TM 55-6115-498-40
a.. General.
(1) Replace all parts that are worn or dam-
(2) Relace electrical contact brushes (8,
each overhaul.
(3) Replace all wiring having burned, dis-
colored or cracked insulation, or broken or cor-
roded terinals.
b. Armature Assembly. Replace armature as-
sembly (45, figure 3-1) if any of the following
renditions exist:
(1) If the shaft diameter is less than
0.9843 inch.
(2) If the commutator has badly burned
bars, because such a conditon is usually the
result of open-circuited armature coils.
(3) If commutator bars are loose or out of
alignment.
(4) If resurfaciing the commutator (para-
graph c blow) would reduce the outside di-
ameter below the specified minimum of 2.800
inches. This diameter is indicated by a step cut
into the edge of the commutator.
(5) If the insulation breakdown test (table
between
bars
and
shaft
(ground) shows indication of insulation break-
down.
CAUTION
When performing insulation breakdown
test, keep test probes outside brush" path
to avoid damaging commutator contact
surface.
c. Resurfacing the Commutator.
(1) To remove oil or carbon film, mount
amatire assemby (39, figure 3-1) in a lathe
and take a single light cut across the face of the
commutator at a speed of approximately 600 sur-
face feet per minute. If the contact surface is
scored, rough, or pitted, take a series of light
cuts at approximately 200 surface feet per min-
ute. A dimond-tipped cutting tool (figure 3-4)
is recommended. The point of the cutting tool
must be held on the centerline of the armature
shaft. (See figure 3-5.) If a Carboloy-tipped
cutting tool (figure 3-6) is used, the point of
the cutting tool must be held 0.031 inch below
the centerline of the armature shaft. The mini-
mum diameter to which the commutator may be
turned down is 2.800 inches. This limit is indi-
cated by a step cut into the commutator. If
necessary to remove metal beyond this point, re-
place the amature assembly.
