Chapter A: General Diagnosis
18
Selective Length Pushrods
A few older engines with non-adjustable valve gear use
zero-lash hydraulic lifters. However, to allow for valve
train wear, the plunger of the lifter must be centered in-
side the body. This is accomplished by installing short-
er or longer pushrods. To check and adjust clearance:
1. Position the cylinder at TDC on its firing stroke.
2. Tigten the rocker arm locknut to the torque value
specified by the manufacturer.
3. Depress the pushrod end of the rocker arm with a
tappet bleed down wrench, a large screwdriver, or
other suitable tool to bottom the plunger in the
lifter.
4. Hold the end of the rocker arm down, and measure
the clearance between the valve stem tip and the
rocker.
5. Compare this value to the specification range for
that engine. If the clearance is too great, install a
longer pushrod. If it is too little, install a shorter
pushrod.
Pushrods for most engines are available in three sizes:
standard, 0.060 inch (1.5 mm) oversize, and 0.060 inch
(1.5 mm) undersize. In general, pushrods need to be
changed only after the head and block mating surfaces
have been resurfaced, or the valve seats have been re-
placed or excessively machined.
Setting Adjustable Rocker Arms
To set adjustable rocker arms with the engine not run-
ning, follow this procedure:
1. Position a cylinder at TDC on its power stroke so
both valves are closed.
2. Slowly tighten the rocker arm locknut to remove all
the slack from the valve train without compressing
the hydraulic lifter. The pushrod will no longer ro-
tate freely and the rocker can no longer wiggle from
side to side, figure 1-18.
3. Slowly tighten the rocker arm locknut an additional
three-quarters to one-and-one-half turns to posi-
tion the plunger in the center of its travel inside the
lifter. How much additional tightening is required
varies by engine. Check the Service Manual for
exact specifications.
Adjusting Clearance on Overhead
Camshaft Engines
Once the valve cover is removed on an overhead cam
(OHC) engine, the camshaft contacting the lifter is visi-
ble. Rotate the engine by hand while watching the
camshaft lobes to bring the cylinder to be adjusted into
position. Position the camshaft so that the base circle of
a cam lobe is directly in line with its follower or rocker
arm pad. Then, that valve is closed and a feeler gauge
blade can be inserted to check the clearance. If the en-
gine uses a screw-type adjuster, simply loosen the lock-
nut and reposition the screw until there is a slight drag
on the feeler gauge, figure 1-19. Tighten the locknut,
recheck clearance, and move on to the next valve. Con-
tinue until all the valves are set.
Setting Valve Lash with Replaceable Shims
The replaceable adjustment shims on most engines are
located between the camshaft lobe and cam follower. A
special tool is used to depress the follower so the shim
can be removed, figure 1-20. To adjust the valve clear-
ance, follow this general procedure:
Fig. 1-18.
Typical adjustable rocker arm service.
ADJUSTING
SCREW
LOCKNUT
VALVE
SPRING
EXHAUST
VALVE
ROCKER
ARM
ROCKER
SHAFT
CAMSHAFT
INTAKE
VALVE
Fig. 1-19.
Overhead cam engine with rocker arms and screw-type
adjusters.
Summary of Contents for ASE-A8
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