TM 5-3805-255-14
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ENGINE CONTINUED
Connecting Rods
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Connecting rods are forged steel and contain a bushing at upper end for installation on piston pins. This bushing is
lubricated by means of a collector cup in top of connecting rod. Oil from piston cooling jets drops into collector cup
and reaches bushing through a drilled passage. Lower end and cap contain locking-type, selective-fit bearing
inserts. Connecting rod and cap are held together using two connecting rod bolts and two nuts.
Figure 1. Exploded View of Connecting Rod Assembly.
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Pistons and Rings
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Pistons are cast aluminum alloy and are cam ground. They are fitted with two compression and one oil control ring.
Pistons receive force of combustion pressure and transmit it to connecting rod and crankshaft. Escape of
combustion pressure past piston is prevented by piston rings. Fit of piston and rings in sleeve must be close
enough to prevent escape of combustion gases, yet be free enough to keep friction to its working minimum.
The oil control ring provides an even circulation of lubricating oil and therefore, an overall lubrication and cooling
action for piston and crankcase sleeve.
Excess oil is wiped by rings, back down to crankcase.
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