34
fig. 3. 59 Piston
CD Piston head
® Lands
@ Piston skirt
© Slipper
fig. 3. 60 Piston ring sectional view
CD Top ring
® Oil ring
@ Second ring
3 ENGINE
point toward the point of weaker pressure, which,
is before top-dead-center. By so doing, the piston
can escape the high pressure and makes it possible
to eliminate the piston slap.
Piston is made with a dome head to give it
extremely high strength. Further, this will enable
higher compression ratio and limit overheat ing of the
piston. The skirt of the piston is designed slippered
on the side where no side load is app lied. This
is to reduce weight and also to minimize the fri-
ctional area.
Piston pin is of a floating type and is set in
place by ring clips. The bottom side of the piston
head is provided with reinforcement
fins for added
strength as well as for a better cooling affect.
Oil drain holes are mode just below the oil ring
groove to allow the oil to flow bock into the
crankcase.
(Fig. 3. 59)
V. Piston Ring Construction
The piston rings performs a vital function of form-
ing a seal between the piston and cylinder; controlling
the lubrication of the cylinder wall and dissipating
the heat of the piston produced by the combustion.
The condition of the piston will hove considerable
effect on the power developed by the engine.
Rings are mode of special cast iron for greater
strength, wear and heat resistance, and possesses
good heat conducting qualities. Further, the cylinder
wall contacting surface of the top and oil rings ore
given a hard chrome plated surface and
11nished by
wet honing for greater wear resistance and good
sealing.
To prevent ring flutter, the rings ore made thinner
and greater in depth to increase the pressure against
the cylinder wall. Further,
the top and the second
rings are mode at a slight toper were it contacts
the cylinder wa ll so that the wear-in time is hastened.
Oil ring grooves and the bottom of the second
rings are scalloped to improve oil control and pre-
venting oil entry into the combustion chamber which
would cause carboning up of the spark plugs, piston,
rings and etc.
Whe n assembling the rings, make certain that the
ring manufacturer's mark adjacent to the ring gap
is on the top and the gaps for the three rings should
be spaced equally apart.
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