Chapter
Six
Multicylinder Engines
This chapter covers the Yanmar 2GM, 2GM20, 3GM,
3GM30, 3HM and 3HM35 multicylinder, marine diesel
engines.
The engine consists of a cast iron cylinder block with
full
-
length water jackets around each cylinder. 2GM,
3GM, 3HM (including
F
and
D
series) engines have re
-
placeable cast iron cylinder liners.
Crankshaft rotation is counterclockwise as viewed from
the flywheel. On two cylinder engines, the crankshaft op
-
erates in three main bearings, with the center bearing pro
-
viding the thrust surfaces. On three cylinder engines, the
crankshaft operates in four main bearings, with the third
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 block
above the crankshaft. One end of the camshaft is sup
-
ported by a ball bearing (front) and the other rides directly
in the block (rear).
On three cylinder engines, the camshaft is equipped
with two additional bearings. 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.
The cylinders on 2GM and
2GM20 engines are num
-
bered from rear (flywheel) to front (timing gearcase): 1
-
2.
The cylinders on
3GM, 3GM30,3HM and 3HM35 en
-
gines are numbered from rear (flywheel) to front (timing
gearcase): 1
-
2
-
3. The firing order is 1
-
2
-
3.
Engine specifications (Tables 1
-
3) and tightening
torques (Table
4)
are located at the end of this chapter.
Refer to Chapter Five for diesel engine fundamentals.
NOTE
Except where specified, F and
D
series en
-
gines are included when a basic model num
-
ber is speciJied. For example, ifmodel
3GM
is called out in a procedure, the procedure
also applies to
3GMD
and
3GMF
ENGINE SERIAL NUMBER AND CODE
The engine serial number and model designation plate
is attached to the timing
gearcase (Figure 1). The engine
serial number is also stamped on the side of the cylinder
block (Figure
2).
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