TM 5-3810-300-24-&P-3
Piston and Piston Rings 1.6
CROSS-HEAD TYPE PISTON
The cross-head piston (Figs. 14 and 15) is a two-piece
as the piston crown expands. As the connecting rod
piston consisting of a crown and skirt. A metal oil seal
swings to one side during downward travel of the piston,
ring is used between the crown and skirt which are held
the major portion of the side load is taken by the piston
together by the piston pin. Ring grooves are machined in
skirt.
the piston crown for a fire ring and two compression
The non-turbocharged (naturally aspirated) engines use
rings. The crown is also machined to accept a 150'
an 18.7:1 compression ratio piston.
slipper type bushing (bearing).
The piston skirt
incorporates two oil control ring grooves, piston pin holes
and piston pin retainer counterbores. Equally spaced
CAUTION: Cross-head pistons and trunk-
drain holes are located in the oil ring groove area to
type pistons must not be used together in an
permit excess oil, scraped from the cylinder walls, to
engine. The difference in weight of the
return to the crankcase. A lubricating oil tube and
pistons will affect engine balance.
floating nut are contained inside of the piston pin. Two
bolts and spacers are used to attach the connecting rod
Inspect Piston Rings
(Section 1.6.1) to the floating nut in the piston pin.
When an engine is hard to start, runs rough or lacks
Internal parts of the piston are lubricated and cooled by
power, worn or sticking compression rings may be the
the engine lubricating oil. Oil is pressure-fed up the
cause. Replacing the rings will aid in restoring engine
drilled passage in the connecting rod, through the oil
operation to normal.
tube in the piston pin, then through the center hole in the
bushing to the underside of the piston crown. A portion
The compression rings may be inspected through the
of the oil flows along the grooves in the bushing to
ports in the cylinder liners after the air box covers have
lubricate the piston pin.
been removed. If the rings are free and are not worn to
the extent that the plating or grooves are gone,
During engine operation, gas loads pushing down on the
compression should be within operating specifications.
piston crown are taken directly by the piston pin and
bushing. The piston skirt, being separate, is free from
compression pressure.
vertical load distortion; thermal distortion is also reduced
Fig. 15 - Cross-Head Piston and Connecting Rod
Components
Fig. 14 - cross-Head Piston and Connecting Rod
Assembly
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