Chapter Five
Single-Cylinder Engines
This chapter covers the Yanmar
IGM
and IGMIO sin-
gle-cylinder, diesel engines.
The engine consists
of
a cast-iron cylinder block, con-
taining a full-length waterjacket around the cylinder.
The crankshaft rotates counterclockwise as viewed
from the flywheel. Two main bearings support the crank-
shaft, with the front bearing providing the thrust surfaces.
The crankshaft gear drives the rotor-type oil pump located
in the lower front
of
the engine block.
The camshaft is gear driven and located in the engine
block above the crankshaft. One end
of
the camshaft is
supported by a ball bearing (front), and the other rides di-
rectly in the block (rear). In addition to operating the
valves, the camshaft operates the fuel transfer pump and
has an actuating lobe for the injection pump attached at
the front.
Valve actuation is via mechanical lifters and pushrods
acting on the rocker arms mounted in the cylinder head.
Engine specifications
(Table 1) and tightening torques
(Table 2) are located at the end
of
this chapter.
DIESEL ENGINE FUNDAMENTALS
Diesel engines are compression ignition engines, as op-
posed to gasoline engines, which are identified as spark
ignition engines. The intake, compression, ignition, ex-
pansion and exhaust cycle occur in the same sequence for
compression ignition engines as for spark ignition en-
gines. The major differences are how the fuel is intro-
duced into the combustion chamber and how the ignition
is accomplished.
The principle
of
operation for compression ignition en-
gines is to compress air in the cylinder without fuel; as the
pressure increases, so does the temperature. The tempera-
ture
of
the compressed air is sufficient to ignite the diesel
fuel injected into the cylinder, To achieve the required
high-compression pressure/temperature, diesel engines
have compression ratios between 16:1 and 22: 1. These
high compression ratios raise the cylinder air temperature
to approximately 1000
0
F. Diesel fuel will ignite at ap-
proximately
750
0
F. Therefore, diesel fuel injected into
the cylinder will immediately begin to bum.
A high-pressure fuel delivery system is necessary to in-
ject
fuel into the cylinder. The injector pressure must be
higher than air pressure in the cylinder, and the fuel must
be forced through the small openings in the fuel injector to
properly atomize the fuel. Refer to Chapter Seven for fuel
and governor system operation.
Refer to
Figure 1. During the intake stroke, air is drawn
into the cylinder.
During the compression stroke, the air is compressed to
raise its temperature. The seal between the piston and the
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