ENGINE
ELECTRICAL
6E-3
SERVICE
ARMATURE
W
PIPE
. COUPLING
If
the armature commutator Is worn, dirty, out of
round
or has high insulation, the armature should
be put In a lathe so the commutator can be turned
down. The insulation should then be undercut 1/32"
wide and 1/32" deep, and the
slots
cleaned out to re-
move
any trace of dirt or copper dust. As a final
step
in this procedure, the commutator should be
sanded lightly with No. 00 sandpaper to remove any
burrs
left as a result of the undercutting procedure.
The
armature should be checked for opens, short
circuits
and grounds as follows:
Fig.
6E-2
Driving
Retainer
Off
Snap Ring
CLEAN
AND
INSPECT
1. Test overrunning clutch action. The pinion
should turn freely in the overrunning direction.
Check
pinion
teeth
to see that they have not been
chipped, cracked, or excessively worn. Replace as-
sembly if necessary. Badly chipped pinion
teeth
may
indicate chipped
teeth
on the ring gear.
This
should
be checked under such conditions and replaced if
necessary.
2. Inspect brushes for wear. Replace if worn to
one-half their original length.
Check
brush holders
to see that they are not deformed or bent, but
will
properly
hold brushes against the commutator.
3.
Check
fit of armature shaft in bushing of drive
housing. Shaft should fit snugly in the bushing. If the
bushing is worn, it should be replaced.
4. The overrunning clutch, armature and fields
should not be cleaned in any degreasing tank, or with
grease-dissolving solvents, since
these
would dis-
solve
the lubricants in the clutch mechanism and
would damage the insulation in the armature and
field coils. It is
suggested
that all parts except the
clutch,
be cleaned with oleum spirits and a brush.
The
clutch can be wiped with a clean cloth.
If
the commutator is dirty it may be cleaned with
No. 00 sandpaper. Never use emery cloth to clean
commutator.
1.
Open—
The
most likely place for an open to
occur
is at the commutator riser bars as a result of
excessively long cranking periods. Inspect the points
where the conductors are joined to the commutator
bars
for
loose
connections. The poor connections
cause arcing and burning of the commutator bars as
the starting motor is used. If the bars are not too
badly burned, repair can
often
be
effected
by re-
soldering the leads in the riser bars (using rosin
flux),
and turning down the commutator in a lathe to
remove the burned material. The insulation should
then be undercut.
2. Short
Circuit—Short
circuits in the armature
are
located by use of a growler. When the armature
is rotated in the growler with a steel grip such as a
hacksaw
blade held above it, the blade
will
vibrate
above the area of the armature core in which the
short circuit is located. Shorts
between
bars are
sometimes
produced by brush dust or copper be-
tween the bars. These shorts can be eliminated by
cleaning out the slots.
3.
Ground—
Grounds
in the armature can be de-
tected by the use of 110-volt
test
lamp and
test
points. If the lamp lights when one
test
point is
placed on the commutator with the other point on
the core or shaft (Fig.
6E-3),
the armature is
grounded. Grounds occur as a result of insulation
failure
which is
often
brought about by overheating
of the starting motor produced by excessive long
cranking
periods or by accumulation of brush dust
between
the commutator bars and the steel commu-
tator ring.
FRAME
AND
FIELD
The
field winding can be checked for an open or a
ground by using a
test
lamp as follows:
1. Using a 110-volt
test
lamp, place one lead on
each end of the field coils connected in series (Fig.
6E-4).
If lamp
does
not light, the field coils are
open and must be repaired or replaced.
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