Shift Mechanism - IBM Selectric I/O Reference Manual

SHIFT MECHANISM
1. Shift Cam Back-Up Roller - Adjust the back-up roller
eccentri c left or right so that .001" to .003" of the cam
bearing extends beyond the cam (Fig. 27). The eccen-
tric should be kept in the bottom half of its orbit.
The set screw for the back-up roller eccentric is acces-
sible through a hole in the cam with the cam in the low-
er case position.
Adjust Back-Up
Ro Iler Eccentri c
FIGURE 27. Shift Cam Back-Up Roller Adjustment
If the bearing did not extend beyond the cam, the shift
clutch arbor could rub against the cam and create a
noise as well as a drag on the cam when the cam was
stati onary •
Two problems could be created by having too much of the
bearing extending beyond the cam. A gap would exist
between the cam and the shift clutch arbor. This could
allow a coil of the shift clutch spring to wedge into the
gap and lock the machine. If the back-up roller were
excessively far to the left, the cam would be forced to
the left at the rear causing it to cock and bind at the
pivot.
The shift clutch mechanism including the arbor should be
removed in order to best observe the adjustment. Be sure
that.002" to .004" end play exists in the operational
shaft when the arbor is replaced.
CAUTION: Any change in the position of the back-up
roller directly affects the typehead homing and the shift
Clutch Spring
Retaining Plate
FIGURE 28. Shift Clutch Spring Retaining Plate
cause failure of the cam to reach the detented position
l
because the spring would be expanded too soon. Insuf-
ficient expansion would allow the clutch spring to drag
when at rest creating a load on the motor and on the
shift release mechanism.
A. REST POSITION
arm motion adjustments. Be sure to recheck these ad- .028 11 to .059
11
justments.
2. Shift Clutch Spring Retaining Plate - Adjust the retain-
ing plate attached to the shift cam (Fig. 28) to satisfy
the following condition. With the machine turned OFF
and the shift cam detented, the shift clutch ratchet
should rotate .028
11
to .059" when the shift release arm
releases the ratchet. The rotation can be observed rela-
tive to the shift interlock (Fig. 29B). Half the distance
from the center of one ratchet tooth to the next is 3/64
11
or
.04r.
The adjustment of the retaining plate determines how
much the clutch spring will be expanded when the shift
mechanism is at rest. Expanding the spring too much may
2-7
FIGURE
29.
Shift Clutch Spring Retaining Plate Adjustment
NOTE: If sufficient adjustment cannot be obtained with
the retaining plate, the right end of the clutch spring
may be placed in another hole in the ratchet. The ad-
justment can then be refined with the plate.
3. Shift Cam Stop - Adjust the stop so that the shift clutch
ratchet has .010 11 to .030" rotary motion between the
shift cam stop and the shift release arm with the mech-
anism at rest (Fig. 30).
The adjustment insures that the shift cam will not be al-
lowed to trove! past the detented position.