Inspection and Repair - TM-10-3930-634-340099

TM 10-3930-634-34

NOTE

(5) Fit the pistons on the cylinder liners as fol-

Move the piston to the bottom of its travel

lows:

and place a cloth on the top of the piston to

NOTE

collect cuttings. After reaming is completed,

If any bind between piston and liner is detect-

turn the crankshaft until the piston is at the

ed, remove the piston and inspect piston and

top of its stroke and carefully remove the

liner for burrs. Remove burrs with a fine

cloth with cuttings.

hone.

(a) Refer to table 1-1 and measure the piston

(5) Remove the piston and connecting rod assem-

skirt diameter and cylinder liner bore. Take these

as shown in figure 3-108.

measurements with the piston and liner at normal

c. Disassembly.

room temperature (72F).

(1) Disassemble the piston and connecting rod as-

(b) Refer to table 1-1 and check the piston to

sembly in numerical sequence as shown in figure

liner clearance. Check this in four places, 90 apart

3-109.

while holding the piston upside down in the cylinder

(2) Position the connecting rod and piston assem-

liner as shown in figure 3-111.

bly in a bench vise with soft jaws and remove the pis-

(c) The spring scale attached to the appropriate

ton rings with a ring expander as shown in figure

feeler gage is used to measure the force of pounds re-

3-110.

quired to withdraw the feeler gage from between the

(3) Punch a hole through the center of piston pin

piston and the liner. The clearance will be 0.001 inch

retainer (9, fig. 3-109) with a narrow chisel or punch

greater than the thickness of the feeler gage used

to pry the retainer from the piston (15).

when it is withdrawn at a pull of six pounds. The feeler

(4) Remove the piston (15) from the rod (12). Use a

gage must be flat and free of nicks and bends.

brass rod to remove the remaining retainer (9) from

(6) Fit the piston rings as follows:

the piston.

NOTE

(5) Do not remove piston or rod bushings (11 and

Use new piston rings whenever a piston is re-

14) or the rod spray nozzle (13), unless inspection indi-

moved for inspection or replacement.

cates replacement is required.

(a) Refer to table 1-1 and measure the gap be-

Cleaning.

tween the ends of the piston rings before installing

(1) Clean all parts with cleaning solvent P-D-680

rings on piston.

dry thoroughly with compressed air.

(2) Clean carbon from the top of the piston using a

wire brush.

(3) Using a suitable tool, clean the carbon from

the piston ring grooves.

(4) Use a suitable size drill and clean the carbon

from the eight oil control holes in the bottom of the

piston oil ring grooves.

e. Inspection and Repair.

(1) Inspect the pistons for scoring, overheating,

cracks or damaged ring grooves. A piston with light

score marks can be cleaned up and reused.

(2) Refer to table 1-1 and inspect and measure the

piston pins and pin bushings. -

(3) Replace the piston bushings as follows:

(a) Place the piston in a holding fixture and

drive the bushings from the piston.

(b) Place the fixture spacer in counterbore of

holding fixture, small end up. Place the piston on the

holding fixture so that the spacer protrudes into the

pin bushing bore.

(c) Locate the joint in the bushing toward the

of the piston, insert the installer handle and

drive the bushing in until it bottoms on the spacer.

(d) Install the opposite pin bushing in a similar

(4) Refer to table 1-1 and ream the piston pin

bushings to the value listed.

3-71