PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 1/TASK 1
(4) Compression Ring. As stated in paragraph 3b(2) (a) on page 21, the purpose
of the compression ring is to maintain a gastight seal between piston and cylinder,
and to hold the pressure from the power stroke in the combustion chamber. There
are many different cross sectional shapes of piston rings available (figure 21).
FIGURE 21. TYPES OF COMPRESSION RINGS.
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 22 on the following page,
this serves the following functions:
(a) The pressure from the power stroke will force the upper edge of the ring
into contact with the cylinder wall, forming a good seal.
(b) As the piston moves downward, the lower edge of the ring scrapes any oil
that works past the oil control rings from the cylinder walls.
(c) On the compression and the exhaust strokes, the ring will glide over the
oil, increasing the ring's life.