d. Compression Ring. As stated in paragraph
3-6b, the purpose of the compression ring is to
hold the pressure from the power stroke in the
combustion chamber. There are many different
cross sectional shapes of piston rings available
The various shapes of rings all serve to preload the
ring so that its lower edge presses against the
cylinder wall. As shown in figure 3-21, this serves
the following functions:
(1) The pressure from the power stroke will
force the upper edge of the ring into contact with
the cylinder wall, forming a good seal.
(2) As the piston moves downward, the
lower edge of the ring scrapes, from the
cylinder walls, any oil that manages to work past
the oil control rings.
(3) On the compression and the exhaust
strokes, the ring will glide over the oil, increas-
ing its life.
e. Heat Dam (Fig. 3-22). There is an addi-
tional groove cut in the piston just above the top
ring groove. The purpose of it is to divert some
of the intense heat that is absorbed by the piston
head away from the top ring. The groove Is
called a heat dam.
Figure 3-18. Piston Ring Types
f. Ring Gap. The split in the piston ring is
In addition to the configurations mentioned previ-
ously, there are some diesel engines that use five
Installing the ring on the piston.
or more piston rings on each piston to control the
higher operating pressures.
Figure 3-19. Configurations of Piston Rings.