Measuring Main Bearing Clearance - GMC T Series 1994 Repair Manual

7.4L engines:
— J 7049-1: 0.08 mm (0.003 inch) oversize.
— J 7049-2: 0.38 mm (0.015 inch) oversize.
— J 7049-3: 0.76 mm (0.030 inch) oversize.
— These reamers also available in Reamer Set
J 7049.

MEASURING MAIN BEARING CLEARANCE

Main bearings are of the precision insert type and do
not use shims for adjustment. If clearances are found to
be excessive, new upper and lower inserts will be
required.
The simplest, most accurate way to measure main
bearing clearance is with the use of gaging plastic. This
wax-like material compresses evenly between the bear­
ing and journal surfaces without damaging them. Pro­
ceed as follows:
Clean
All oil from the crankshaft journal and main bearing
inserts.
Install or Connect (Figure 26)
• Refer to the proper section for additional informa­
tion.
1. Main bearing inserts and crankshaft, as outlined in
the proper section.
2. Gaging plastic.
A. Begin with the rear main bearing.
B. Wipe the oil from the crankshaft journal and the
lower main bearing insert.
C. Place a piece of gaging plastic the full width of
the lower bearing insert (parallel to the crank­
shaft) on the journal (figure 26). Do not rotate
the crankshaft w hile the gaging plastic is
between the bearing and journal.
ASSEMBLY
Assemble
*
Valves and components. Refer to the proper sec­
tion.
3. Main bearing cap and bolts.
NOTICE: Refer to "Notice" on page 6A-1.
Tighten
&
Bolts to " Specifications."
Remove or Disconnect
• Main bearing cap.
DO NOT REMOVE THE GAGING PLASTIC FROM
THE JOURNAL OR LOWER MAIN BEARING INSERT.
m
Measure (Figure 27)
• Gaging plastic as follows:
1. The flattened gaging plastic will be found adhering
to either the lower bearing insert or journal.
2. On the edge of the gaging plastic envelope there is
a graduated scale. Without removing the gaging
plastic, measure its compressed width (at the wid­
est point) with the graduations on the gaging
plastic envelope (figure 27).
3. If the flattened gaging plastic tapers toward the
middle or ends, there is a difference in clearance
indicating taper, low spot, or other irregularity of the
bearing or journal. Make sure to measure the jour­
nal with a micrometer if the flattened gaging plastic
indicates more than 0.001-inch (0.0005-inch on
2.2L engines) difference.