Chevrolet 10 series 1973, Руководство по капитальному ремонту

Страница: 160 / 522

E N G IN E 6 -1 9
M A IN BEARINGS
Main bearings are of the precision insert type and do
not utilize shim for adjustment. If clearances are found
to be excessive a new bearing, both upper and lower
halves will be required. Bearings are available in
standard size and .001", .002", .009", .010",.020" and
.030" undersize.
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.
When a production crankshaft cannot be precision fitted
by this method, it is then ground .009" undersize
on
main journals only. A .0 0 9 " undersize bearing and .010"
undersize bearing may be used for precision fitting in
the same manner as previously described. Any engine
fitted with a .009" undersize crankshaft will be
identified by the following markings.
• ".009" will be stamped on the crankshaft
counterweight forward of the center main
journal.
• A figure "9" will be stamped on the block at the
left front oil pan rail.
NOTE: If, for any reason, main bearing caps
are replaced, shimming may be necessary.
Laminated shims for each cap are available
for service. Shim requirement will be
determined by bearing clearance.
Inspection
In general, the lower half of the bearing (except No. 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.
Checking Clearance
To obtain the most accurate results with "Plastigage", (or
its equivalent) a wax-like plastic material which will
compress evenly between the bearing and journal
surfaces without damaging 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 journal. If the
engine is to remain in the vehicle, the crankshaft should
be supported both front and rear (damper and flywheel)
to remove the clearance from the upper bearing. The
total clearance can then be measured between the lower
bearing and journal.
NOTE: To assure the proper seating of the
crankshaft all bearing cap bolts should be at
their specified torque. In addition, prepara­
tory to checking fit of bearings, the surface of
the crankshaft journal and bearing should be
wiped clean of oil.
1. With 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.
2. Place a piece of gauging plastic the full width of
the bearing (parallel to the crankshaft) on the
journal (fig. 39).
CAUTION:
Do not rotate the crankshaft while
the gauging plastic is between the bearing and
journal.
3. Install the bearing cap and evenly torque the
retaining bolts to specifications.
4. Remove bearing cap. The flattened gauging plastic
will be found adhering to either the bearing shell or
journal.
5. On the edge of gauging plastic envelope there is a
graduated scale which is correlated in thousandths
of an inch. Without removing the gauging plastic,
measure its compressed width (at the widest point)
with the graduations on the gauging plastic
envelope (fig. 40).
NOTE: 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 (.001" max.), be sure to
fit to the maximum diameter of the journal:
If the bearing is fitted to the minimum
diameter and the journal is out-of-round
Fig. 39—Gauging Plastic on Journal
OVERHAUL MANUAL