Section VIII. BEARINGS

TM 10-3930-621-34

d. Use a wooden hammer handle to force piston

through the ring compressor into the cylinder bore. Keep

f. Install lower half of connecting rod bearing in

the ring compressor tight against the cylinder block to

connecting rod bearing cap and install cap, nuts, and

prevent ring damage.

cotter pins.

e. Oil crankshaft journal with internal combustion

g. Tighten connecting rod bearing cap nuts to 44-46

engine lubricating oil (OE). Install upper half of bearing

foot-pounds of torque. h. Install oil pan (para 3-40),

into connecting rod, and seat bearing on crankshaft

cylinder head (TM 10-3930-621-12), and engine (para 2-

journal.

5).

Section VIII. BEARINGS

bearing cap nuts. Pull down on all nuts evenly, going

3-31. Replacement

from one side of the bearing to the other. Apply final

a. General. Both the connecting rod and main

tension with a torque wrench, using a slow steady pull

bearings are of the steel-backed, precision type. Due to

and holding the wrench "on torque" for a few seconds

the close machining of this type of bearing, not fitting,

when the proper value is reached. It is preferable to go

filing, scraping, boring or other adjustment is required or

to a slightly higher tension if necessary. Previous over-

permissible. Replacement must be in complete bearings

torquing or some other damage to the bolt or nut is

units. Never replace (only one half of a bearing. Service

sometimes encountered and will be felt by the torque

bearings are available in standard size only. Never

"softening up" so that the nut can be turned without any

attempt to adjust a bearing by filing, grinding, or lapping

appreciable increase in wrench tension. Never allow a

the hearing cap. The bearing seats are precision ground

bolt or a nut in this condition to remain on the engine.

with the caps in place. Any metal removed from neither

side prevents the proper fit of a connecting rod bearing in

3-34. Main Bearing Crush

the rod and, makes the entire engine block unsuited for

The term "crush" is generally understood to mean the

use.

projection of the bearing edges above flush with the

b. Emergency Replacement of Main Bearings. In' an

mating surfaces of the bearing seat and cap. This

emergency a main bearing may be replaced without

crushing action forces the bearing halves into close

removing the crankshaft. This type of repair is to be

contact with their seats for greater rigidity and good heat

confined to emergency field conditions only.

conduction. The correct amount of crush has been

Disassemble engine as necessary.

allowed during the manufacture of the bearings and no

(1) Remove the bearing cap and its bearing

attention to that detail is necessary at the time of

shell.

replacement. The use of a torque wrench for tightening

(2) Place a soft brass or aluminum strip against

bearings is necessary to insure sufficient "crush" on the

an exposed edge of the upper bearing and firmly push

bearings to force the shells against the engine block

the hearing around the crankshaft journal.

metal without distortion.

(3) Inspect and replace both bearings as

3-35. Running Clearance Tests

necessary. Never replace one alone.

a. Connecting Rod. The test of connecting rod

(4) Inspect journal surface for roughness, out-

bearing clearance consists of manually gripping the rod

of-round, or undersize; any of which greatly reduce

cap, after the bearing bolts are tightened, and attempting

bearing life. For best performance and reliability it is

to move the rod from side to side in the direction of end

recommended that the crankshaft be removed so that

clearance. A well fitted bearing is usually loose enough

adequate inspection and checks, for conformance to

to be "snapped" from side to side without actually feeling

design tolerance may be preformed.

so loose as to push easily. Sometimes a slightly snug

3-32. Cleaning

bearing will not move under pressure, but will move

Be sure the bearings seat on absolutely clean surfaces

readily under light blows from a soft-faced hammer. This

and that the back of the bearings are wiped clean. The

test usually is considered satisfactory, providing the

slightest bit of dirt or carbon squeezed between the back

engine has been given adequate break-in time.

of a bearing and its seat can cause rapid bearing failure

b. Main Bearing. Generally the test on main bearings

by developing a localized high spot.

consists of tightening each bearing cap in turn and

turning the crankshaft to detect binding. one accurate

3-33. Torquing

test is:

Equally important in obtaining maximum bearing life is

the correct tension on the connecting rod

3-14