Field Coils - Piper SENECA II Service Manual

PIPER SENECA
II
SERVICE MANUAL
Figure 11-16. Turning Motor Commutator
Figure 11-17. Testing Motor
Armature for Shorts
11-33. BR US HES. 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.
11-34. 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. lf the
commutator is rough or worn, it should be turned in a lathe. (Refer to Figure 11-16.)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 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.
c.
To test for shorted armature coils. a growler is used. (Refer to Figure 11-17.) 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.
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.
11-35. FIELD COILS.
a. Check the field coils for grounds (refer to Figure 11-18) by placing one test probe on the frame
and the other on the starter terminal. Be sure the brushes are not accidentally touching the frame. If the
lamp lights, the fields are grounded. Repair or replace.
b. Inspect all connections to make sure they are clean and tight and inspect insulation for
deterioration.
Reissued: 10/11/79
ELECTRICAL SYSTEM
2Gl8