IBM Selectric Reference Manual page 15

ESCAPEMENT
I. The carrier should escape smoothly and positively through-
out the full length of the writing line and through the right-
hand margin under spacebar operation and lobulation.
2. Check for frayed or loose transport cords.
3. Tension should be maintained on the right-hand transport
pulley to maintain its mounting parallel to the powerframe.
Its outside flanges should be 1-7/32" from the right-hand
outside surface of the power frame.
4. The I ine-gage holder must clear the platen at all points,
and not impede carrier motion.
5. A minimum of .015" clearance should exist between the
carrier-return shoe and the spring-clutch. Note, however,
that excessive clearance can result in erratic carrier-return
motion.
6. Check for 1/2-3/4 pounds of mainspring tension measured
at the carrier as it escapes through the linelock load at the
extreme ri ght-·hand margin.
7. Check for. 002" - .004" backlash of the tab governor and
carrier-return pinion gears with the escapement gear.
8. Letter escapement should occur as soon after print as pos-
sible.
9. The trigger guide should disengage the trigger from the
escapement-torque-bar arm when the escapement pawl
has cleared the rack by .010" - .015". Both the letter-
escapement and the spacebar operation should allow. 005"
- .010" excess motion after the trigger has disengaged the
trigger from the torque-bar arm.
10. When operated, the tab lever should overthrow the tab-
lever latch by .005" - .010" without being choked off by
the tab torque-bar lockout lug or backup eccentric, and
without overthrowing into the tab rack. Observe the opera-
tion at both ends and the middle of the torque bar. Dynam-
ically check for tab failures using five irregularly set tab
stops for at I east fi ve co I umns.
11. Check to make sure that the carrier-return operation un-
latches the tab when both operations occur simultaneously.
12. With the backspace operated manually, the escapement
pawl should just fail to get a new tooth on the escapement
rack.
13. There should be a clearance of .005" - .015" between the
front of the backspace pawl and a tooth of the backspace
rack (with the carrier at rest).
14. Overthrow clearance of .010" - .020" is required between
the interposer pawl s and the operational-latch bracket when
the operational cams are on their high point.
1-13
MOTOR DRIVE AND CARRIER RETURN
I. Check for adequate tension of the motor-pulley belt
I
or
for a frayed or noisy belt.
2. The selector and operational cam shafts, and the print and
filter shafts, must have .002" end play.
3. There must be freedom from binds in the idler gear train
with minimum backlash.
4. With the carrier-return cam on its high point, the carrier-
return arm should overthrow its keeper by .020" - .030".
5. The carrier-return brake shoe should cause the carrier-
return spring clutch to drive the carrier no later than when
the escapement pawl clears the last one-third of the es-
capement rack tooth. The clutch shoe should overlap the
last three coils of the spring clutch.
6. The carrier-return unlatching link must positively unlatch
the carrier-return latch at the left-hand margin with .005"
- .010" overtravel when the margin-rack overbank is set.
7. The escapement pawl must not drag the escapement rack
during carrier-return operations.
8. Measure one-half to one pound tension of the shock un-
loader at the left-hand margin whi Ie unlatching the carrier-
return keeper-latch arm.
INDEXING AND PAP ER FEED
1. Check for. 015" - .030" clearance between the platen
ratchet and the index pawl, at rest.
2. Index operation should result in one full-tooth motion of
the index pawl with respect to the platen ratchet (in single-
I inespace position) and two full-teeth motion with no evi-
dence of hesitation or drag (in the double-linespace posi-
tion) .
SHIFT
Check the cam and spring for rust. Check for the positive re-
lease of the ratchet when the key lever is two thirds down.
Turn power on, and hold the shift ratchet (grey section). Re-
lease the ratchet by pressing the key. Allow the ratchet to ro-
tate slowly while holding down on the key. The shift cam should
stop at a fully detented position for each 180
0
operation. The
white nylon roller should seat fully in cam notch.