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GEK-95352
18
is obtained. The nut should then be
locked with its lockwasher. If
equipment is not available to use
this method, the following proce-
dure may be used. Tighten the mo-
tor shaft nut carefully until all end-
play is removed and the rotor just
fails to turn freely. Then back the
nut off 1/6 turn and lock with its
washer. An assembly nameplate
giving this information is mounted
on the motor.
Motors which must withstand con-
tinuous up-thrust have a somewhat
different construction. The upper
(thrust) bearing is arranged to take
this up-thrust; it consists of angular-
contact thrust bearing mounted
back-to-back (DB). (See Figure 3.)
The inner rings are locked on the
lower half-coupling with a nut and
the outer rings are clamped in the
endshield with a ring. The shaft
shoulder below the lower half-
coupling is so located that it seats
against the lower half-coupling be-
fore the lower bearing comes up
against its cover. No special adjust-
ment is necessary when reassem-
bling this type of motor, and the
motor shaft nut can be pulled down
tight and locked. The end-play of
motors using DB-mounted bearings
will then be very small, 0.005” or
less.
3. End-Play Adjustment
Roller-Thrust Bearing
Springs are used under spherical-
roller thrust bearing to keep them
axially loaded during momentary
up-thrust periods. See Figure 2. This
puts an up-thrust load on the lower
guide bearing. The springs (and
spacers if a full circle of spring is
not used) are located in a “chair”
which is in turn located in the upper
endshield. This ”chair” and the cap-
tive springs can be removed and
cleaned as a unit if necessary; it
should not be taken apart unless it or
a spring is damaged.
End-play is provided in the motor so
that the application of down-thrust
during normal operation will cause
the thrust bearing to move down and
seat in its housing and relieve the
up-thrust load on the lower bearing.
Thus, to avoid premature failure of
the lower bearing, the minimum to-
tal external down-thrust that is ap-
plied continuously to the motor
during operation should always be
greater than the spring-load listed on
the individual outline provided with
the motor. This value may range
from 3000 pounds to 6000 pounds,
depending on the size of the bear-
ing.
Adjust the end-play by adjusting the
motor shaft nut. Tighten the nut un-
til the lower bearing comes up
against its cover and the springs are
being compressed, as indicated by
downward movement of the lower
half-coupling. Check the end-play
by placing a dial indicator between
the end-shield cover and the lower
half-coupling and pressing down on
the latter with a jack (sec Figure 2)
until the bearing seats in its housing.
Repeat this process of tightening the
nut and checking the end-play until
0.015 to 0.020” end-play is ob-
tained; then lock the nut with the
setscrew.
There are six holes in the nut and
five holes in the lower half-
coupling, making a total of 30
“locking positions” where two holes