Chevrolet 70 1969 Series, Shop Manual

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POWER BRAKE 5-36
Figure 7 — C h e c k in g C le a ra n c e U s in g P la st ig a g e
2. Check fit of piston pins in pistons and connecting rod
bushings. Pin m ust be light tap fit in piston and in
bushing. Determ ine which part is worn and replace as
necessary. To replace bushing in connecting rod, press
old bushing out and press new bushing into place.
3. Check fit of com pression and oil rings in ring grooves
in pistons. Clearances between ring and ring groove
m ust not exceed limits given in “ Specifications” at
end of this m anual. Place each ring in cylinder bore
and m easure ring gap. G ap must be within limits list­
ed in “ Specifications” at end of this m anual. If clear­
ances are not within these limits, new rings m ust be
used at assembly.
4. Exam ine connecting rod bearing inserts for scoring,
pitting, or visible wear. If dam age is evident, new in­
serts m ust be installed.
5. Checking C learance by Plastigage M eth o d :
a. To check fit of bearings on crankshaft install
bearing inserts into connecting rod. Clean the
crankshaft journals and the inserts so that all
oil is removed. “ Plastigage" is soluble in oil.
therefore oil will affect the accuracy of the read­
ing. “ Plastigage” is placed on the lower half of
the bearings as show n in Figure 7.
IMPORTANT: To check the clearance properly
using "Plastigage" it is essential not to move
the connecting rod or crankshaft when tight­
ening or loosening nuts.
b. Install connecting rod cap and tighten connecting
bolt nuts to 8 to 10 foot-pounds torque. This
should flatten “ Plastigage" to 0.002 inch. Check
m easurem ent on “ Plastigage” scale. If “ Plasti­
gage'' reading is under or exceeds 0.002 inch,
then inserts m ust be replaced. Check clearance
between side of connecting rod and cap and
cheek on crankshaft (fig. 8). If clearance exceeds
0.006 inch, new rods and caps must be used.
NOTE: DO NOT file or lap bearing caps or rods
to take up clearance; always use new bearing
inserts if clearances are excessive.
Figure 8 — C h e c k in g Rod a n d C a p to C r a n k s h a ft C le a ra n c e
CYLINDER BLOCK
1. Exam ine inside of cylinder bores for scoring or pit­
ting. C heck bores for out-of-round and taper. If out-
of-round m ore than 0.002 inch from top to bottom of
bore, replace with new cylinder block.
2. Exam ine studs in top of cylinder block. Replace bent
studs or studs having dam aged threads. W hen install­
ing new stud, m ake certain th a t replacem ent stud is
the sam e length as stud removed.
3. Exam ine cylinder block for cracks or broken cooling
fins. Replace block if dam aged in any way.
CRANKSHAFT AND BEARINGS
1. A bent or twisted crankshaft cannot be repaired. If
connecting rod journals are scored beyond repair or
worn more than limits listed in “ Specifications,” re­
place with new crankshaft.
2. Threads, keyway, and all ground and m achined sur­
faces m ust not be m utilated or worn.
3. Exam ine ball bearing for worn or dam aged balls; ro-
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK SHO P M A N UA L