Engine
SHOP MANUAL
Ch 1 page 101
Piston rings
For the piston to travel freely, a gap is required between the
piston and cylinder liner.
The piston therefore has two compression rings which seal this
gap and conduct the heat from the piston.
The upper of these rings is exposed to higher pres sure than the
intermediate ring and is therefore wedge-shaped, a “keystone”
ring, which increases the force pressing it against the cylinder
wall.
Since the greatest stress is on the upper piston ring groove,
and also to reduce wear, a reinforcement of cast iron is incorpo-
rated in the piston.
The bottom piston ring, the oil scraper ring, pre vents oil from
the crankcase from finding its way up to the combustion cham-
ber.
In the oil scraper ring is a coil spring which presses it against
the cylinder wall.
The design and quality of the pistons and piston rings are ex-
tremely important for the reliability and lubrication of the engine
as well as oil and fuel consumption.
Turn the piston rings so that the gaps are distributed around the
piston.
The bowl-shaped combustion chamber in the piston crown
has a protuberance in the centre. The design of this pro-
tuberance ensures that the fuel injected at the end of the
compression stroke is quickly mixed with the air in the com-
bustion chamber.
Figure 191
Figure 192
Figure 193
Figure 194
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