d.
After the commutator has been turned or
c. Brush pressure on the commutator is
stoned and undercut, remove the burrs which are always
maintained by means of flat clock-type springs which
formed on the edges of the bar during the process, with
exert pressure on a finger which rests on top of the
a three-cornered cutting tool, round the ends of the
brush.
The brush pressure can be measured by
commutator bars, clean the slots out, and finally polish
attaching a small spring balance to the pressure finger
with fine sandpaper and then blow off with compressed
directly over the brush and pulling straight up in line with
air. Lift the brushes when smoothing a commutator in a
the brush travel until the finger is just lifted clear of the
machine and do not replace until all grit has been
brush. The pressure of the brushes can be checked ill
removed. Never use emery cloth o1' emery paper on a
the above manner with the brushholder in place in the
commutator.
motor. The brush pressure given on the general data,
e. Do not use any lubricant on the commutator as
d. Those brushholders which cannot be easily
there is sufficient amount of graphite in the brushes to
supply all the lubrication required.
reached with the spring balance can be checked by
comparing the "feel" of those brushholder springs with
the "feel" of those checked with the balance.
85. Dismantling and Assembling Motors
e. To remove the brushholder for renewal, or
a. Tools. Special tools required when dismantling
accurate adjustment of the brush pressure, first
the traction motor are shown on figure 17. The shop
disconnect the cable lead from the holder by removing
should be supplied with a set of the special tools which
the tap bolt. When the supporting clamp is loosened,
may be made from the drawing supplied.
the holder may be lifted out.
b. Removal of Traction Motors from Locomotive.
f. To adjust the spring pressure, insert a piece of
(1) Remove the tape from the motor lead
1/8-inch diameter drill rod in the holder in the tension
connectors. Disconnect all of the motor
barrel for the spring requiring adjustment and relieve the
connectors, taking care to see that all
tension on the cotter pin. Remove the cotter pin,
leads are plainly marked so that there will
increase or decrease the tension as required by rotating
be no trouble when the are reconnected.
the tension barrel, aid replace the cotter pin.
(2) Remove the truck center pin and
g. Keep the underside of the brushholder carbon
disconnect the BRAKE, SANDER, and
box within not less than 1/8 inch of the commutator to
any other connections between the truck
reduce the chance of brush breakage. Adjustment can
and cab. Jack the cab up at one end a
be made by loosening the clamping block bolt and
sufficient amount to clear and run the
moving the brushholder to the correct position. A fibre
truck out from under.
sheet of the proper thickness makes a handy gage.
(3) Remove the gearcase by unbolting the
two halves and removing the bolts holding
84. Commutator
the gearcase to the motor.
a. A commutator which is taking on a polish and
(4) Remove the motor axle cap bolts and
shows and shows no signs of wear, does not require any
take off the axle caps. If the cap sticks, it
attention.
can be loosened by tapping a flat cold
b. If the commutator is roughened, badly worn or
chisel into the crack between the cap and
burned, remove and place in a lathe, then turn, grind or
motor frame, first on one side and then
stone to give a uniform surface, after which the mica
the other. Care should be taken to see
must be regrooved with special saws.
that the cap is properly supported by a
helper or "backed up" by blocking when it
c. The mica insulation between the copper
is being loosened in order to prevent its
segments is grooved or undercut initially to a depth of
dropping suddenly and causing personal
3/64 inch; as the commutator wears, or if it is turned or
injury.
ground, maintain the grooves since high mica will spoil
the brush fit and cause sparking. Undercutting can be
done to the best advantage by the use of one of the
small power-driven saws which are built for this purpose.
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