Thermostat And Water Outlet; Crankshaft And Bearings - GMC 1990 Light Truck Repair Manual

6A3-16 4.3 LITER V-6
• Compress the valve spring using J 8062
(figure 20). Compress 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 amount of grease to the area of
the upper valve stem groove. Assemble the
two valve keepers using the grease to hold the
keys in place. Make sure the keepers seat
properly in the groove.
• Release the compressor tool. Make sure the
valve keepers stay in place.
• Repeat the preceding steps on the remaining
valves.
• Check each O-ring seal for leakage (figure 24).
• Place the suction cup supplied with
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 damaged or
improperly installed.
Measure
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 measurement exceeds the figure given
in " Specifications," install valve spring seat
shims approximately 1.6 mm (1 /ie-inch) thick
(between the spring and cylinder head).
NEVER shim the spring so as to give an
installed height under the specified figure.
THERMOSTAT AND WATER
OUTLET
Remove or D isconnect
0
1. Bolts.
2. Water outlet.
3. Gasket.
4. Thermostat.
Inspect
I?
Water outlet for cracks,
install or Connect
+ 4-
1. Thermostat.
2. New gasket.
3. Water outlet.
4. Bolts.
Tighten
I^ l
• Bolts to 28 N-m (21 ft. lbs.).
Figure 25—Measuring the Crankshaft Journals

CRANKSHAFT AND BEARINGS

I J i Clean
• Crankshaft with solvent.
— Do not scratch the bearing journals.
— Blow all sludge from the oil passages with
compressed air.
• Main bearing inserts. Wipe free of oil with a
soft cloth.
Inspect
• Crankshaft for cracks. Use the magnaflux method, if
available.
• Crankpins, main bearing journals and thrust
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.
Measure
Main bearing and connecting rod journal diameters
(figure 25). Compare with " Specifications." Grind or
replace the crankshaft if necessary.
Main bearing and connecting rod journals for taper
and out-of-round (figure 25). If the journals 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 main journals are misaligned, the
crankshaft is bent and must be replaced,
along with the main bearing.