Chevrolet 70 Series 1970, Service Manual

Page: 270 / 841

REAR SUSPENSION 4-57
0 .1 0 0 . fo r each revolution of in d icato r needle, then
p ro c eed with valve le v e r gap adjustm en ts following:
AIR INTAKE AND EXHAUST
VALVE LEVER ADJUSTMENTS
IMPORTANT: B efo re making th ese ad ju st­
m ents the o v e rtra v e l le v e r m ust be ce n te re d a s
explained p reviously.
Two m ethods of adjustm ent a r e available:
1. Using Both A ir P r e s s u r e and Vacuum
NOTE: If vacuum so u rc e is av ailable, th is
m ethod w ill take le s s tim e to p e rfo rm adjustm ent.
Vacuum so u rc e is u sed to make the exhaust valve
le v e r gap check only.
2. Using A ir P r e s s u r e Only
NOTE: When th is method is used, it w ill take
longer to p e rfo rm adjustm en ts a s the valve cover
m ust be in p lace each tim e a ir p r e s s u r e is applied
and then rem oved to p e rm it adjustm ent of exhaust
valve le v e r.
In stru c tio n s covering le v e r adju stm ents a r e
identical fo r fro n t and r e a r valves. R e a r valve
le v e r and front valve le v e r m ust be bent to p ro p ­
e r settin g . In th e se valves both exhaust and intake
le v e rs a r e p a r t of one unit which contains " sc o re "
m a rk s to p e rm it easy bending. M echanics may a c ­
com plish th is o p eratio n with le v e r in the valve
body, o r le v e r may be rem oved and bent on the
bench.
METHOD USING AIR PRESSURE AND VACUUM
1. If a i r supply and vacuum lin es w e re not
connected to valve assem bly a s d ire c ted p rev io u sly
when centering valve o v e rtra v e l le v e r, connect
lin es.
2. Apply a i r p r e s s u r e and re g u late it to 80 to
110 p si. Apply vacuum and regu late it at ap prox­
im ately 15 inches.
3. Move o v e rtra v e l le v e r fo re and aft se v e ra l
tim e s and then back to tru e ce n te r position.
4. S tarting at tru e ce n te r position, slowly
move le v e r to w here a i r intake valve ju st begins
to open. L isten fo r escaping a ir . Note reading on
dial at th is point. Reading should be 0.025" to
0.027" fro m le v e r ce n te r position. If n e c e ssa ry ,
bend intake valve le v e r to c o rre c t setting (fig. 11).
5. R eturn o v e rtra v e l le v e r to ce n te r position.
Slowly move le v e r to exhaust side and at sam e
tim e note the vacuum gauge reading. When vacuum
ju st begins to fa ll off, the exhaust valve h as open­
ed. Valve should open when o v e rtra v e l le v e r is
moved 0.035" to 0.037" from ce n te r p osition. If
n e c e ss a ry , bend exhaust valve le v e r to c o rre c t
settin g (fig. 11).
Figure 10—Locating Valve Overtravel Lever Center Position
Figure 11 —Adjusting Air Valve Lever Gap
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL