When the engine starts, pinion overrun
5. MOTOR: I f t h e b a t t e r y , w i r i n g a n d
protects the armature from excessive
switches are in satisfactory condition,
speed u n t i l t h e s w i t c h i s o p e n e d , a t
and the engine is known to be function-
which time the return spring causes the
i n g p r o p e r l y , remove the motor and fol-
pinion to disengage.
l o w the test procedures outlined below.
A cranking period for all types of start-
A cranking motor is designed for inter-
mittent duty only, and should never be
ing motors should never exceed 30 sec-
operated for more than 30 seconds at a
onds without stopping to allow the motor
time.
After 30 seconds, the cranking
to cool.
If over-cranking should occur,
the thermostat will open and the crank-
must be stopped for at least two minutes
to allow the motor to cool. The same rule
ing cycle will stop to protect the motor.
applies to a motor with a thermostat.
After the cranking motor cools (usually 1
The thermostat is an added protection
to 6 minutes) the thermostat will close
against damage from overcranking.
and then a new starting attempt can be
made.
W i t h t h e c r a n k i n g motor removed from
the engine, the armature should be
checked for freedom of rotation by pry-
Troubleshooting
ing the pinion with a screwdriver. T i g h t
bearings, a b e n t a r m a t u r e s h a f t , o r a
If the cranking system is not performing
loose pole shoe screw will cause the ar-
properly, make the following checks to
m a t u r e t o n o t t u r n f r e e l y . If
the
determine which part of the circuit is at
armature does not turn freely, the motor
fault.
should be
disassembled
immediately.
However,
if the armature does rotate
1. BATTERY: Using a voltmeter and hy-
freely, the motor should be given a no
drometer check the condition of the bat-
l o a d test before disassembly.
Make sure the battery is fully
tery.
switches,
and
charged.
The wiring,
cranking motor cannot be checked if the
battery is defective or discharged.
No Load Test
Connect a voltmeter from the motor ter-
2. WIRING: Inspect the wiring for dam-
minal to the motor frame, and use a RPM
age.
Inspect a l l c o n n e c t i o n s t o t h e
indicator to measure armature speed (see
cranking
solenoid,
magnetic
motor,
Connect
switch, starter switch and battery, in-
the motor and an ammeter in series with
cluding all ground connections.
Clean
a fully charged battery of the specified
and tighten all connections as required.
voltage, and a switch in the open posi-
The cranking system cannot operate
tion from the solenoid battery terminal to
properly with excessive resistance in the
Close the
the solenoid switch terminal.
circuit.
switch and compare the RPM, current
and voltage reading with the specifica-
3. MAGNETIC SWITCH, SOLENOID AND
t i o n s shown i n T a b l e 1 0 D - 1 o n p a g e
CONTROL SWITCHES: Inspect all switch-
It is not necessary to obtain the
10D-3.
es to determine their condition.
From
e x a c t voltage specified as an accurate in-
machine w i r i n g d i a g r a m ( F i g u r e
the
terpretation can be made by recognizing
10A-1 and 10A-2), determine which cir-
that if the voltage is slightly higher the
should be energized with the
cuits
RPM wilt be proportionately higher, with
starting switch closed.
Use a voltmeter
current remaining essentially unchanged.
to detect any open circuits.
However, if the exact voltage is desired,
a carbon pile connected across the bat-
OVERCRANK
4. THERMOSTAT, OR
t e r y can be used to reduce the voltage to
PROTECTION: To check the thermostat
the specified value. Connect the carbon
for continuity, detach wiring harness
pile to only one of the 12 volt batteries.
connector and connect an ohmmeter to
If the specified current draw does not
the two thermostat terminals on the motor
include the solenoid, d e d u c t f r o m t h e
(see Figure 10D-2 on page 10D-3). The
ammeter r e a d i n g t h e s p e c i f i e d c u r r e n t
If not,
ohmmeter s h o u l d r e a d zero.
draw of the solenoid hold-in winding.
DO NOT
thermostat is open circuit.
Make disconnection only with the switch
check thermostat hot, since it is sup-
Interpret the test results as fol-
open.
posed to be open-circuit above certain
lows :
temperatures.
