Chevrolet 1977 light duty truck, Service Manual

Page: 465 / 861

toward the inside o f cover an d drive it into position with
Tool J-23042 (fig. 6A-36).
CAUTIO N: Support cover at sealing area.
(Tool J-971 m ay be used as support.)
C A M S H A F T
Measuring Lobe Lift
N O T E : This procedure is sim ilar to that used for
checking valve timing. If im p ro p e r valve operation
is indicated, m easure the lift o f each push rod in
consecutive o rd er and record the readings.
1. Rem ove valve m echanism as outlined.
2. Position indicator with ball socket a d ap ter (Tool
J-8520) on push rod (fig. 6A-37).
3. Rotate the c ra n k sa h ft slowly in the direction o f
rotation until the lifter is on the heel o f the cam lobe. At
this point, the push rod will be in its lowest position.
4. Set dial indicator on zero, then rotate the
ca rn k s h a ft slowly, or attach an auxiliary starter switch
an d " b u m p " the engine over, until the push rod is in the
fully raised position.
CAUTIO N: Whenever the engine is cranked
remotely at the starter, with a special ju m p e r
cable or other means, the " BA T T ' positive lead
m ust be disconnected fr o m the coil.
5. C o m p are the total lift recorded from the dial
indicator with specifications.
6. C ontinue to rotate the crankshaft until the
indicator reads zero. This will be a check on the accuracy
o f the original indicator reading.
7. If cam sh aft readings for all lobes are within
specifications, remove dial indicator assembly.
8. Install and adjust valve m echanism as outlined.
Removal
1. Remove engine, following procedure on page
6A o f this section.
2. Remove lifters as previously outlined.
3. Remove crankcase front cover as previously
outlined.
4. Remove fuel pump.
5. Align tim ing gear marks then remove the two
cam sah ft thrust plate bolts by working through holes in
cam sh aft gear (fig. 6A-38).
6. Remove the cam shaft and g ear assembly by
pulling it out through the front o f the block.
NOTE: Support cam sh aft carefully w hen removing
so as not to d a m a g e the cam sh aft bearings.
Inspection
The cam shaft b earin g jo u rn als should be measured
with a m icrom eter for an out-of-round condition. If the
journals exceed .001" out-of-round, the cam sh aft should
be replaced.
The cam shaft should also be checked for alingment.
The best method is by use o f " V " blocks and a dial
indicator (fig. 6A-39). The dial indicator will indicate the
exact a m o u n t the c a m sh a ft is out o f true. If it is out
more than .0015" dial indicator reading, the cam shaft
should be replaced.
Inspect the ca m sh a ft gear and thrust plate for w ear
or damage. M easure the cam sh aft end play. This should
be .001" to .005" (fig. 6A-40).
Gear Replacement
1. If the inspection indicated that the camshaft,
gear or thrust plate should be replaced, the gear must be
T I M IN G
M A R K S
TH R U S T
PLATE
S C R E W S