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 TM 55-1905-217-34
greater than the thickness of the feeler gage used, i.e., a .004 inch feeler gage will indicate a .050 inch clearance when
it is withdrawn with a six pound pull. The feeler gage must be perfectly flat, and free of nicks and bends.
(f) If any bind occurs between the piston and liner, remove the piston and examine the piston and liner for burrs.
Remove burrs with a fine hone (a flat one is preferable) before proceeding with the clearance check.
(7) Fitting Piston Rings. All new piston rings must be installed whenever a piston is removed, regardless of
whether a new or used piston or cylinder liner is installed.
(a) Insert one ring at a time inside of the cylinder liner and far enough down in the bore to be within the normal
area of the ring travel. Use a piston to push the ring down to be sure it is parallel with the top of the liner. Then,
measure the ring gap with a feeler gage. The ring gaps are specified in table 1-2.
(b) If the piston ring gap is insufficient, it may be increased by filing or stoning the ends of the ring. File or stone
both ends of the ring so the cutting action is from the outer surface to the inner surface. This will prevent any chipping
or peeling of the chrome plate on the compression ring. The ends of the ring must remain square and the chamfer
must be approximately .015 inch on the outer edge.
(c) Check the ring clearance in the piston ring grooves. The piston ring clearances are shown in table 1-2.
NOTE
Before installing rings, the connecting rod and piston should be assembled.
(a) Install the compression rings on the piston with tool J 8128. To avoid breaking or overstressing the rings, do
not spread them any more than necessary to slip them over the piston.
(b) Install the oil control rings by hand. The scraping edges must face toward the bottom of the piston for
proper oil control. First, install the expander carefully in the upper oil ring groove. Next, install the top ring with the gap
180from the gap in the expander. Then, install the bottom ring with the gap 45from the gap of the upper ring. Install
the second oil control ring in the lower oil ring groove in the same manner.
(c) When installing the oil control rings, care must be exercised to prevent overlapping the ends of the oil control
ring expanders. The expanders must be correctly seated inside the piston oil control ring grooves. An overlapped
expander will cause the oil control ring to protrude beyond allowable limits. A protruding oil control ring will be broken
when the piston is installed in a ring compressor or when the piston and rod assembly is installed in the cylinder liner.
(d) If there is a noticeable resistance during installation of the piston, check for overlapped oil control ring
expander ends.
NOTE
Do not cut or grind off the ends of the oil ring expanders to keep them from overlapping.
Cutting or grinding the ends will decrease the expanding force on the oil control ring and
result in high lubricating oil consumption.
(9) Assemble Connecting Rod to Piston. Apply clean engine oil to the piston pin and bushings. Assemble the
connecting rod to the piston as follows:
(a) Rest the piston in the holding fixture J 1513-1.
(b) Place a new piston pin retainer in position. Then, place the crowned end of installer J 4895-01 against the
retainer and strike the tool just hard enough to deflect the retainer and seat it evenly in the piston.
NOTE
Do not drive the retainer in too far or the piston pin bushing may be moved inward and
result in reduced piston pin end clearance.
(c) Place the upper end of the connecting rod between the piston pin bosses and in line with the piston pin
holes. Then, slide the piston pin in place. If the piston pin-to-bushing clearances are within the specified limits, the pin
will slip into place without use of force.
(d) Install the second piston pin retainer as outlined in steps (a) and (b).
(e) After the piston pin retainers have been installed, check for piston pin end clearance by "cocking" the
connecting rod on the pin and shifting it in its bushings.
(f) One important function of the piston pin retainer is to prevent the oil, which cools the underside of the piston
and lubricates the piston pin bushings, from reaching the cylinder walls. Check the retainers for proper sealing as
follows:
1. Place the piston and connecting rod assembly upside down on a bench.
2. Pour clean fuel oil in the piston to a level above the piston pin bosses.
3. Dry the external surfaces of the piston in the area around the retainers, and allow the fuel oil to set for
about fifteen minutes.
4. Check for seepage of fuel oil around the retainers. If the fuel oil leads around the retainers, install
new retainers. In extreme cases, it may be necessary to replace the piston.
5. After the leakage test is completed, empty the fuel oil from the piston, dry the parts
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