Inspection Of Starter Motor - Johnson SKEE-HORSE 25-201R Service Manual

c. Check each armature coil for open circuits by rotating torque
wrench handle through a 180 degree arc after initial torque reading
has been noted. This must be done quickly. Torque should be
uniform through this arc, although reading will decrease slightly
each time brush moves from one commutator segment to another.
If an appreciably wide area is found in which torque is very low,
disassemble starter and check armature.
INSPECTION OF STARTER MOTOR
a. Check armature on a growler for shorted turns
(see
Figure 7-41).
NOTE: Follow operating instructions furnished with armature
growler for proper test procedures. Clean between commutator
segments of armature and recheck armature on growler.
If
shorted turns are still indicated, replace armature.
b. Check armature for grounded windings (see Figure 7-42). Rotate
one lead of continuity tester (test light or meter) around circum-
ference of commutator while holding other continuity meter lead on
the armature core or shaft.
An
indication of continuity means that
the armature windings are grounded and armature must be re-
placed.
c. Check armature for open windings by using an ohmmeter. Meas-
ure reSistance between adjacent commutator segments, using LO
OHMS scale. Rotate leads around entire circumference of com-
mutator.
An
open winding is indicated
if
anyone reading is much
higher (three times higher or more) than the average reading.
d. Inspect commutator segments.
If
they are dirty or show signs of
wear, turn commutator in a lathe until surface is clean and smooth.
e. After turning commutator, undercut inSulation between commutator
segments to a depth of approximately 1/32 inch. The undercut
must be flat at the bottom (triangular groove cuts are unsatisfac-
tory) and should extend beyond the brush contact area for the full
length of each insulated groove (see Figure 7-43).
f. After commutator has been undercut, sand lightly with No. 00 sand-
paper to remove burrs left during the undercutting process. After
sanding, clean commutator thoroughly, removing all traces of
metal chips or sanding grit, and recheck armature on growler.
g. Inspect armature insulation for indications of overheating or dam-
aged windings. Clean off any deposits of carbon which may con-
tribute to later failure of the windings. NOTE: Starter motor
components should not be washed off in cleaning solvents. Most
solvents will soften varnish insulation used on armature and field
windings. All starter motor components can be cleaned ade-
quately with a clean cloth or soft brush. Cleaning end heads in
solvent may dissolve the oils that have impregnated into the arma-
ture shaft bearings. If these oils are removed, bearing or arma-
ture shaft wear can be expected. Cleaning of armature in solvent
will leave oily residue on the commutator segments, causing arCing
between the commutator and brushes.
Brushes
a. Inspect the brushes; replace
if
worn to one-third their original 3/8"
length, or
if
damaged or cracked. Replace brush springs if weak.
b. Inspect brush springs. Springs should have a pressure of 35 to 90
ounces when compressed to 9/32 inch. Measure brush tension with
scale hook under brush screw or under bend in brush spring, and
take reading as brush just leaves commutator. Pull offspring scale
must be directly opposite ,line of force exerted by. brush spring.
7-15
Figure 7-41
Figure 7-42
INCORRECT
CORRECT
Figure 7-43