Inspection and Repair - TM-10-3930-634-340112

TM 10-3930-634-34

(a) Remove rear main bearing cap (fig. 3-131)

(2) If the crankshaft has been subjected to ex-

and remove lower thrust washer halves and lower

cessive overheating, the heat treatment will be de-

bearing shell.

stroyed and a new crankshaft should be installed.

(b) Remove upper thrust washer halves by push-

(3) Used crankshafts will sometimes show a cer-

ing on one side with a small rod, forcing washer

tain amount of ridging caused by the groove in the up-

around and out on opposite side of the journal (fig.

per main bearing shell or lower connecting rod bearing

3-132).

shell (fig. 3-135, A). Ridges exceeding 0.0002 inch

(c) Remove the upper rear main bearing shell by

must be removed. If the ridges are not removed, local-

driving on the edge of the shell with a small curved

ized high unit pressures on new bearing shells will re-

rod, at the same time rotating the crankshaft. This

sult during engine operation.

(4) The ridges may be removed by working crocus

will roll the bearing shell from its position.

cloth, wet with fuel oil, around the circumference of

c. Removal of Crankshaft and Main Bearings.

the crankshaft journal. If the ridges are greater than

(1) Remove engine (para 2-5).

0.0005 inch, first use 120 grit emery cloth to cleanup

(2) Remove rocker arm covers (para 3-16) and re-

the ridge, 240 grit emery cloth for finishing, and wet

move fuel oil pipes. Install dust caps on injector and

crocus cloth for polishing. Use of a piece of rawhide or

fuel connectors.

other suitable rope wrapped around the emery cloth or

(3) Pivot the rocker arms away from the valve

crocus cloth and drawn back and forth will minimize

stems (para 3-23). This step is necessary to prevent

the possibility of an out-of-round condition developing

damage to valves and valve stems should a piston

assembly be allowed to drop or pushed down on the

(keep the strands of rawhide apart to avoid bind). If

valves.

rawhide or rope is not used, the crankshaft should be

rotated at intervals. If the ridges are greater than

(4) Remove oil pan (para 3-26) and oil inlet tube

0.001 inch the crankshaft may have to be reground.

(para 3-27).

(5) Carefully inspect the front and rear end of the

(5) Remove lower front cover and oil pump (para

crankshaft in the area of the oil seal contact surface

3-31).

for evidence of a rough or grooved condition. Any

(6) Remove flywheel housing (para 3-33).

imperfections of the oil seal contact surface will result

(7) Remove the connecting rod bearing caps (para

in oil leakage at this point.

3-34). Push the piston assemblies toward the cylinder

(6) Slight ridges on the crankshaft oil seal contact

head until the connecting rod bolts are clear of the

surfaces may be cleaned up with emery cloth and cro-

crankshaft.

NOTE

cus cloth in the same manner as detailed for the crank-

shaft journals. If the crankshaft cannot be cleaned up

It maybe necessary to push one of the valves

satisfactorily, replace the crankshaft..

open to expel air from the cylinder chamber

(7) Check the crankshaft thrust surfaces for ex-

when pushing piston into block.

cessive wear or grooving. If only slightly worn, the

(8) Remove main bearing caps and lower bearing

surfaces may be dressed up with a stone. Otherwise, it

shells (figs, 3-129 and 3-131).

will be necessary to regrind the thrust surfaces.

(9) Attach a suitable sling to crankshaft (19, fig.

(8) Check the crankshaft timing gear for worn or

3-130), and remove the crankshaft from the cylinder

chipped teeth. Replace the gear if necessary.

block. Remove upper bearing shells (9 and 12) from

(9) Support the crankshaft on its front and rear

main bearing supports.

d. Disassembly.

journals on V-blocks or in a lathe and check the aline-

ment at the adjacent intermediate main journals with

(1) Remove the crankshaft timing gear with a

a dial indicator.

suitable gear puller (fig. 3-133).

(10) The maximum runout on the intermediate

(2) If the oil pump drive gear requires replace-

journals must not exceed 0.002 inch total indicator

ment, install the crankshaft pulley retaining bolt into

reading.

end of crankshaft and remove the gear with puller as

(11) When the runout on the adjacent journals is

shown in figure 3-134.

e. Cleaning.

in opposite directions, the sum must not exceed 0.003

(1) Remove crankshaft plugs and clean out the oil

inch total indicator reading. When the runout on the

adjacent journals is in the same direction, the differ-

passages thoroughly with a stiff wire brush,

ence must not exceed 0.003 inch total indicator read-

( 2 ) Clean the crankshaft, bearing shells and

ing. When high spots of runout on the adjacent jour-

timing gear with cleaning solvent P-D-680. Dry

nals are at right angles to each other, the sum must

thoroughly with compressed air and reinstall plugs.

f. Inspection and Repair.

not exceed 0.004 inch total indicator reading, or 0.002

inch on each journal. If the runout limit is greater than

(1) Inspect the keyways for evidence of cracks or

given above, the crankshaft must be replaced.

wear, Replace the crankshaft, if necessary.

3-34