Chevrolet 10 Series 1970 Service Manual page 334

ENGINE 6-12
F ig . 2 2 —O il D e fle c to r C lip s In s ta lle d
2. Apply a test p ressu re o f 3 pounds higher than the
rad iator cap (fig . 21), i.e . 18 pounds fo r a 15 pound
cap.
3. If the p ressu re w ill not hold, there is eith er an
internal o r external leak in the system .
Cylinder Head Torque and V a lv e Adjustment
Retorquing the cylin d er head bolts is not n ecessary
unless a gasket has been rep laced ,or a leak is suspected.
V a lve lash must alw ays be adjusted a fte r the head has
been torqued.
B efo re adjusting the valve lash, it is e x trem ely im ­
portant that the engine
n orm a lize the expansion
be thoroughly warm ed up to
o f all parts. T h is is v e ry
im portant because during the w arm -up period, the valve
clearance w ill change considerably.
1. A fte r the engine has been n orm alized, rem ove ro ck er
arm co vers and gaskets.
CAUTIO N: Do not p ry ro ck er arm co ver loose.
Gaskets adhering to cylin d er head and ro ck er
arm co ver may be sheared by bumping end of
ro ck er arm co ver rea rw a rd with palm of hand or
a rubber m allet.
2. With the engine running
ro ck er arm nut until the va lve ro ck er arm starts
to clatter.
3. Turn rock er arm nut down slow ly until the clatter
just stops. T h is is the z e ro lash position.
NOTE: O il d eflecto r clip s a re
available (fig. 22).
4. Turn nut down 1/4 additional turn and pause
seconds until engine
ditional 1/4 turns, pausing 10 seconds each tim e,
until nut has been turned down 1 full turn from
the ze ro lash position.
NOTE: This 1 turn preload adjustment must be
done slow ly to allow the lift e r to adjust its e lf to
prevent the p o ssib ility o f in terferen ce, between
the inlet va lve head and top o f piston, which
might resu lt in internal damage and/or bent push
rods. N oisy lifte r s should be replaced.
5. Repeat Steps 2, 3 and 4 to adjust the re s t o f the
va lves.
6. Clean gasket surfaces on cylin d er heads and ro ck er
arm co v e rs with d egrea ser then install rock er arm
co vers, using new gaskets,
specifications.
at id le, back o ff va lve
co m m ercia lly
runs sm oothly. Repeat ad­
and torque bolts to
CHEVROLET TRUCK SERVICE MANUAL
10