GMC T Series 1994 Repair Manual page 544

B. Main bearing and connecting rod journals for taper
and out-of-round (figure 59). If the journals are
tapered or out-of-round more than 0.025 mm
(0.001-inch), replace the crankshaft.
C. Crankshaft runout (figure 60).
• Mount the crankshaft in V-blocks or between
centers.
• Use a dial indicator as shown.
• If runout exceeds 0.01 mm (0.0004 inches), the
crankshaft is bent and must be replaced, along
with the main bearings.
AVAILABLE BEARING SIZES
Factory Main Bearing Selection
There are five main bearings numbered 1 through 5
from the front of the engine. There is an arrow on the
bearing cap that points toward the front of the engine.
The center number 3 bearing is the thrust bearing. The
upper bearing halves have an oil groove. The lower
bearing halves do not have an oil groove.
During factory assem bly the main bearings are
select-fitted to each of the five main bearing bores. The
proper size code is stamped on the pan rail at the
corresponding main bearing bulk head. The total diame­
ter size range of the main bearing bores 1 through 5 is
79.826 mm to 79.850 mm. This range is divided into
three sizes and stamped #1, #2, or #3 on the pan rail.
The crankshaft is color marked red, blue, orange, or
white near the main bearing journal. The proper bearing
selection is made by using the number on the pan rail.
Color marking on the corresponding crankshaft jour­
nal for selecting the proper bearing halves are shown in
the crankshaft main bearing specifications at the rear of
this section.
Main Bearing Selection for Service
• Main bearings are available in Standard, 0.013-mm
(0.0005-inch) and 0.026-mm (0.001-inch) under­
sizes for select fitting to attain proper main bearing
clearance. "Undersize" refers to the crankshaft
diameter."
• For service purposes, bearing size combinations
that provide the following clearance, as measured
with the plastigage procedure.
A. Main Bearing #1, #2, #3, and #4: 0.045 to 0.083
mm (0.0018 to 0.0033 inches).
B. Main Bearing #5: 0.055 to 0.093 mm (0.0022 to
0.0037 inches).
Connecting Rod Bearing Selection
• Connecting rod bearings are available in 0.026 mm
(0.001-inch) undersizes for select fitting.
• Turbocharged and naturally aspirated light duty
emissions engines may have both standard and
0.08-mm (0.003-inch) OVERSIZE connecting
rod bearings. The oversize connecting rods are
stamped "O.S." on the cap's lower end.
FLYWHEEL
IJS Ji Clean
M ating su rfa ce s of cra n ksh a ft and flyw h ee l.
Remove any burrs.