Chapter A: General Diagnosis
19
1. Position the cylinder to be checked at TDC.
2. Measure the clearance with a feeler gauge.
3. Compress the follower and hold it down using the
special tool.
4. Pry the shim loose with a small screwdriver, or other
suitable tool, and remove it with a magnet or pliers.
5. Measure the thickness of the shim with an outside
micrometer.
6. Calculate the thickness of the shim to be installed:
•Subtract the midpoint of the specified clearance
range from the measured clearance
•Add the result to the thickness of the shim that
was removed from the engine
•The result equals the thickness of the new shim
to be installed
7. Install the new shim in the recess in the top of the
lifter and firmly seat it into place.
8. Release the follower and recheck the valve lash
clearance.
Some engines use a smaller shim that fits directly on top
of the valve stem underneath the cam follower. To re-
place this type of shim, the camshaft and the follower
must be removed.
CAMSHAFT AND VALVE TIMING
Camshaft timing can be verified by removing the timing
cover and inspecting the timing marks, figure 1-21, or
by using a degree wheel and dial indicator. Incorrect
valve timing generally results from component wear.
Disassemble the camshaft drive, inspect all compo-
nents, and replace all worn or damaged parts with new
ones. Make sure both the crankshaft and camshaft re-
main in the TDC position and all timing marks are
aligned during assembly. Once the camshaft drive is in
place, follow the Service Manual procedures for rotating
the engine and verifying the alignment of the timing
marks. Once you have verified that all timing marks are
again in alignment and that the chain or belt is properly
tensioned, install the timing cover.
Under normal conditions, the initial valve timing of the
engine does not change. However, high-mileage opera-
tion can cause both timing chains and belts to stretch
or tensioners to weaken to the point where valve timing
is altered, figure 1-22. Excess slack in the drive assem-
bly causes the camshaft sprocket to lag behind the
crankshaft sprocket as the engine runs. The result is re-
tarded valve timing that can cause a lack of power at
higher engine speeds and loads. Symptoms are the
same as those caused by retarded ignition timing or a
lack of timing advance.
Variable Valve Timing
• Intake camshaft timing is continuously variable
using a hydraulic actuator attached to the end of
each intake camshaft. Engine oil flow to each hy-
draulic actuator is controlled by a camshaft position
SPROCKET
TIMING MARK
CAMSHAFT
SPROCKET
CRANKSHAFT
SPROCKET
ENGINE CASE
TIMING MARK
SPROCKET
TIMING MARK
CYLINDER HEAD
TIMING MARK
Fig. 1-21.
Typical timing belt arrangement for OHC engine.
SPECIAL
TOOL
ADJUSTING
SHIM
MAGNET
Fig. 1-20.
Depress the follower with the special tool to remove/install
the adjuster shim.
Summary of Contents for ASE-A8
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