(8) Check for gr unds by checking the armature
o
with a test lamp. Place one probe of the
(2) Check the size of the brushes; replace them
test lamp on the armature core and the
if they are less than one-half inch in length.
other on each commutator bar in turn. If the
(3) Inspect the armature commutator for
test lamp lights, the armature is grounded.
roughness, out-of-round, or high mica. If
If grounded, clean it thoroughly and recheck
any of these conditions exist, turn the
for grounds. If ground cannot be corrected,
commutator down on a lathe and undercut
replace the armature.
the mica 12 inch. Remove only enough
(9)
Check the field coils for grounds by
stock to make the commutator smooth and
checking the coils with a test lamp. Place
round.
After undercutting, finish the
one probe of the test lamp on the field
commutator with No. 00 sandpaper. Clean
frame assembly and the other on the field
all particles from the commutator and
coil leads. If the test lamp lights, the field
armature
using
low
pressure,
dry,
coils are grounded. Replace the field coils
compressed air. Check the armature for
if a ground is indicated.
short circuits as described in (6), below.
(10) Check the field coils for open circuits by
checking with a test lamp. Connect the
Caution
probes of the lamp to the two leads from
Always blow particles off the
the coils. If the lamp does not light, the
commutator in the direction away
coil is open. Replace the field coils if the
from the armature windings.
circuit is open.
(4) Check the brush holders for distortion,
d. Assembly Assemble the generator in reverse
.
cracks, breaks, or other damage; replace
order of disassembly.
damaged brush holders.
e. Installation Install the generator (para 66
.
d).
(5) Replace the brush springs if tension is less
109. Starting Motor Repair
than 28 ounces.
(6) Check for short circuits in the armature by
a. Removal. Remove the starting motor (para 69
rotating the armature on a growler with a
a).
steel strip such as a hacksaw blade held
b. Disassembly Disassemble the starting motor in
.
firmly on the armature. The steel strip will
order of the index numbers assigned to figure 47. Do
vibrate on the area of the short circuit.
not remove the field coils unless tests indicate them to
Short circuits usually are caused by
be defective.
particles between commutator bars. If short
c. Cleaning, Inspection, and Repair.
circuits are found, clean spaces between the
(1) Clean the armature, field frame assembly,
commutator bars using an undercutting tool
and solenoid switch assembly with a cloth
and cleaning thoroughly with compressed
lightly dampened in an approved cleaning
air. If a short circuit cannot be corrected,
solvent.
replace the armature.
(2) Clean all other parts of the starting motor,
(7) Check for open circuits by inspecting for
except the brushes, in an approved cleaning
loose connections at the points where the
solvent; dry thoroughly with compressed air.
conductors
are
connected
to
the
(3) Check the size of the brushes; replace them
commutator risers. Open circuits can be
if they are less than 1182 inch in length.
checked electrically by determining if
(4)
Inspect the armature commutator for
exists
between
adjacent
roughness, out-of-round or high mica. If
commutator bars. Continuity must exist.
any of these conditions exist, turn the
Open circuits cause arcing and burning of
commutator down on a lathe and undercut
the commutator. If the bars are not badly
the mica 12 inch. Remove only enough
burned, resolder the leads and turn the
stock to make the commutator smooth and
commutator down on a lathe. Undercut the
round.
After undercutting, finish the
mica and test for short circuits as described
commutator with No. 00 sandpaper. Clean
in (6) above. If the open circuit cannot be
corrected, replace the armature.
TAGO 6358-A
63
