chevrolet truck Light Duty Truck 1994 Series, Repair Manual

Page: 315 / 919

4. Normally main bearing journals wear evenly and
are not out-of-round. However, if a bearing is being
fitted to an out-of-round journal, make sure to fit to
the maximum diameter of the journal. If the bearing
is fitted to the minimum diameter and the journal is
excessively out-of-round, interference between the
bearing and the journal will result in rapid bearing
failure.
5. If the bearing clearance is within specifications, the
bearing is satisfactory. If the clearance is not within
specifications, replace the bearing. Always replace
upper and lower inserts as a unit.
A standard or undersize bearing may produce the
proper clearance. Refer to the proper section for
bearing availability. If not, it will be necessary to
regrind the crankshaft journal for use with the next
undersize bearing. Do not grind rolled fillet crank­
shafts. After selecting the new bearing, recheck the
clearance.
Remove the flattened gaging plastic.
Perform the preceding steps on the remaining main
bearings.
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 w ax-like m aterial com presses evenly
between the bearing and journal surfaces without dam­
aging them. Proceed as follows.
IQ I| Clean
• All oil from the crankshaft journal and the connect­
ing rod bearing inserts.
-►«- Install or Connect (Figure 28)
• Refer to the proper section for additional informa­
tion on connecting rod bearing sizing.
1. Connecting rod with the upper connecting rod bear­
ing insert to the crankshaft journal.
2. A piece of gaging plastic the length of the bearing
(parallel to the crankshaft) on the journal (figure
28). The gaging plastic should be positioned in the
middle of the upper and lower bearing insert (Bear­
ings 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 CRANKSHAFT
WITH THE GAGING PLASTIC INSTALLED.
4. Connecting rod bolt nuts.
NOTICE: Refer to “Notice” on page 6A-1.
Tighten
• Nuts to “ Specifications.” Refer to the proper
section.
Important
• The gaging plastic will be found sticking to either
the journal or lower connecting rod bearing insert.
Do not remove it at this time.