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8-8
TESnNG
CAMSHAFT
LOBE UFT
Check the lift of each lobe in
consecutive order and make a note
of the readings.
1. Remove the air cleaner and
the valve rocker
arm
cover(s).
2. On a six-cylinder engine, re-
move the valve rocker arm shaft
assembly.
On a V -8 engine, remove the
rocker arm stud, or stud nut, fulcrum
seat and rocker arm. Use the adapter
for ball-end push rods (Fig. 3).
3. Make sure the push rod is in
the valve lifter socket. Install a dial
indicator in such a manner as to
have the ball socket adapter of the
indicator on the end of the push
rod and
in
the same plane as the
push rod movement (Fig. 2 or
3).
On a socket-type push rod, posi-
tion the actuating point of the indi·
cator in the push rod socket and in
the same plane as the push rod
movement (Fig.
2).
4. Disconnect the brown/red lead
(I
terminal) and the red and blue
lead
(S
terminal) at the starter
relay. Install an auxiliary starter
switch between the battery and S
terminals of the starter relay. Crank
the engine with the Ignition switch
OFF.
"Bump" the crankshaft over until
the tappet or lifter is on the base
circle of the camshaft lobe. At this
point, the push rod will be
In
its
lowest position,
OF PUSH ROO
SOCKET
FIG. 2-Camshaft lobe lift-
Six Cylinder Engines
GROUP
8-ENGINE
5. Zero the dial indicator. Con-
tinue to rotate the crankshaft slowly
until the push rod is in the fully
raised position.
6. Compare the total lift re-
corded on the indicator with speci-
fications.
7. To check the accuracy of the
original indicator reading, continue
to rotate the crankshaft until the
indicator reads zero.
H
the Uft on
any lobe is below specified wear
Umits, the camshaft and the valve
Ufters operating on the worn lobe(s)
must be replaced.
NOTE
Comparing the size of one cam-
shaft lobe to another, with a micro-
meter or other measuring instrument,
is not a satisfactory method of check-
ing camshaft lobe lift, owing to
tolerances on base circle radii.
8.
On a six-cylinder engine, install
the rocker arm shaft assemblies.
On a V -8 engine, install the rocker
arm, fulcrum seat and
stud.
Adjust the valve clearance (Page
8-11
)
9. Install the valve rocker arm
cover(s) and the air cleaner.
COMPRESSION TEST
Dynamic Compression Test. To
perform a dynamic compression
check, follow the procedures in
Part 9-1, Section 1 under Ignition
System Tests-
Compression Gauge Check
1. Be sure the crankcase oil is at the
proper level. DISCONNECT AL-
TERNATOR. Connect a high speed
battery charger to battery to ensure
cranking speed does not vary bet-
ween cylinders. Operate the engine
for a minimum of 30 minutes at
FIG. 3-Camshaft lobe ltft-
V-8 Engines -Typical
1,200
r.p.m. or until the engine is
at normal operating temperature.
Remove the spark plugs.
2. Disconnect the brown/red lead
(I terminal) and the red and blue lead
(S terminal) at the starter relay. In-
stall an auxiliary starter switch be-
tween the battery and S terminals of
the starter relay. Check valve clear-
ances as indicated in Group 8, Sec-
tion 2, using the auxiliary starter
switch to turn engine. Crank the
engine with the ignition switch
off.
3.
Set the throttle plates and
choke plate in the wide open position.
4. Install a compression gauge in
No. 1 cylinder.
5. Using
the
auxiliary
starter
switch, crank the engine a minimum
of five pumping strokes, and record
the highest gauge reading.
Note the number of compression
strokes required to obtain the high-
est reading.
6.
Repeat the test on each cylin-
der, cranking the engine the same
number of times for each cylinder
as was required to obtain the highest
reading on the No. 1 cylinder.
Test Conclusions. The test pres-
sures should fall within the band
specified and the compression of all
cylinders should be uniform within
20 psi.
If one or more cylinders exhibit
compression figures lower than that
specified, re-run the engine at
1200
rpm for 5 minutes. Recheck the low
reading cylinders to confirm the
original results.
A reading of more than the allow-
able tolerance above normal indi-
cates excessive deposits in the cyl-
inder or wrong cylinder head(s) on
the engine.
A reading of more than the allow-
able tolerance below normal indi-
cates leakage at the cylinder head
gasket, piston rings or valves or
wrong cylinder head(s) on the en-
gine.
A low, even compression in two
adjacent cylinders indicates a cylin-
der head gasket
leak.
This should be
checked
before
condemning
the
rings or valves.
During a compression test, if the
pressure fails to climb steadily and
remains the same during .the first
two successive strokes, but climbs
higher on the succeeding strokes, or
fails to climb during the entire test,
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