Chevrolet 70 1969 Series, Shop Manual

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POWER BRAKE 5-50
INSPECTION
CYLINDER HEAD
Inspect cylinder head for cracks or breaks. Replace
with new head if cracked or dam aged.
INLET AND DISCHARGE
VALVE SPRINGS
Discard used inlet and discharge valve springs and re­
place with new springs.
INLET AND DISCHARGE
VALVES AND SEATS
Inspect inlet and discharge valves and seats for signs of
excessive wear. Replace valves if grooved deeper than
0.003 inches at point of seat contact. Replace valve seats
if condition is such that seats can no longer be refaced.
UNLOADING PISTONS
AND PLUNGERS
Inspect pistons, plungers, and plunger guides for signs
of dam age or excessive wear. New unloading pistons
should slide easily in bores. Replace O-rings in unloader
piston. Check unloading piston return spring dimension
and com pare with “ Specifications” listed at end of this
m anual. Replace spring if necessary.
CRAN KCASE AND END COVERS
C heck crankcase and end covers for cracks or other
dam age. Replace with new parts if dam aged.
CRANKCASE BEARING BORE
Check the fit of ball bearing in the com pressor
crankcase bearing bore. The bearing should require a fin­
ger press fit. It is recom m ended to replace com pressor
crankcase if bore is worn or dam aged.
CYLINDER BLOCK (Fig. 9)
Use telescoping gauge to check cylinder bores for out-
of-rounri and taper. Bores which are scored or out-
of-round more than 0.002 inches, or tapered m ore than
0.003 inches m ust be rebored, honed, or ground oversize.
Pistons and rings 0.010 inches, 0.020 inches, and 0.030
inches oversize are available. Cylinder bores m ust be
sm ooth, straight, and round and m ust be finished with a
500 (or finer) grit hone. The clearance between piston and
cylinder wall on models using cast iron pistons m ust not
be less than 0.002 inches or m ore than 0.004 inches.
Cylinders m ust be cleaned thoroughly after honing or
boring operation. Even slight traces of abrasive m aterial
left on the cylinder walls m ay cause rapid ring and wall
wear and early com pressor failure. W ipe down the cylin-
Figure 9— Measuring Cylinder Bore Diameter
der walls with very fine crocus cloth. This loosens em bed­
ded abrasive m aterial and also knocks off foreign m aterial
left by the honing stones; then use a stiff brush and hot,
soapy water to wash down the walls. It is absolutely es­
sential for a good job, to clean the cylinder walls of all
abrasive m aterial, since such m aterial will cause rapid
wear of pistons and rings. A fter cleaning the cylinder
walls, wash the walls with a cloth and light engine oil,
wiping the oil off with a clean, dry cloth. R epeat this until
the clean, dry cloth is free of all visible dirt.
PISTONS (Fig. 10)
Exam ine pistons for scoring, cracks, or dam ag e of any
kind. M easure outside diam eter of piston with a m icrom e­
ter and com pare this m easurem ent with the inside diam e­
ter of cylinder bore. C learance should not be less than
0.002 inches or m ore than 0.004 inches. Piston over 0.004
inches smaller than cylinder bore m ust be replaced with
an oversize piston.
NOTE: When measuring the outside diameter
of the piston, make sure that the micrometer is
at a 90 degree angle to the piston pin bore.
This will enable correct measurement.
PISTON PINS AND BUSHINGS
C heck fit of piston pins in pistons and connecting rods.
Pins must be light press fit in pistons. If piston pin is
loose in piston, the pin. piston, or both m ust be replaced.
Check fit of piston pins in connecting rod bushings by
rocking pins in bushings. If looseness is evident, replace
connecting rod bushings as directed under "C o m pressor
R epair.” Discard all piston pin lock wires.
PISTON RINGS (Figs. 11, 12, and 13)
Check fit of piston rings in ring grooves, and
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK SHO P M A N U A L