TM 55-1930-209-14&P-21
Section IX. Pistons, Connecting Rod and Cylinder Liners
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General
a.
Pistons and piston rings
(1)
The trunk type malleable iron piston (Figure 6-27) is plated with a protective coating of tin which permits
close fitting, reduces scuffing and prolongs piston life. Top of piston forms combustion chamber bowl and is designed to
compress air into close proximity to fuel spray.
(2)
Piston is cooled by a spray of lubricating oil directed at underside of piston head from a nozzle in top of
connecting rod, by fresh air from blower to top of piston, and indirectly by water jacket around cylinder.
(3)
Two bushings with helical grooved oil passages are pressed into piston to provide a bearing for hardened,
floating piston pin. Each end of piston pin is sealed with a piston pin retainer.
(4)
Each piston is fitted with six piston rings. Four compression rings are installed above piston pin and two,
three piece oil control rings are installed below piston pin, eight equally spaced holes are drilled just below each oil
control ring to permit excess oil to return to crankcase.
b.
Connecting rods
(1)
Each connecting rod is made of forged steel. The rod is drilled to provide lubrication to piston at upper end
and is equipped with an oil spray nozzle for cooling piston.
(2)
Connecting rod bearing shells are different and not interchangeable.
(3)
A helically-grooved bushing is pressed into each side of connecting rod at upper end. A cavity of
approximately 1/8 inch between inner ends of bushings, registering with the drilled oil passage in rod, forms a duct
around piston pin for lubrication.
(4)
Connecting rod bearings are prevented from movement by a tang at parting line of each shell. Each
connecting rod cap is numbered.
c.
Cylinder liners
(1)
Cylinder liners are of replaceable wet type, made of hardened alloy cast iron, and are a slip fit in cylinder
block. They are installed in cylinder bores from top. A flange on each liner rests on a counterbore in top of block.
(2)
A synthetic rubber cylinder liner seal ring recessed in cylinder block bore between liner and block prevents
water leakage.
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