Section VI
Paragraphs 6-26 to 6-33
Slight pitting can be removed by use of commutator
c. Recalibrate the attenuator (paragraph 6-40).
dressing sticks of pumice grade by holding the end of
6-29. REPLACEMENT OF TUNING SLUGS. In the
the stick against the commutator face and exerting
slight pressure while the dynamotor is running. This
event that the powdered iron slugs become cracked
should be followed by canvas cloth polishing. If com-
or broken, replace the slugs using the following pro-
mutators are seriously worn or scored, they must be
cedure.
refinished by a properly equipped repair station.
a. Rotate the broken slug stud clockwise until the
slug and stud drop down through the hole in the top of
the tank assembly.
dynamotor brushes be binding in the brush holders,
b. Insert a new slug through this same hole and,
clean the brushes by wiping with a clean cloth damp-
while holding the slug stud against the movable table
ened in unleaded gasoline. If this process does not
with a small round rod, use a screwdriver to rotate
correct the binding, thin the brushes down with No.
the slug counterclockwise until the threads catch.
0000 sandpaper.
C . Check the slug table spring tension by selecting
135 mc (the slug table in extreme upward position)
and checking to be certain that the rollers are tight
Do not allow the sandpaper to touch the contact
surface of the brushes. Do not round off or
against the cams. They must be tight enough so that
vibration will not cause the slug table to move and as
chip off contact edges. Carefully remove
a result change the positions of the slugs in the coils.
abrasive and carbon dust.
6-30. DYNAMOTOR DISASSEMBLY AND ASSEMBLY
Replace brushes that are cracked, damaged, or worn
PROCEDURE. The only disassembly that should be
beyond the minimum length of one-fourth inch. If new
undertaken is the removal of brushes and bearings.
brushes are installed, refer to paragraph 6-33 for
To disassemble this part of the dynamotor proceed as
brush setting procedure.
follows.
.
a. Disconnect the three dynamotor leads f rom under-
side of chassis.
a. Place a strip of No. 000 sandpaper between the
brush and the commutator, with the abrasive side
b. Remove four screws mounting dynamotor to chas-
facing the brush.
sis and lift dynamotor from chassis.
b. Apply only normal brush pressure. The sand-
C.
Remove the end cover screw and pull off covers.
paper strip must be held snugly to the commutator so
that it will have exactly the same curvature as the
d. Remove fan by loosening Bristo set screws.
commutator. The strip should be drawn through in
the direction of normal rotation.
e . Remove screws holding the bearing retainer
plates on the high and low voltage ends.
f. Remove two end bell assemblies after discon-
necting the attached wires.
D o not move the strip back and forth.
g. Remove ball bearing assemblies.
c. Relieve the brush pressure and repeat b above
as often as is required to form the brush face to seat
h. Do not disassemble the dynamotor any further.
75 percent in the direction of rotation and 90 percent
of the width of the brush. Do not round off or chip the
i. To reassemble the unit, reverse the above pro-
contact surface edge. Any loose abrasive or carbon
cedure.
dust should be carefully removed.
.
d. Following the fitting, a light application of a spe-
slight grooving of the commutators is not unusual
cial brush seating stone may be used to smooth out any
after several hundred hours operation and may be
grooves left by the abrasive.
considered as normal. If, however, it is desired to
repolish the commutators, they may be polished with
grade 000 or finer sandpaper.
NOTE
After installing new brushes, the dynamotor
should be run in at normal load for a few hours
Do not use emery cloth on the commutators.
to obtain the polished brush surface necessary
The abrasive is conductive and may cause
for good commutation. Noisy and inefficient
short circuits in the armature by becoming
operation may be experienced until the brushes
imbedded in the slots between the bars.
are properly worn in.
