Assembly Of The Engine; Prior To Assembly; Crankshaft And Main Bearing Installation; Inspecting Crankshaft End Play - GMC T Series 1994 Repair Manual

• Main bearing and connecting rod journals for taper
and out-of-round.
• Maximum journal taper is 0.001 inch.
• Maximum out-of-round is 0.002 inch.
• Crankshaft run-out.
A. Mount the crankshaft in V-blocks or between
centers.
B. Use a dial indicator.
C. If the main journals are misaligned, the crank­
shaft is bent and must be replaced. The main
bearings must also be replaced at the same
time.
D. Grind or replace the crankshaft if necessary.

PRIOR TO ASSEMBLY

The importance of cleanliness during the assembly
procedure cannot be overstressed. Dirt will cause pre­
mature wear of the rebuilt engine.
Lubricate all moving parts lightly with engine oil or
engine assembly lubricant (unless otherwise specified)
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 exces­
sive, both upper and lower bearing 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.

INSPECTING CRANKSHAFT END PLAY

++
Install or Connect
NOTICE: For steps 4 and 6, refer to "Notice"
on page 6A3-1.

ASSEMBLY OF THE ENGINE

A. Micrometer
Figure 36— Measuring the Crankshaft Journals
Important
• If any undersized bearings are used, they must
be fitted to the proper journals.
2. Crankshaft.
3. Lower main bearing inserts to the main bearing
caps.
Measure
• Main bearing clearance. Refer to SECTION 6A.
• Apply engine oil to the main bearing inserts.
4. Main bearing caps (except rear cap) and bolts to
the block.
• Main bearing cap bolts (except rear cap) to 100
N-m (75 lbs. ft.).
5. Rear main bearing cap.
6. Rear main bearing cap bolts.
Tighten
$
• Rear main bearing cap bolts to 14 N-m (124
lbs. in.).
Measure
Crankshaft end play, as follows:
— Firmly thrust the crankshaft first rearward then
forward. This will line up the rear main bearing
and crankshaft thrust surfaces.
Tighten
V0573