of series-wound field coils provide
the magnetic field for a heavy-duty starter
motor. This configuration uses six brushes.
THREE WINDINGS, TWO SERIES, ONE
SHUNT—The use of one filled coil that is
shunted to ground with a series-wound motor
controls motor speed. Because the shunt coil is
not affected by speed, it will draw a steady heavy
current, effectively limiting speed.
DRIVE END FRAME.—The drive end frame is
designed to protect the drive pinion from damage and
to support the armature shaft. The drive end frame of
the starter contains a bushing to prevent wear between
the armature shaft and drive end frame.
Types of Starting Motors
There are two types of starting motors that you will
encounter on equipment. These are the direct drive
starter and the double reduction starter. All starters
require the use of gear reduction to provide the
mechanical advantage required to turn the engine
flywheel and crankshaft.
DIRECT DRIVE STARTERS.—Direct
drive
starters make use of a pinion gear on the armature shaft
of the starting motor. This gear meshes with teeth on
the ring gear. There are between 10 to 16 teeth on the
ring gear for every one on the pinion gear. Therefore,
the starting motor revolves 10 to 16 times for every
revolution of the ring gear. In operation, the starting
motor armature revolves at a rate of 2,000 to 3,000
revolutions per minute, thus turning the engine
crankshaft at speeds up to 200 revolutions per minute.
DOUBLE REDUCTION STARTER.—The
double reduction starter makes use of gear reduction
within the starter and the reduction between the drive
pinion and the ring gear. The gear reduction drive head
is used on heavy-duty equipment.
Figure 2-42 shows a typical gear reduction starter.
The gear on the armature shaft does not mesh directly
with the teeth on the ring gear, but with an intermediate
gear which drives the driving pinion. This action
provides additional breakaway, or starting torque, and
greater cranking power. The armature of a starting
motor with a gear reduction drive head may rotate as
many as 40 revolutions for every revolution of the
engine flywheel.
Figure 2-42.—Gear reduction starter.
NEUTRAL SAFETY SWITCH
Vehicles equipped with automatic transmissions
require the use of a neutral safety switch. The neutral
safety switch prevents the engine from being started
unless the shift selector of the transmission is in
NEUTRAL or PARK. It disables the starting circuit
when the transmission is in gear. This safety feature
prevents the accidental starting of a vehicle in gear,
which can result in personal injury and vehicle
damage.
The neutral safety switch is wired into the circuit
going to the starter solenoid. When the transmission is
in forward or reverse gear, the switch is in the OPEN
position (disconnected). This action prevents current
from activating the solenoid and starter when the
ignition switch is turned to the START position. When
the transmission is in neutral or park, the switch is
closed (connected), allowing current to flow to the
starter when the ignition is turned.
A misadjusted or bad neutral safety switch can
keep the engine from cranking. If the vehicle does not
start, you should check the action of the neutral safety
switch by moving the shift lever into various positions
while trying to start the vehicle. If the starter begins to
work, the switch needs to be readjusted.
To readjust a neutral safety switch, loosen the
fasteners that hold the switch. With the switch
loosened, place the shift lever into park (P). Then,
while holding the ignition switch in the START
position, slide the neutral switch on its mount until the
engine cranks. Without moving the switch, tighten the
fasteners. The engine should now start with the shift
lever in park or neutral. Check for proper operation
after the adjustment.
If by adjusting the switch to normal operation is
not resumed, it may be required to test the switch. All
that is required to test the switch is a 12-volt test light.
2-29
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