Piper COMANCHE PA-24-180 Service Manual page 541

PIPER COMANCHE SERVICE MANUAL
9-14. Disassembly, Repair And Reessembly. Normally, disassembly should proceed only so far
as is necessary to make repair or replacement of the defective parts. For example, the field coils
should be checked for opens, shorts, or pounds before being removed from the field frame: they
should be removed only if they require repair or replacement.
9-15. Field Coil Removal. Field coils can be removed from the field frame most easily by use
of a pole shoe screw diver. It is also advisable to use a pole shoe spreader, since this prevents
distortion cf the field frame. The pole shoe screw diver permits easy loosening and removal of
the pole shoe screws so that the pole shoes and field coils can be taken out of the field frame.
The pole shoe screw driver and spreader should be used on reassembly of the field frame. Careful
reassembly is necessary to prevent shorting or pounding of the field coils as the pole shoes are
tightened into place.
9-16. Inspection And Repair Of Prts.
a. The armature or field should not be cleaned ', any degreasing tank or by use of degreasing
compounds, since this might damage insulation st
at a shurt or ground would subsequently de-
velop. Sealed ball bearings do not require cleaning or relubrication. Other generator parts should
be cleaned and carefully inspected for wear and other damage. Any defective parts should be
repaired or replaced. On reassembly all soldered electrical connections should be made with
rosin flux. Acid flux must never be used on electrical connections.
9-17. Field Coil.
a. The field coils should be checked for grounds, opens or shorts as already explained in
paragraph 9-10.
b. Grounded field coils may sometimes be repaired by removing them so they can be reinsu-
lated. Care must be used to avoid excessive bulkiness when applying new insulation, since this
might cause the pole shoe to cut through and cause another ground when the coils are reinstalled.
c. Usually, if a field coil is open or shorted internally it will require replacement, since it is
difficult to repair such a defect.
d. To remove or replace field coils in the field frame, the use of a pole shoe spreader and
screw driver is recommended.
9-18. Armature Service.
a. The armature should be checked for opens, shorts and grounds as explained in following
paragraphs. If the armature commutator is worn, dirty, out of round, or has high mica, the armature
should be put in a lathe so the commutator can be turned down and the mica undercut. The mica
should be undercut 1/32 of an inch and the slots cleaned out carefully to remove any trace of dirt
or copper dust. As a final step in this procedure, the commutator should be sanded lightly with
No. 00 sandpaper to remove any slight burrs that might be left as a result of the undercutting
procedure.
b. Open circuited armatures can often be saved when the open is obvious and repairable. The
most likely place an open will occur is at the commutator riser bans: this usually results from
overloading of the generator, which causes overheating and melting of the solder. Repair can be
effected by reseldeing
the leads in the nser bars (using rosin flux) and turning down the com-
mutator in a lathe to remove the burned spot and then undercutting the mica as explained in the
previous paragraph. In some heavy-duty armatures the leads are welded into the riser bars, and
these cannot. of course, be repaired by resoidenng.
ELECTRICAL SYSTEM
ISSUED: 8/18/72
3A19