GMC 1982 Light Duty Truck, Руководство по обслуживанию

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6A5-22 M A R K IV
a. Place a piece of gaging plastic, the length of the
bearing (parallel to the crankshaft), on the crankpin
or bearing surface (fig. 6A5-41). Plastic gage should
be positioned in the middle of upper or lower bearing
shell. (B earings are eccentric and false readings
could occur if placed elsewhere).
b. Install the bearing in the connecting rod and cap.
c. Install the bearing cap and evenly torque nuts to
specifications. Do not tu rn the crankshaft with the
gaging plastic installed.
d. Remove the bearing cap and using the scale on the
gaging plastic envelope, measure the gaging plastic
width at the widest point (fig.6A5-42).
6. If the clearance exceeds specifications, select a new,
correct size, bearing and remeasure the clearance. Be
sure to check what size bearing is being removed in
order to determine proper replacement size bearing.
If clearance cannot be brought to within specifications,
the crankpin will have to be ground undersize. If the
crankpin is already at maxim um undersize, replace
crankshaft.
7. Coat the bearing surface with oil, install the rod cap
and torque nuts to specifications.
8. W hen all connecting rod bearings have been installed
tap each rod lightly (parallel to the crankpin) to make
sure they have clearance.
9. Measure all connecting rod side clearances (see speci­
fications) between connecting rod caps (fig. 6A5-43).
M A IN BEARINGS
Main bearings are of the precision insert type and do
not utilize shims for adjustm ent. If clearances are found to
be excessive, a new bearing, both upper and lower halves,
will be required. Service bearings are available in standard
size and .001", .002 ", .009 " , . 0 1 0 " and .020 " undersize.
Fig. 6A5-43--Measuring Connecting Rod Side
Clearance
Selective fitting of both rod and main bearing inserts is
necessary in production in order to obtain close tolerances.
For this reason you may find one half of a standard insert
with one half of a .001" undersize insert which will decrease
the clearance .0005 " from using a full standard bearing.
Inspection
In general, the lower half of the bearing (except # 1
bearing) shows a greater wear and the most distress from
fatigue. If upon inspection the lower half is suitable for use,
it can be assumed that the upper half is also satisfactory. If
the lower half shows evidence of wear or damage, both upper
and lower halves should be replaced. Never replace one half
without replacing the other half.
C hecking C learance
To obtain the most accurate results with " P las tig ag e" ,
(or its equivalent) a wax-like plastic m aterial which will
compress evenly between the bearing and journal surfaces
without dam aging either surface, certain precautions should
be observed.
If the engine is out of the vehicle and upside down, the
crankshaft will rest on the upper bearings and the total
clearance can be measured between the lower bearing and
jo u rn a l. If the engine is to re m a in in the vehicle, the
c ra n k s h a ft m ust be supported up w ard to remove the
clearance from the upper bearing. The total clearance can
then be measured between the lower bearing and journal.
To assure the proper seating of the crankshaft, all
bearing cap bolts should be at their specified torque. In
addition, preparatory to checking fit of bearings, the surface
of the crankshaft journal and bearing should be wiped clean
of oil.
1. W ith the oil pan and oil pump removed, and starting
with the rear main bearing, remove bearing cap and
wipe oil from journal and bearing cap.
Fig. 6A 5 -42--M easuring G ag ing Plastic