GMC 1982 Light Duty Truck, Руководство по обслуживанию

Страница: 746 / 1435

6A7-18 6.2 DIESEL
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 h ec kin g C le a ra n c e
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 must be supported upward 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. 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 gaging plastic the full width of the
bearing (parallel to the crankshaft) on the journal (fig.
6A7-33). Do not rotate the crankshaft while the gaging
plastic is between the bearing and journal.
3. Install the bearing cap and evenly torque the retaining
bolts to specifications. Bearing cap M UST be torqued
to specifications in order to assure proper reading.
Variations in torque affect the compression of the
plastic gage.
4. Remove bearing cap. The flattened gaging plastic will
be found adhering to either the bearing shell or journal.
5. On the edge of gaging plastic envelope there is a
graduated scale which is correlated in thousandths of
an inch. Without removing the gaging plastic, measure
its compressed width (at the widest point) with the
graduations on the gaging plastic envelope (fig. 6A7-
34). Normally main bearing journals wear evenly and
are not out-of-round. However, if a bearing is being
fitted to an out-of-round (.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 .001 ", interference between the bearing and
journal will result in rapid bearing failure. 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.
Be sure to measure the journal with a micrometer if the
flattened gaging plastic indicates more than .001"
difference.
6. If the bearing clearance is within specifications # 1 , 2 ,
3, 4 (.0018" -.0032" ) and # 5 (.0022" - .0037"), the
bearing insert is satisfactory. If the clearance is not
within specifications, replace the insert. Always replace
both upper and lower inserts as a unit. If a new bearing
cap is being installed and clearances are less than
.001", inspect for burrs or nicks; if none required, then
install shims as required.
7. A standard, .001" or .002" undersize bearing may
produce the proper clearance. If not, it will be
necessary to regrind the crankshaft journal for use with
the next undersize bearing. After selecting new
bearing, recheck clearance.
8. Proceed to the next bearing. After all bearings have
been checked rotate the crankshaft to see that there is
no excessive drag. When checking # 1 main bearing,
loosen accessory drive belts so as to prevent tapered
reading with plastic gage.
9. Measure crankshaft end play (see specifications) by
forcing the crankshaft to the extreme front position.
Measure at the front end of the rear main bearing with
a feeler gage (fig. 6A 7-35).
10. Install a new rear main bearing oil seal in the cylinder
block and main bearing cap.
R e p la c e m e n t
Main bearings may be replaced with or without
removing the crankshaft.
With Crankshaft Rem oval
1. Remove and inspect the crankshaft.
2. Remove the main bearings from the cylinder block and
main bearing caps.
3. Coat bearing surfaces of new, correct size,
mainbearings with oil and install in the cylinder block
and main bearing caps.
4. Install the crankshaft.
Without Crankshaft Rem oval
1. With oil pan, oil pump and glow plugs removed, remove
cap on main bearing requiring replacement and remove
bearing from cap.
2. Install a main bearing removing and installing tool in
oil hole in crankshaft journal. If such a tool is not
available, a cotter pin may be bent as required to do the
job.
3. Rotate the crankshaft clockwise as viewed from the
front of engine. This will roll upper bearing out of
block.
4. Oil new selected size upper bearing and insert plain
(unnotched) end between crankshaft and indented or
notched side of block. Rotate the bearing into place and
remove tool from oil hole in crankshaft journal.
5. Oil new lower bearing and install in bearing cap.
6. Install main bearing cap.
7. Torque all main bearing caps EXCEPT THE REAR
M A IN C A P to specifications. Torque rear main
bearing cap to 10-12 lb. ft. (14-16 N-m) then tap end of
crankshaft, first rearward then forward with a lead
hammer. This will line up rear main bearing and
crankshaft thrust surfaces. Retorque all main bearing
caps to specifications.
OIL SEAL-REAR M A IN
R ep air
1. Remove oil pan and oil pump as previously outlined.
2. Remove rear main bearing cap.