Lock-Torque Test Check; Cranking Motor Disassembly - Piper PA-24 Comanche Service Manual

FIGURE 9-27t. NO-LOAD TEST
PIPER COMANCHE SERV ICE MANUAL
I~
Mn.,
J
9-68. M .. Loed Test Check.
(Refer to Figure
"27t.) Connect the crankinl motor in series
with • fully char.cd battery of the speclfied
volt••• an ammeter capable of reading several
hundred amperes. and a variable resistance.
Also connect a voltmeter as mustrated, from
the motor terminal to the motor frallle. An r.p.m.
indic.tor is nee .... ry to mealure armature
speed. Obtaill the specified voltl!C by varying
the :esistlftce unit. Then relld the current draw
and arlllature speed and cOlllpare these readings
with
the values listed ill the published speci-
fications. Interpret the test results as follows:
a. Rated current draw and no--Ioad speed
indicate normal condition of the cranking motor.
b. Low free speed and high current draw
iIldicate:
1. Too lIIuch friction-tipt. dirty, or
loose pole shoes aUowinc armature to drag.
2. Shorted armature. This can be further checked on a Itowler after disassembly.
3. Grounded amature or fi.lds. Check further .fter disassembly.
c. Failure to operate with hip current draw indicates:
1.
A direct ground in the terminal or fields.
2. "Frozen" bearings (this sbould have been determined by tumina the armature by hand).
d. F ailure to operate with no current draw indicates:
1.
Open field circuit. This can be checked after disasselllbly by inspecting internal con-
nections and tracing circuit with a test lamp.
1. Open armature coils. Inspect the commutator for badly burned bars after disassembly.
3. Broken brush springs, worn brUShes, nigh insulation bet"een the commutator bars or
other causes which would prevent aood contact between the brushes and commutator.
e. Low no·load speed and low current draw indicate:
1.
High internai reslstance due to poor connections, defective leads. dirty commutator and
causes listed under (d).
f. High free speed and high current dra" indicate shorted fields. If shorted fields are sus-
pected. replace the field coil assembly and cheek [or improved pedonnance.
•
•
9-69. Lock-Tonlue T elt Check. (Refer
to
Fipre 9·27\1.) The lock-torque test requires the equip-
:nent Illustrated. A variable resistance with a hip current capacity should be used. The crankini
meter should be securely :Dounted and a brake arm hooked to the drive pinion. Use extreme caution
during this test to make sure the end of the brake am: does not slip off of the pinion when current
is applied. When specified current is applied. the torque can be computed frolll the reading on the
scale. A one foot brake arm will directly indicate pound-feet. COlllpare the pound-feet of torque
as read on the scale with that listed in the published Specifications. If the torque is tow. the
motor must be disassembled for further tests and repair.
•
9-;'0. Disassembly. If the motor does 'not perform in accordance with published specifications.
it may need to be disassembled for further teStinl of the components.
~ormaUy
the cranking motor
ELECTRICAL SYSTEM
ISSUED: 8118n2
3 ell