Armature - Piper Navajo PA-31 Service Manual

375
376 A
Figure 11-40.
Turning Starting
Figure 11-41. Testing Motor
Motor Commutator
Armature for Shorts
d. To remove the roller
bearings from the gear housing, use an arbor press
and the correct
bearing arbor.
DO NOT HAMMER OUT.
Each part
should be
cleaned and inspected for excessive
wear or damage. Bearings should be checked
for proper clearance
and evidence of roughness
orgalling.
Oil and dirt should be
removed from insulation
and the condition of the insulation checked.
11-65. BRUSHES. Check the brushes
to see that they slide freely in their hold-
ers and make full contact on the commutator.
If worn to half their original
length
or less, they should be replaced.
11-66.
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
11-40. 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
11-41 .) 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.
Reissued: 10/12/79
.
ELECTRICAL SYSTEM
PIPER NAVAJO SERVICE MANUAL
4C20