Piper COMANCHE PA-24-180 Service Manual page 581

PIPER COMANCHE SERVICE MANUAL
9-68.
No-Load
Test Check. (Refer to Figure
927t.) Conect the cranking motor in series
with
a fully charged battery of the specified
voltage, an ammeter capable of reading several
fications. Interpret the test results as follows:
a. Rated current draw and no-load speed
indicate normalcondition of the cranking motor.
b. Low free speed and high current draw
indicate:
FIGURE 27t. NO-LOAD TEST 1. Too much friction-tight, dirty, or
loose pole shoes allowing armature to drag.
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. "Frozen" 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 checked after disassembly by inspecting internal con-
nections and tracing circuit with a test lamp.
2. Open armature coils. Inspect the commutator for badly burned bars after disassembly.
3. Broken brush springs, worn brushes, high insulation between the commutator bars or
other causes which would prevent good contact between the brushes and commutator.
e. Low no-load speed and low current draw indicate:
1. High internal resistance due to poor connections, defective leads, dirty commutator and
causes listed under (d).
f. High free speed and high current draw indicate shorted fields. If shorted fields are sus-
pected, replace the field coil assembly and check for improved performance.
9-69. Lock-Torque Test Check. (Refer to Figure 9-27u.) The lock-torque test requires the equip-
ment illustrated. A variable resistance
with a high current capacity should be used. The cranking
motor should be securely mounted and a brake arm hooked to the drive pinion. Use extreme caution
during this test to make sure the end of the brake arm does not slip off of the pinion when current
is applied. When specified current is applied, the torque can be computed from the reading on the
scale. A one foot brake arm will directly indicate pound-feet. Compare the pound-feet of torque
as read on the scale with that listed in the published specifications. If the torque is low, the
motor must be disassembled for further tests and repair.
9-70. Disassembly. If the motor does not perform in accordance with published specifications.
it may need to be disassembled for further tesung of the components. Normally the cranking motor
ELECTRICAL SYSTEM
ISSUED: 8/18/72
3C11