the voltage is slightly higher the r.p.m. will be pro-
place the coil assembly and check for improved
portionately higher. w i t h the current remaining
performance.
essentially unchanged However, if the exact volt-
age is desired. a carbon pile connected across the
DISASSEMBLY
battery can be used to reduce the voltage to the
specified value If more than one 12-volt battery is
Normally the cranking motor should be disassem-
used, connect the carbon pile to only one of the 12-
bled only so far as is necessary to make repair or re-
volt batteries If the specified current draw does not
placement of defective parts As a precaution, it is
include the solenoid, deduct from the ammeter read-
suggested that safety glasses be worn when dis-
ing the specified current draw of the solenoid hold-
assembling or assembling the cranking motor.
i n winding Make disconnections only with the
switch open. Interpret the test results as follows
1.
Note the relative position of the solenoid. lever
housing. and nose housing so the motor can be
Interpreting Results of Tests
reassembled in the same manner.
1. Rated current draw and no-load speed indicates
2. Disconnect field coi1 connector from solenoid
normal condition of the cranking motor.
motor terminal. and lead from solenoid ground
terminal
2. Low free speed and high current draw Indicate:
a. Too much friction-tight, dirty, or worn bear-
3. On motors which have brush inspection plates,
ings, bent armature shaft or loose pole shoes
remove the plates and then removes the brush
allowing armature to drag
lead screws. This will disconnect the field leads
from the brush holders
b. Shorted armature. This can be further checked
on a growler after disassembly
4. R e m o v e the attaching bolts and separate the
commutator end frame from the field frame
c Grounded armature or fields Check further
after disassembly.
5. Separate the nose housing and field frame from
lever housing by removing attaching bolts.
3. Failure to operate with high current draw In-
dicates:
Remove armature and clutch assembly from lever
6.
a A direct ground in the terminal or fields.
housing.
b. "Frozen" bearings (this should have been de-
7. Separate solenoid from lever housing by pulling
termined by turning the armature by hand).
apart.
4. Failure to operate with no current draw Indicates
CLEANING
a. Open field circuit. This can be checked after
T h e drive, armature and field should not be
disassembly by inspecting Internal connec-
cleaned in any degreasing tank, or with grease dis-
tions and tracing circuit with a test lamp.
solving solvents, since these would dissolve the lu-
bricant in the drive and damage the insulation in
b Open armature coils lnspect the commutator
the armature and field coils. All parts except the
for badly burned bars after disassembly
drive should be cleaned with mineral spirits and a
brush. The drive can be wiped with a clean cloth.
c. Broken brush springs.' worn brushes, high In-
s u l a t i o n between the commutator bars or
If the cummutator is dirty it may be cleaned with
other causes which would prevent good con-
No. 00 sandpaper. NEVER USE EMERY CLOTH TO
tact between the brushes and commutator.
CLEAN COMMUTATOR
5. Low no-load speed and low current draw Indicate:
BRUSHES AND HOLDERS
a. High Internal resistance due to poor connec-
Inspect the brushes for wear. If they are worn ex-
tions; defective leads, dirty commutator and
cessively when compared with a new brush. they
causes listed under Number 4
should be replaced. Make sure the brush holders
are clean and the brushes are not binding in the
6. High free speed and high current draw lndicate
holders. The full brush surface should ride on the
shorted fields. if shorted fields are suspected. re-
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