Crankshaft - TM-10-3930-242-340112

TM 10-3930-242-34

NOTE

not exceed 0.003 inch total indicator reading.

If the bearings have been installed properly, the

When runout on adjacent journals is in the

crankshaft will turn freely with all main bearing

s a m e direction, the difference must not exceed

caps bolted tight.

0 . 0 0 3 inch total indicator reading. When high

(4) Check crankshaft end play at thrust

spots or runout on adjacent journals are at

washers. This clearance should be from 0.004 to

r i g h t angles to each other, the sum must not

0 . 0 1 1 inch. Insufficient clearance will usually

e x c e e d 0.004 inch total indicator reading, or

d e n o t e misalignment of the rear main bearing.

0 . 0 0 2 inch on each journal. If runout limit is

In such case, loosen and retighten the rear main

greater than given above, crankshaft must be

bearing cap. If lack of clearance is still present,

replaced.

dirt or a bur on inner face of one or more of the

( 3 ) Measure all main and connecting rod

thrust washers may be the cause, or washer

b e a r i n g journals. Journals should be measured

m a y be bent.

a t several places on the circumference in order

NOTE

t o determine the smallest diameter, in case the

j o u r n a l s have worn out-of-round. Taper on the

If end play has increased to the point where clear-

journals of a used shaft should not exceed 0.003

ance is in excess of 0.004-0.011 inch, new washers

should be installed.

i n c h , and out-of-round should not exceed 0.003

(5) Install

lubricating oil pump inlet pipe

i n c h . The maximum taper on a new shaft is

a s s e m b l y (para

3-25).

0.0005 inch and maximum out-of-round is 0.0025

(6) Install

o i l pa n w i t h ne w ga s k e t (p a r a

inch.

3-24).

(4) Used crankshafts will sometimes show a

( 7 ) Install

the engine (para 2-5).

certain amount of ridging caused by the groove

in the upper main bearing shell. If this ridge is

3-32. Crankshaft

n o t removed before new bearing shells are in-

a. General. The crankshaft is secured to the

s t a l l e d , localized high unit pressures on the

e n g i n e block by means of main bearings. The

b e a r i n g s will result during engine operation. A

c r a n k s h a f t has four journals on which connect-

r i d g e exceeding 0.0002 inch or more must be

i n g rods are mounted with enough clearance so

r e m o v e d . If ridges are greater than 0.001 inch,

that they will move freely over surface of crank-

t h e crankshaft may have to be replaced.

shaft.

( 5 ) Check surfaces of the crankshaft for

b. Removal.

e v i d e n c e of cracks as follows: Several methods

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

of determining presence of minute cracks not

(2) Remove oil pan (para 3-24).

r e a d i l y visible to the eye are-

( 3 ) Remove oil screen and inlet pipe (para

(a) M a g n e t i c Particle Method

3-25).

(b) F l u o r e s c e n t

Magnetic

Particle

(4) Remove flywheel housing (para 3-22).

Method

( 5 ) Remove front cover and oil pump (para

(c) F l u o r e s c e n t Penetrant Method

3-2).

(6) Remove rocker arm cover (TM

NOTE

10-3930-242-12), then remove fuel oil pipes from

Most of the indications revealed by the above in-

i n j e c t o r s and fuel connectors. Install dust caps

s p e c t i o n methods are normal and harmless and

on injectors and fuel injectors. (para 3-13).

only in a small percentage of cases is reliability of

(7) Loosen all rocker arm shaft support

t h e part impaired when indications are found.

Since inspection reveals harmless indications

b r a c k e t bolts to prevent valves from opening

with the same intensity as the harmful ones, de-

w h e n crankshaft is rotated (para 3-15).

tection is but one step in the procedure. Interpre-

( 8 ) Refer to figure 3-62 and remove crank-

t a t i o n of the indications is the most important

shaft.

step.

c . Cleaning, Inspection, and Repair.

(1) Remove crankshaft plugs and clean out

( 6 ) Check thrust surfaces for evidence of

all oil passages thoroughly, using solvent

e x c e s s i v e wear or roughness. In many instances

P-D-680, or equal.

only slight grinding or "dressing up" of the

t h r u s t surfaces is necessary. In such cases, use

(2) Support crankshaft on its front and rear

o f new standard thrust washers will probably

j o u r n a l s in a V-block or in a lathe and check

hold the end thrust clearance within the

runout on intermediate main bearing journals,

specified limits of 0.004-0.011 inch for new parts

using a dial indicator. When runout on adjacent

or a maximum of 0.018 inch with a used crank-

j o u r n a l s is in opposite direction, the sum must

3-72