Field Coils; Gear And Pinion Housing; Bendix Drive; Assembly Of Starting Motor - Piper PA-31-350 Maintenance Manual

PIPER AIRCRAFT
T-1020
MAINTENANCE MANUAL
FIELD COILS.
1. Check the field coils for grounds (refer to Figure 80-4) 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.
2. Inspect all connections to make sure they are clean and tight and inspect insulation for deterioration.
GEAR AND PINION HOUSING.
Inspect housings for cracks and bearings for excessive wear. Remove rust, paint or grease from mounting
surfaces.
BENDIX DRIVE.
The Bendix Drive should be wiped clean with a dry cloth. The pinion should turn smoothly in one
direction and should lock in the other direction. Replace drive if it fails to check as above or if the pinion teeth
are excessively worn or damaged.
ASSEMBLY OF STARTING MOTOR.
1. When assembling the starting motor, always use an arbor press and the proper bearing arbor for
installing graphitized bronze and roller bearings. The Bendix shaft should have a thin film of
Lubriplate #777 or equivalent on the Bendix portion of the shaft. End play should be .005 to .050 of an
inch.
2. New brushes should be properly seated when installing by wrapping a strip of 00 sandpaper around the
commutator (with the sanding side out) 1-1/4 to 1-1/2 times maximum. Drop brushes on sandpaper
covered commutator and turn the armature slowly in the direction of rotation. Dust should be blown
out of the motor after sanding.
-NOTE-
The spring tension is 32 to 40 ounces with new brushes. This
tension is measured with the scale hooked under the brush spring
near the brush and the reading is taken at right angles to the line
offorce exerted by the brush spring.
3. Check the position of the pinion to be sure the unit will mesh properly with the flywheel ring gear. See
specifications for unit for correct dimensions.
BENCH TESTS.
1. After the starting motor is reassembled, it should be tested to see that the no-load current at a certain
voltage is within specifications. To make this test, connect as shown in Figure 80-5. If current is too
high, check the bearing alignment and end play to make sure there is no binding or interference. Two
or three sharp raps on the frame with a rawhide hammer will often help to align the bearings and free
the armature.
80-10-13
4117
Page
80-05
Issued: September 2, 1981