Cleaning, Inspection, and Repair. - TM-55-4920-226-150111

(4) and remove the piston from the

(7) Check the piston pin sleeve bearing

for wear, scoring, and out-of-round.

connecting rod.

The clearance between the piston pin

(2) Remove the piston rings (1, 2, and 3)

and bearing should not exceed 0.001

from the piston.

inch. Replace a defective bearing.

(3) Press the sleeve bearing (11) out of

(8) Inspect the bearing halves for wear or

the connecting rod if defective or un-

scoring. Replace both bearing halves

serviceable.

if either is unserviceable. Measure the

(4) Disassemble the other pistons and con-

bearing-to-crankshaft clearance by in-

necting rods in the same manner.

stalling a piece of 0.001 inch shim

c. Cleaning, Inspection, and Repair.

stock on each bearing half. Assemble

(1) Clean carbon from the top of the pis-

t h e connecting rod and cap with

tons. Wash all parts with an approved

s h i m m e d bearing to its respective

cleaning solvent and dry thoroughly.

crankshaft journal and tighten the

nuts to a torque of 14 to 18 ft-lb. A

(2) Use an inside micrometer to measure

slight drag on the shaft, when turned

the cylinder bores for wear. All cylin-

by hand indicates proper clearance.

ders should measure 3.504 to 3.505

The connecting rod bearing should not

inches. Remove, rebore, and hone the

bind using shim stock with a minimum

the cylinder blocks (par. 199) whose

thickness of 0.0005 inch.

measurement exceeds the allowable

wear of 0.005 inch and install oversize

d. Reassembly.

pistons and rings.

(1) Press the sleeve bearing (11, fig. 36)

into the connecting rod (12). Ream

(3) To measure the piston ring gap, place

and hone new bearings (11) to provide

the ring in the cylinder bore in the ap-

a clearance of from 0.0005 to 0.001

proximate operating position and

inch between the piston (6) and the

measure the gap with a feeler gage.

bearing.

The piston ring gaps should meas-

Note. Be sure to aline the oil holes of the

ure between 0.010 and 0.015 inch. If

connecting rod and bearing.

the gap is too great replace the piston

(2) Position the piston on the connecting

ring with an oversize ring. If the gap

rod and install the piston pin (6) and

is too small remove stock by filing.

the two retaining rings (5).

(4) Place two strips of 0.002 inch shim

(3) Install the oil piston ring (3) in the

stock 1/2 inch wide, on opposite sides

bottom groove of the piston (4) with

of the piston. Invert the piston and

its scraper edge down. Install the

slide it into the cylinder bore. Attach

scraper piston ring (2) in the adja-

a spring pull scale to one of the pieces

c e n t groove with its scraper edge

of shim stock and pull up on the scale.

down. Install the two remaining pis-

A pull of 4 to 8 pounds should be re-

ton rings (1) in the upper grooves.

quired to pull the stock out. If the

Stagger the ring gaps around the pis-

shim stock pulls out too freely replace

ton.

the piston with an oversized one. Re-

(4) Reassemble the three remaining pis-

bore and rehone the cylinder bore as

tons and connecting rods in a similar

necessary.

manner.

(5) Measure the piston ring side clear-

ance. Replace the piston when clear-

e. Installation.

ance exceeds 0.003 inch in the three

(1) Place a ring compressor on the piston.

top grooves or 0.004 inch in the bot-

(2) Insert the connecting rod (12, fig. 36)

tom groove.

with attached piston in its respective

(6) Measure the piston pin fit in the pis-

cylinder bore and push piston out of

ton. If the clearance exceeds 0.0005

the ring compressor into the cylinder

inch, replace the piston and piston pin.

block.

107

AGO 5742A