IBM Selectric Reference Manual page 160

10.18 SKIRT CLEARANCE
Whi Ie manually half-cycling a 2 ti It, +5 rotate char-
acter, there should be .025 11 - .035 11 clearance be-
tween the Rotate Detent and any tooth on the type
element. To obtain this clearance, half-cycle any
character and rotate the Detent Actuating Lever
Mounting Stud so that the Detent Actuating Lever is
all the way to the rear, then adjust the detent cam on
the print sleeve for .00111 clearance between the low
dwell of the cam and the cam follower.
Redesigned Detent Actuating Lever and Support
Current production detent actuating levers have been
en larged to accept a larger shou Ider and flange on
the support mounting screw. Using larger washers,
these parts have improved stabi Iity, resulting in re-
duced exposure to breakage and loss of typehead ski rt
clearance.
The part numbers remain unchanged. However, since
the new level parts are not interchangeable with the
former level, field replacement of former support
screws or detent actuating levers wi II require that all
three parts be replaced. B/M 1272176 includes the
following parts:
Part No.
1128493
1128458
1128495
Description
Washer
Lever, Detent Actuati ng
Screw, Detent Actuating Arm
Note: Production machines wi II use a large nut,
PN 1134842, on the top section to the detent act-
uating arm screw. It is not necessary to use this nut
for field installation.
10.19 ADJUSTMENT CHANGES - TILT SELECTION
On gearless tilt machines, adjust the RH tilt pulley
with a 0 ti It, 0 rotate character half-cycled, so that
the ti It detent enters .004 11 - .008 11 to the rear of the
center notch, with all tilt ring backlash held lightly
to the rear.
Machines prior to gearless ti It continue to be adjusted
for ti It detent entry of .00211 - .004 11 to the rear.
10.20 WEAR COMPENSATOR - OVERCOMPENSATION/
ROLLER DROP
Overcompensation may be attributed to worn or
rounded edges on the bronze motor pu Iley teeth or to
worn pawls on machines equipped with nylon motor
pawls.
Slippage of the driving clutch pawls could relax the
selection system sufficiently to induce roller drop.
10.21 TYPEHEAD HOMING ON MACHINES WITHOUT
SHIFT OPERATION
In most cases it is not necessary to loosen the rotate
5-16
pulley for typehead homing on I/O Printers without
shift.
Homing may be accomplished easi Iy by adjusting the
shift arm screw, since these units do not uti lize shift
operation.
10.22 ANALYZING PRINT FAILURES
Some cases of Mal-Selection result in printing a 11.11
character which makes it difficult to determine the
ti It and rotate se lecti on .
The ti It and rotate selection may be easi Iy deter-
mined if a standard ET type element is substituted
temporari Iy to ana Iyze the fai lure. The standard ET
type elements print a different character for each
ti It and rotate se lection.
10.23 MAL-SELECTION AT +5 ROTATE
Occasional mal-selections at the plus five rotate
band on the typehead can be caused by:
1. Variations of cycle shaft speed. A sudden in-
crease in momentum of the cycle shaft may cause
the typehead to rotate beyond the plus five de-
tenting position. If the motor clutch pawl slips
off a tooth of the motor pulley during the begin-
ning of a plus five rotate operation, the cycle
shaft wi II slow up for an instant: when the pawl
re-engages in the next tooth of the motor pu Iley,
there wi" be a sudden surge felt throughout the
cyc Ie shaft system. This surge wi II cause over-
rotati on of the type head .
2. SELECTRIC I/O Printers operating in an open-
ended mode (1052/1053/1062) may also exper-
i ence th i s prob lem, due to the fact that they are
being pulsed at a constant rate of 14.89 char-
acters per second, whereas the printer is oper-
ating at a mechanical rate of 15.5 characters per
second. This difference in speed is a bui It-in
safety margin, but due to this difference in speed,
the cyc Ie clutch may try to latch up at the end
of a cycle and then be unlatched again by the
next incoming pulse. The cycle spring clutch
will be opened just far enough to allow the shaft
and clutch to slip slightly. When the cycle
spring starts driving again, the shaft wi II turn
with an increased momentum and the over-ro-
tating condition will result.
Several solutions to this problem wi II be listed be low:
1. The motor pulley has been redesigned as shown
in Figure 1 below. The engagement area on the
pulley for the motor pawl has been increased so
as to allev.iate the possibi lity of the pawl slip-
ping out of the tooth. All machines in the Field
shou Id be usi ng the motor pu lIey illustrated be low.
Old style motor pulleys are easily recognizable
since they wi II not have this flattened notch as
illustrated.