GMC C Series 1993, Repair Manual

Page: 234 / 264

J
DIAGNOSIS
SP STARTER MOTORS 6P3-3
STARTER MOTOR TESTS
Before disassembling the starter motor for repair, the
following tests should be made.
N O T IC E : N e v e r o p e ra te th e s ta r te r m o to r
m o re th a n 3 0 s e c o n d s a t a tim e w ith o u t
p a u s in g to a llo w it to c o o l fo r a t le a s t tr io
m in u te s . O v e rh e a tin g , c a u s e d b y to o m u c h
c ra n k in g , w ill d a m a g e th e S ta rte r m o to r.
I*
Inspect
1. Pinion for freedom of operation in one direction by
turning it on the shaft.
2. Armature for freedom of rotation by prying the pin­
ion with a screwdriver in the direction opposite from
Step 1.
•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 disassembled.
• If the armature does rotate freely, the motor
should be given a no-load test before disas­
sembly.
NO LOAD TEST
Connect a voltmeter from the motor terminal to the
motor frame and an rprri indicator to measure armature
speed (figure 3). Connect the motor and an ammeter in
22. Battery
23. "S” Terminal
24. “ M" Terminal
25. “BAT” Terminal
26. Voltmeter
27. Ammeter
28. Tachometer
29. Load Switch
30. Carbon Pile
F4210
Figure 3— No-Load Test Hookup
series with a fully charged 12-volt battery, and a switch
in the open position. Close the switch and compare the
rpm, current, and voltage readings with the specifica­
tions at the end of this section. It is not necessary to
obtain the exact voltage specified as a good reading
can be made by understanding that if the voltage is
slightly higher the rpm will be slightly higher, with the
current remaining basically 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. Compare the test results as follows:
1. Rated current draw and no-load speed indicates
normal condition of the starter motor.
2. Low free speed and high current draw indicates:
• T o o m u c h f r i c t i o n .
Tight, dirty, or worn bear­
ings, bent armature shaft or loose pole shoes
allowing the armature to drag.
• S h o r t e d a r m a t u r e .
This can be further checked
' on a growler after disassembly^
• G r o u n d e d a r m a t u r e o r f i e l d s .
Check further
after disassembly.
3. Failure to operate with high current draw indicates:
• A
d i r e c t g r o u n d
in the terminal or fields.
• S e i z e d b e a r i n g s .
This should have been noted
by turning the armature by hand.
4. Failure to operate with no current draw indicates:
•
O p e n f i e l d c i r c u i t .
This can be checked after
disassembly by inspecting internal conneptions
and tracing the circuit with a test lamp. -
•
O p e n a r m a t u r e c o i l s .
Inspect the commutator
for badly burned bars after disassembly.
•
B r o k e n b r u s h s p r i n g s , w o r n b r u s h e s .
High
insulation between the commutator bars or oth­
er conditions that would prevent good contact
between the brushes and commutator.
5. Low no-load speed and low current draw indicates
a higher internal resistance due to poor connec­
tions, defective leads, dirty commutator and condi­
tions listed under step 4.
6. High free speed and high current draw indicates
shorted fields. If shorted fields are suspected,
replace the field coil assembly and check for
improved performance.