Therm Ostat And W Ater O U Tle; Crankshaft And Bearings - Chevrolet 1988 Light Duty Truck Repair Manual

6A3-16 4.3 LITER V-6
• C o m p re ss the valve sp rin g using J 8062
(figure 20). Com press the spring enough so
the lower valve stem groove can be seen
clearly.
• Push a new O-ring seal (23) onto the valve
stem. The seal is to be installed on the stem 's
lower groove. Make sure the seal is flat and
not twisted.
• Apply a small am ount of grease to the area of
the upper valve stem groove. Assem ble the
two valve keepers using the grease to hold the
keys in place. Make sure the keepers seat
properly in the groove.
• Release the com pressor tool. Make sure the
valve keepers stay in place.
• Repeat the preceding steps on the rem aining
valves.
• Check each O-ring seal for leakage (figure 24).
• Place the suction cup su p p lied w ith
J 23738-A over the shield.
• Connect J 23738-A to the suction cup
and apply a vacuum. Watch the vacuum
pump gage. No air should be able to
leak past the seal. If the seal will not hold
a vacuum, it may have been dam aged or
im properly installed.
M easure
Valve spring installed height of each spring as
follows.
1. Use a narrow thin scale. A cutaway scale may
be helpful.
2. Measure from the top of the shim or the spring
to the top of the shield.
3. If this m easurem ent exceeds the figure given
in " S pecifications," install valve spring seat
shims approxim ately 1.6 mm (1 /ie-inch) thick
(betw een th e s p rin g and c y lin d e r head).
NEVER shim the spring so as to give an
installed height under the specified figure.
THERMOSTAT AND WATER
OUTLET
R em o ve or D is c o n n e c t
0
1. Bolts.
2. Water outlet.
3. Gasket.
4. Therm ostat.
L*
Inspect
Water outlet for cracks.
-► 4-
Install or C o n n e c t
1. Therm ostat.
2. New gasket.
3. W ater outlet.
4. Bolts.
T ig h te n
Bolts to 28 N m (21 ft. lbs.).

CRANKSHAFT AND BEARINGS

Clean
C rankshaft with solvent.
— Do not scratch the bearing journals.
— Blow all sludge from the oil passages with
compressed air.
• Main bearing inserts. W ipe free of oil with a
soft cloth.
Inspect
• C rankshaft for cracks. Use the m agnaflux method, if
available.
• C ra n k p in s , m ain b e a rin g jo u rn a ls and th ru s t
surfaces for scoring, nicks, or damage caused by
lack of lubrication.
• Main bearing inserts for scoring or other damage.
In general, the lower inserts (except the #1 bearing),
show greater wear and the most distress from fatigue. If,
upon inspection, the lower insert is suitable for use, it can
be assumed that the upper insert is also satisfactory. If
the lower insert shows evidence of wear or damage, both
the upper and lower inserts must be replaced.
M easu re
Main bearing and connecting rod journal diameters
(figure 25). Compare with " S pecifications." Grind or
replace the crankshaft if necessary.
Main bearing and connecting rod journals for taper
and out-of-round (figure 25). If the jo u rn a ls are
tapered more than 0.001-inch or out-of-round more
than 0.002-inch, grind or replace the crankshaft.
Crankshaft run-out.
• Mount the crankshaft in V-blocks or between
centers.
• Use a dial indicator.
• If the m ain jo u rn a ls are m is a lig n e d , the
crankshaft is bent and must be replaced,
along with the main bearing.