TM 5-4310-354-14
2. Shorted armature. This can be further
checked on a growler after disassembly.
3. Grounded armature or fields.
Check
further after disassembly.
(c) Failure to operate with high current draw
indicates:
1. A direct ground in the terminal or fields.
2. Seized bearings (this should have been
determined by turning the armature by
hand).
(d) Failure to operate with no current draw
indicates:
1. Open field circuit. This can be further
TS5-4310-354-14/7-9
checked after disassembly by inspecting
internal connections and tracing circuit
Figure 7-9. Starting motor assembly, no-load test setup.
with a test lamp.
(2) Close the switch and note the rpm, current, and
2. Open armature coils.
Inspect the
voltage readings. These should be 8000-13000
commutator for badly burned bars after
rpm, 40-140 amperes, 9 volts.
It is not
disassembly.
necessary to obtain exactly 9 volts, as an
accurate interpretation can be made by
3. Broken brush springs, worn brushes, high
recognizing that if the voltage is slightly higher,
insulation between commutator bars or
the rpm will be proportionately higher, with
other causes which would prevent good
current remaining essentially unchanged.
contact between the brushes and
commutator.
(3) If the exact voltage is desired, a carbon pile
(e) Low no-load speed and low current draw
connection across the battery can be used to
indicate:
reduce the voltage to the specified value.
1. High internal resistance due to poor
(4) Make disconnections only with the switch open.
connections,
defective
leads,
dirty
Interpret the test results as follows:
commutator and causes listed under (d)
above.
(a) Rated current draw and no-load speed
indicate normal condition of motor.
(f) High free speed and high current draw indicate
shorted fields. If shorted fields are suspected,
(b) Low free speed and high current draw
replace the field coil assembly and check for
indicate:
improved performance.
1. Too much friction-tight, dirty, or
c. Disassembly. Disassemble the starting motor
worn bearings, bent armature shaft
assembly in the numerical sequence shown in figure 7-
or loose pole shoes allowing
10 and the following detailed instructions.
armature to drag.
7-9
