Chevrolet 1991 Light Duty Truck Repair Manual page 356

6A-20 GENERAL ENGINE MECHANICAL
MEASURING CONNECTING ROD BEARING CLEARANCE
Connecting rod bearings are of the precision insert
type and do not use shims for adjustment. DO NOT
FILE RODS OR ROD CAPS. If clearances are found to
be excessive, a new bearing (both upper and lower
halves) will be required.
The simplest, most accurate way to measure con­
necting rod bearing clearance is with the use of gaging
plastic. This wax-like material compresses evenly
between the bearing and journal surfaces with damag­
ing them. Proceed as follows.
• All oil from the crankshaft journal and the connect­
ing rod bearing inserts.
[■»*■] install or Connect (Figure 39)
• Refer to the proper section for additional informa­
tion on connecting rod bearing sizing.
1. Connecting rod with the upper connecting rod
bearing insert to the crankshaft journal.
2. A piece of gaging plastic the length of the bearing
(parallel to the crankshaft) on the journal (figure
39). The plastic gage should be positioned in the
middle of the upper and lower bearing insert.
(Bearings are eccentric and false readings could
occur if placed elsewhere.)
| Important
• If a bearing is being fitted to an out-of-round
crankpin, be sure to fit the maximum diameter
of the crankpin. If the bearing is fitted to the
minimum diameter and the crankpin is exces­
sively out-of-round, interference between the
bearing and the crankpin will result in rapid
bearing failure.
3. Connecting rod cap with the lower connecting rod
bearing insert. DO NOT TURN THE CRANK­
S H A F T WI TH THE GAGI NG
INSTALLED.
4. Connecting rod cap nuts.
|$ G Tighten
• Nuts to " Specifications." Refer to the proper
section.
| Important
• The gaging plastic will be found sticking either to
the journal or lower connecting rod bearing insert.
Do not remove it at this time.
Clean (Figure 40)
• Gaging plastic at its widest point, using the scale
at the gaging plastic envelope (figure 40).
• If the clearance exceeds specifications, select a
new, correct size, connecting rod bearing and
remeasure the clearance.
• A standard or undersize bearing may produce the
proper clearance. Refer to the proper section for
bearing availability.
• Do not attempt to use shims or file the bearing to
obtain the needed clearance.
• If clearance cannot be brought to within specifica­
tions, recondition or replace the crankshaft. (Do
not recondition a rolled fillet crankshaft, such as
used on 2.5L, 2.8L, and 6.2L engines.)
(<--►1 Remove or Disconnect
• Gaging plastic.
P L A S T I C
A. Measure Widest Point of Gaging
Plastic with Graduated Scale
Figure 40—Measuring the Gaging Plastic
Connecting Rod Journal
I
B4997