Figure 11-20 Turning Motor Commutator
Figure 11-21 Testing Motor Armature for Shorts
11-42. BRUSHES. Check the brushes to see that they slide freely in their holders and make full contact on the
commutator. If worn to half their original length or less, they should be replaced.
11-43. ARMATURE.
a. 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 11-20. The armature shaft should be inspected for rough
bearing surfaces and rough or damaged splines.
b. To test the armature for grounds, a set of test probes connected in series with a I10 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.
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.
d. 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.
11-44. FIELD COILS. (See Figure 11-22).
a. Check the field coils for grounds by placing one test probe on the frame and the other on the starter
terminal. Be sure the brushes are not accidently touching the frame. If the lamp Iights, the fields are grounded.
Repair or Replace.
b. Inspect all connections to make sure they are clean and tight and inspect insulation for deterioration.
GROWLER
376A
376
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
ELECTRICAL SYSTEM
2D17
