SECTION 3 - CHASSIS & SCISSOR ARMS
3-24
31215074
Drive Motor Inspection and Service
NOTE:
Refer to Figure 3-15.
1. Carefully blow out any accumulated carbon dust
and dirt from the Commutator End Head (9) and
the Frame & Field Assembly (2) using clean, oil free,
compressed air.
2. Replace Brushes (5) that are worn below their
usable length of 0.6 in (1.5 cm), show signs of
uneven wear or signs of overheating, such as dis
-
colored brush shunts and brush springs. Brushes
should always be replaced in complete sets of four.
Use identical replacement parts; do not substitute
brush grades as the brushes are matched to the
motor type and application to provide the best
service. Substituting brushes of the wrong grade
can cause premature commutator failure and
excessive brush wear.
3. Make sure the Brush Box Assembly (6) is tight on
the commutator end head. Replace brush box
assemblies in the commutator end head if they are
physically damaged or brush holders are loose on
the brush plate.
4. Visually inspect the frame and field assembly for
overheating or other signs of damage. Check all
wiring to ensure that the insulation is in good con
-
dition. Verify that pole screws are torqued to 250 -
300 in-lb (28.2 - 33.9 Nm). Verify field resistance
using a suitable ohmmeter per the appropriate
motor specification. Verify that the field is electri
-
cally isolated from the frame using a dielectric tes
-
ter. Replace as necessary.
5. Visually inspect the Armature Assembly (3) for
signs of overheating or physical damage. Visually
inspect the seal surface of the shaft for excessive
wear. Check for grounded circuits using a dielec
-
tric tester by applying voltage between the com
-
mutator and the shaft. Visually inspect the
commutator for excessive wear and overheating.
Replace as necessary.
6. Visually inspect the brake surfaces for excessive
wear. Replace Brake Assembly (11) if necessary.
7. Visually inspect the Wire Harness (1) for frayed
insulation, loose terminals, or other damage.
Replace as necessary.
Drive Motor Reassembly
NOTE:
Refer to Figure 3-15.
1. After inspection and servicing, reassemble the wir
-
ing in the Commutator End Head (9) as originally
found. Ensure the wiring does not contact metal
parts and that it allows the brushes to move unre
-
stricted in the holders. Motor terminals must be
assembled as shown Figure 3-16. Torque bottom
terminal nut to 110 - 140 in-lb (12.4 - 15.8 Nm).
2. After the motor has been disassembled, it is rec
-
ommended that new bearings be installed
because bearings may have been damaged during
removal. Although the bearings may appear and
feel good, the bearing races could be “brinelled”
(races or balls deformed) and may exhibit noise
and vibration problems or fail within a relatively
short period of service. Press a new bearing into
the commutator end head, pressing on the outer
race only. See Figure 3-16. Replace the Retaining
Ring (7) in the retaining ring groove.
3. Press the Armature (3) commutator end into the
commutator end head and bearing assembly,
carefully supporting the inner-race of the bearing.
See Figure 3-16.
4. Carefully release the Brush Springs (4) allowing the
Brushes (5) to contact the commutator. Make sure
brush shunts do not interfere with spring move
-
ment.
1. Press Fixture must press against Outer Race
2. Bearing
3. End Head (held stationary)
4. Armature Assembly
5. Assembled End Head, Bearing, and Retaining
Ring
6. Press Fixture must press against Inner Race (held
stationary)
Figure 3-16. Bearing Pressure Guidelines
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