Assembly Of Engine; Prior To Assembly; Crankshaft And Main Bearing Installation; Rear Crankshaft Oil Seal Retainer Installation - GMC 1990 Light Truck Repair Manual

PRIOR TO ASSEMBLY

The importance of cleanliness during the assembly
procedure cannot be overstressed. Dirt will cause
premature wear of the rebuilt engine.
Lubricate all moving parts lightly with engine oil or
engine assembly lubricant (unless specified otherwise)
during assembly. This will provide initial lubrication when
the engine is started.
CRANKSHAFT AND MAIN
BEARING INSTALLATION
Main bearings are of the precision insert type and do
not use shims for adjustment. If clearances are excessive,
a new bearing plus both upper and lower inserts will be
required. Service bearings are available in standard size
and 0.001-inch, 0.002-inch, 0.009-inch, 0.010-inch, and
0.020-inch undersize.
Selective fitting of both rod and main bearing inserts is
necessary in production to obtain close tolerances. For
this reason you may find one half of a standard insert with
one half of a 0.001-inch undersize insert which will
decrease the clearance 0.0005-inch from using a full
standard bearing.
Some engines may have rear main bearings that are
0.008-inch wider than standard across the thrust faces.
• The crankshaft on these engines can be identified
by " .008" stamped on the rear counterweight.
• If the rear main bearings are replaced, they must
have the proper distance between thrust faces to
obtain proper crankshaft end play.
■n- Install or Connect
1. Upper main bearing inserts to the block.
Important
• If any undersized bearings are used, make
sure they are fitted to the proper journals.
2. Crankshaft.
3. Lower main bearing inserts to the main bearing
caps.
Measure
m
• Main bearing clearance. Refer to GENERAL
ENGINE MECHANICAL (SEC. 6A).
• Apply engine oil to the main bearing inserts.
4. Main bearing caps (except rear cap) and bolts to the
block.
Tighten
• Main bearing cap bolts to 100 N m (75 ft. lbs.).
5. Rear main bearing cap.
• Apply engine oil to the bearing inserts.
6. Rear main bearing cap bolts.
Tighten
• Bolts to 14 N-m (10 ft. lbs.).

ASSEMBLY OF ENGINE

4.3 LITER V-6 6A3-17
Measure
Crankshaft end play, as follows:
• Tap the end of the crankshaft first rearward
then forward with a lead hammer. This will line
up the rear main bearing and crankshaft thrust
surfaces.
• Tighten the rear main bearing cap bolts to 110
N-m (80 ft. lbs.).
• With the crankshaft forced forward, measure
at the front end of the rear main bearing with a
feeler gage (figure 26). The proper clearance
is 0.002-0.006-inch.
• If correct end play cannot be obtained, be
certain that the correct size rear main bearing
has been installed. Production engines may
have rear main bearings that are 0.008-inch
wider across the thrust faces than standard.
L 9
Inspect
• Crankshaft for binding. Try turning the crankshaft to
check for binding. If the crankshaft does not turn
freely, loosen the main bearing cap bolts, one pair at
a time, until the tight bearing is located. Burrs on the
bearing cap, foreign matter between the insert and
the block or the bearing cap, or a faulty insert could
cause a lack of clearance at the bearing.
REAR CRANKSHAFT OIL SEAL
RETAINER INSTALLATION
IQ* Clean
• Gasket surfaces on the block and seal retainer,
-n - Install or Connect (Figure 27)
1. New gasket (84) to the block.
• It is not necessary to use sealant to hold the
gasket in place.