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TM 10-3930-671-24
Diagnosis of results: With the engine cranking, a
voltmeter reading of more than 2 volts indicates
excessive resistance in solenoid circuit. For example,
the solenoid is good if the voltage drop is 0.1-1.25 volts.
Voltage readings of 1.25 volts and higher indicate faulty
connections, wiring, switches, or starter relay. Check the
wiring, connections, and switches in this portion of the
circuit.
Starter Removal May Be Necessary
If all other components of the starting system (battery,
starter solenoid, starter relay, switches, and wiring) are in
satisfactory condition, and the engine is known to be
functioning correctly, but starter does not operate or
operate correctly, the starter may have to be removed
from the engine for further testing and repair or
replacement.
Starter Motor Inspection
With the starter removed from the engine, the pinion
should be checked for freedom of operation by turning it
on the screw shaft. The armature 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 disassembled without further tests. However,
if the armature does rotate freely, the motor should be
given a no-load test before disassembly.
Starter No-Load Test
• Be sure switch is OPEN before
connections or disconnections are
made.
• Do not apply voltage above what is
specified. Excessive voltage may
cause
the
armature
to
throw
windings.
NOTE
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
current
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.
To obtain full performance data on a
starter motor or to determine the
cause of abnormal operation, the
motor should be subjected to a "no-
load" test. This test is performed, as
described below, with the starter
removed from the engine.
The no-load test may point to specific defects which can
be verified with tests when disassembled. Also, the no-
load test can identify open or shorted fields, which are
difficult to check when disassembled. The no-load test
also can be used to indicate normal operation on a
repaired motor before installation.
No-Load Test Procedure
To perform the no-load test, connect the starter motor in
series with a fully-charged 12-volt battery, as described
below. Use an RPM indicator to measure armature
speed. Then read the current draw and the armature
speed and compare these readings with the values listed
in the motor specifications.
F-309
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