70
CHAPTER
FIVE
Open
-
chamber
Fuel injector
chamber
cylinder must not permit compression leakage, which
could lower the temperature of the compressed air. Also,
the cylinder must not contain fuel that could ignite prema
-
turely during compression.
Near the end of the compression stroke, fuel is injected
into the cylinder and ignited by compressed air. Fuel in
-
jection continues during several degrees of crankshaft ro
-
tation, depending upon desired speed and load. Expansion
of the air caused by the burning fuel pushes the piston
down on the expansion (power) stroke.
The exhaust valve opens just before the piston reaches
the bottom of travel. The exhaust valve remains open as
the piston moves upward pushing burned (exhausted) gas
-
ses from the cylinder.
Different combustion chamber designs may be used on
diesel engines to accomodate specific engine operating
criteria. An open combustion chamber (direct injection)
design is illustrated in Figure 2. The fuel and air are con
-
fined to one area. Usually the piston crown is concave to
form the combustion chamber and provide turbulence re
-
quired for mixing the fuel with the compressed air. The
shape of the combustion chamber and the shape of the in
-
jection spray pattern are matched so that fuel will be dis
-
tributed evenly throughout the chamber.
The Yanmar engines covered in this manual are
equipped with a precombustion chamber for each cylinder
(Figure 2). The precombustion chamber increases com
-
bustion efficiency, which produces greater power with re
-
duced emmissions. Combustion first occurs in the
precombustion chamber when hot, compressed air enters
the precombustion chamber just as fuel is injected. Com
-
bustion continues as the fuel and air are mixed and forced
from the precombustion chamber into the engine cylinder.
Additional mixing and ignition are completed in the cylin
-
der.
ENGINE SERIAL NUMBER AND CODE
The engine serial number and model designation are lo
-
cated on a plate attached to the rocker cover (Figure
3).
The engine serial number is also stamped on the side of
the cylinder block (Figure
4).
Have the engine model number and serial number avail
-
able when ordering parts. Record the engine model and
serial numbers and store them for future reference in case
the identification plate on the engine is defaced or lost.
REPLACEMENT PARTS
When installing new parts on the engine, make sure the
part is designed for use on a marine engine. Automotive
and marine engine parts may look similar; however, auto
-
motive parts may not be capable of operating in a harsh
marine environment.
Use only Yanmar parts or parts approved for use on ma
-
rine engines.
ENGINE REMOVAL PRECAUTIONS
Some service procedures can be performed with the en
-
gine in the boat; others require removal. The boat design
and service procedure to be performed determines
whether the engine must be removed.
WARNING
The engine is heavy, awkward to handle and
has sharp edges.
It
may shift or drop sud-
denly during removal. Toprevent serious in-
jury, always
observe the following
precautions.
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