Wear limits. For allowable wear limits refer to table 1-1.

TM 10-3930-242-34

(f) The standard inside diameter of a new

must be perfectly flat and free from nicks and

bushing in a connecting rod is 1.3760-1.3765 in-

scratches.

ches. The specified clearance between the piston

NOTE

p i n and bushing in upper end of connecting rod

I f any bind between the piston and liner is de-

i s 0.0010-0.0019 inch with new parts, and the

t e c t e d , remove the piston and liner and inspect

a l l o w a b l e wear limit 0.010 inch. The piston pin

them for burs. If either part is marred, the parts

and/or rod bushings must be replaced if the

must be cleaned up, using a fine hone on the-liner

a b o v e limits are not obtained.

and fine file on the piston before proceeding.

(g) Visual inspection, as well as the di-

NOTE

m e n s i o n a l measurements will be made to de-

t e r m i n e whether used bearings are satisfactory

New piston rings should always be used whenever

a piston is removed for inspection or replacement.

f o r further service or must be replaced.

(j) When fitting piston rings, the gap bet-

(h) Inspect the back of the bearing shells

w e e n the ends of the rings should be measured

f o r bright spots which indicate they have been

b e f o r e installing the rings on the piston.

moving in their supports, If such spots are pres-

ent, discard the bearing shells. Also inspect

NOTE

connecting rod bearings bores for burs and

f o r e i g n particles.

The ring gap for the third compression ring and the

(i) Measure the thickness of the bearing

l o w e r compression ring is from 0.020-0.036 inch

s h e l l s and check the clearance between each

and the gap for the oil control ring is from

0.010-0.025 inch.

c o n n e c t i n g rod crank throw and the correspond-

ing bearing shells. Connecting rod cap nuts

(k) Check the ring clearances in the pis-

m u s t be tightened to 40-45 foot-pounds torque

ton grooves. Nominal ring groove widths, which

with the bearing shells in place when measuring

m a y vary 0.001 inch, and ring clearances in

t h e inside diameter. Use a micrometer and a

grooves should be as follows:

b a l l attachment, for measuring the shell thick-

ness. If the standard size bearing shells are less

Upper compression

than 0.123 inch in thickness and have more than

(fire) ring (straight

0 . 0 0 6 inch clearance between any crank throw

-0.010 in.

-0.007 in.

face)

and its bearings, all shells, both upper and

U p p e r compression

(fire) ring (tapered

l o w e r , must be discarded and new ones instal-

-0.006 in.

-0.003 in.

face)

led.

Second compression

-0.010 in.

-0.007 in.

NOTE

ring

-0.007 in.

-0.0045 in.

T h i r d compression ring

One connecting rod shell alone should not be re-

-0.007 in.

-0.0045 in.

L o w e r compression ring

placed. If one bearing shell requires replacement,

-0.0055 in.

-0.0015 in.

Upper oil control ring

both upper and lower shells should be installed.

-0.0055 in.

-0.0015 in.

Lower oil control ring

(4) Cylinder liner.

(2) Wear limits. For allowable wear limits

CAUTION

refer to table 1-1.

To avoid damage to the top land of piston,

(3) Connecting rod, piston pins, and bear-

do not at any time try to loosen cylinder

ings.

l i n e r by inserting a long bolt or rod

(a) Check rod for straightness. Hydrosta-

t h r o u g h the port openings in cylinder

t i c lock caused by fuel or water leakage to the

l i n e r and turning the crankshaft, thus

p i s t o n crown may result in a bent and possible

pushing the liner up with the piston.

b r o k e n connecting rod.

(a) When the cylinder liner is removed

(b) Check the connecting rods for cracks.

from the engine, it should be cleaned, and

(c) If nozzle type connecting rod, inspect

c h e c k e d for-out-of-round, taper, cracks, scor-

a n d open holes in spray nozzle at upper end of

i n g , flange irregularities, erosion.

connecting rod, if necessary. Blow dry compres-

(b) A cracked or excessively scored cylin-

sed air through drilled oil passage in rod nozzle

d e r liner must be discarded. A slightly scored

to be sure all passages are open.

c y l i n d e r liner may be cleaned up and reused.

(d) Check rod bushings for signs of scor-

(c) Install the cylinder liner in the block

i n g or other damage.

a n d measure the inside diameter of the liner at

(e) Measure the outside diameter of pis-

t h e various points shown in figure 3-52. If the

t o n pin to determine wear. The standard diame-

taper exceeds 0.002 inch or the out-of-round ex-

ter of new piston pins is 1.3746-1.3750 inches.

3-61