Brush Holders; Armature - Piper PA-31-350 Maintenance Manual

PIPER AIRCRAFT
T-1020
MAINTENANCE MANUAL
Figure 80-4. Testing Motor Figure
Fields for Grounds
BRUSH HOLDERS.
80-5. No-Load Test
Hook-up
1. To test brush holders, touch one test probe to the brush plate and the other to each brush holder.
2. The test lamp should light when the grounded brush holders are touched and should not light when the
insulated brush holders are touched.
ARMATURE.
1. Check the commutator for uneven wear, excessive glazing or evidence of excessive arcing. If only
slightly dirty, glazed or discolored, the commutator can be cleaned with 00 or 000 sandpaper. If the
commutator is rough or worn, it should be turned in a lathe. (Refer to Figure 80-2.) The armature shaft
should be inspected for rough bearing surfaces and rough or damaged splines.
2. To test the armature for grounds, a set of test probes connected in series with a 110 volt light should be
used. Touch one probe to a commutator segment and the other to the armature core. If the test lamp
lights, the armature is grounded and should be replaced.
3. To test for shorted armature coils, a growler is used. (Refer to Figure 80-3.) The armature is placed on
the growler and slowly rotated by hand while a steel strip is held over the core so that it passes over
each armature core slot. If a coil is shorted, the steel strip will vibrate.
4. A quick check for opens can be made by inspecting the trailing edge (in direction of rotation) of the
commutator segments for excessive discoloration. This condition indicates an open circuit.
4116
80-10-08
Page 80-04
Issued: September 2, 1981