GMC 1976 ZEO 6083 Maintenance Manual page 441

operated shift lever slides the pinion into mesh with
the flywheel ring gear teeth. The rotary motion be-
tween the pinion and ring gear, provided by spiral
splines on armature shaft, normally relieves tooth
abutment on the first attempt to engage pinion and
the engine flywheel ring gear . When the engine is
started, pinion overrun protects the armature from
excessive speed until the ignition or control switch is
released, at which time the solenoid shift lever return
spring causes the pinion to disengage. To prevent
excessive overrun on vehicles equipped with these
starting motors, the ignition or control switch must
be released immediately when engine starts .
TROUBLE DIAGNOSIS
Wiring : Inspect the wiring for damage . Inspect all
connections to the cranking motor, solenoid or mag-
netic switch, ignition switch or any other control
switch, and battery, including all ground connec-
tions. Clean and tighten all connections as required .
Magnetic Switch or Solenoid and Control Switches : In-
spect all switches to determine their condition. Con-
nect a jumper lead around any switch suspected of
being defective. If the system functions properly us-
ing this method, repair or replace the bypassed
switch .
Motor: If the battery, wiring and switches are in
satisfactory condition, and the engine is known to be
functioning properly, remove the motor and follow
the test procedures outlined .
Never operate the cranking motor more than 30
seconds at a time without pausing to allow it to cool
for at least two minutes. Overheating, caused by
excessive cranking will seriously damage the crank-
ing motor.
STARTER REMOVAL
1 .- Disconnect batteries by removing ground
straps and hoist vehicle.
2. Remove two attaching bolts and move starter
for easier access to wires.
3 . Note the position of the wires and disconnect
the wires from starter.
4. Remove the starter.
CRANKING MOTOR TESTS
With the cranking motor removed from the en-
ENGINE ELECTRICAL
6Y- 6 1
gine, the pinion should be checked for freedom of
operation by turning it on the screw shaft. The arma-
ture should be checked for freedom of rotation by
prying the pinion with a screwdriver. Tight bearings,
a bent armature shaft, or a loose pole shoe screw will
cause the armature to not turn freely . If the armature
does not turn freely the motor should be disassem-
bled immediately . However, if the armature does ro-
tate freely, the motor should be given a no-load test
before disassembly.
NO-LOAD TEST (FIGURE 66)
Connect a voltmeter from the motor terminal to
the motor frame, and use an rpm indicator to meas-
ure armature speed. Connect the motor and an amm
eter in series with a fully charged battery of the
specified voltage, and a switch in the open position
from the solenoid battery terminal to the solenoid
switch terminal . Close the switch and compare the
rpm, current, and voltage readings with the specifi-
cations at the end of this section.
It is not necessary to obtain the exact voltage
specified, as an accurate interpretation can be made
by recognizing that if the voltage is slightly higher
the rpm will be proportionately higher, with the cur-
rent remaining essentially unchanged. However, if
the exact voltage is desired, a carbon pile connected
across the battery can be used to reduce the voltage
to the specified value. If the specified current draw
does not include the solenoid, deduct from the amm-
eter reading the specified current draw of the solen-
oid hold-in winding. Make disconnections only with
the switch open . Interpret the test results as follows:
1 . Rated current draw and no-load speed indi-
cates normal condition of the cranking motor .
2. Low free speed and high current draw indi-
cates:
a. Too much friction-tight, dirty, or worn
bearings, bent armature shaft or loose pole shoes
allowing armature to drag .
b. Shorted armature . This can be further
checked on a growler after disassembly .
c. Grounded armature or fields . Check fur-
ther after disassembly.
3. Failure to operate with high current draw indi-
cates:
a. A direct ground in the terminal or fields .
b. "Frozen" bearings (this should have been
determined by turning the armature by hand).