GMC 4000 Series Service Manual page 286

7 W JK - ' /
1 End Bracket
2 Adjusting Screw
3 Push Rod
4 Rocker Arm Shaft Bracket
5 Intake Manifold
removal of valve lifters is desired, a special tool
is available to remove lifters without removing
cylinder head. Insert tool through push rod holes
in cylinder head and into lifter. Turn knob at upper
end of tool to lock the tool into lifter, then pull
lifter out of bore.
NOTE: Valve lifters should be installed in
bores from which they were removed.
INSTALLATION
1. If valve lifters have been removed from
305 or 351C engines lubricate lifters with special
break-in compound, and use special tool to insert
lifters into respective bores.
2. Place push rods in original positions, then
place rocker arm shaft and bracket assembly (fig.
31) on cylinder head, being careful to engage rocker
arm screw s with sockets in push rods. Tighten
bracket bolts to 20 to 25 foot-pounds torque.
3. Check clearance between rocker arm end
brackets and adjacent rocker arm. If a clearance
of approximately 0.030 inch does not exist, loosen
end bracket bolts and relocate brackets as allowed
by clearance in bracket hole, then tighten bolts to
specified torque.
4. Make initial adjustment to provide clear­
ance of 0.014 inch at intake valves, and 0.022 inch
at exhaust valves.
5. Lubricate rocker arms with engine oil.
6. Install rocker arm covers temporarily while
engine is run to warm up to operating temperature.
With engine idling and temperature at 160 degrees,
G M C S E R V I C E M A N U A L
C rankcase Ventilation V a lv e
6 Rocker Arm Shaft
7 Spring
8 Bracket Bolt
9 Flat Washer
Figure 31 — Valve Rocker Arm s and Shaft Installed
10 Exhaust Manifold
11 Exhaust Manifold Bolt Lock
12 Rocker Arm
13 Special Bolt
adjust intake valves to 0.012 inch and exhaust valves
to 0.018 inch.
NOTE: Inspect crankcase ventilation valve
(fig. 31) and clean or replace as necessary.
7. Install rocker arm cover using new cover
gasket.
VALVE SPRING REPLACEMENT
(CYLINDER HEAD INSTALLED)
In most vehicles it is possible to replace a
broken valve spring without removing cylinder
head by following the procedure outlined below:
When it is necessary to replace a valve spring
and/or seals on valve stem s, the special tools
shown in figure 32 may be used to facilitate the
operation without removing the cylinder head. Pro­
ceed in following manner to replace valve spring
and retaining parts:
1. Remove valve rocker arm cover.
2. Remove spark plug from cylinder on which
work is to be done. Use spark plug gasket and in­
stall adapter (J-21546) in sparkplug hole.
3. Remove rocker arm shaft and bracket a s­
sembly from cylinder head. Install a 3/8-16 stud
in bracket bolt hole adjacent to the valve spring to
be removed. Stud must have sufficient threads to
permit screwing stud nut down one-half inch after
compressor contacts valve spring cap.
4. Turn engine crankshaft to place piston at
Sec. 6A
Page 275
GASOLINE ENGINES
FRONT
T-5602