Yanmar 3JH4E, Service Manual

Page: 263 / 350

7. Intake and exhaust system
243
7.1.4 Breather system (A reductor to
intake air system of blowby gas)
Emitting blowby gas is harmful to natural
environment. Therefore blowby gas reductor is
adopted to 3JH4 and 4JH4 naturally-aspirated
engines as breather system.
Some of the combustion gas passes through the
clearance between cylinder and piston, and flows
to the crankcase. This is said as blowby gas. While
it passes into cylinder head and rocker arm cover,
the blowby gas mixes with splash oil, and
becomes oil mist-blowby gas. The gas passes
through the baffle plate inside a rocker arm cover.
And it passes through a diaphragm assy, and
reaches a intake silencer. The gas is reduced in
the combustion chamber.
Pressure inside a crankcase is controlled by the
function of the diaphragm assy, and suitable
amount of blowby gas is reduced in intake air
system.
[Disassemble]
When a rocker arm cover is taken off, check
whether oil or the like enter the diaphragm space
from a small hole on the side of a diaphragm
cover or not without disassembling the
diaphragm.
[NOTICE]
1) When a diaphragm is damaged, pressure
control inside the crankcase becomes
insufficient, and troubles occur. When the
internal pressure of the crankcase decreases
too much due to the damage of a spring,
much blowby gas containing oil is reduced in
intake air system, and it may cause the
combustion defect by the early dirt of the
intake valve or the urgent rotation of the
engine by the oil burning.
When pressure progresses in the crank case
too much due to the wrong operation of the
diaphragm and so on, it is considered that oil
leakage from the joint of a oil pan, a oil seal
and so on will occur. When a diaphragm is
damaged, blowby is discharged from the
breathing hole on the side of diaphragm
cover, and not reduced in the intake
manifold. Therefore, be careful of the
diaphragm trouble.
2) At lubricating oil replacement or lube oil
supply
The amount of lubricating oil isn't to be
beyond the standard upper limit (in the
engine horizontality, the upper limit mark of
the dip stick). Since the blowby gas reductor
is adopted, be careful that the amount of oil
mist may be inducted in the combustion
chamber and the oil hammer sometimes may
occur, when the lubricating oil quantity is
beyond the upper limit or an engine is
operated beyond the allowable maximum
angle of an engine.
Center plate
Spring
Diaphragm
Diaphragm cover
Rocker arm cover
Breather
baffle
Baffle plate
Intake silencer
Breather pipe
010635-00E
Blowby gas flow
Blowby gas flow
to diaphragm
space
Diaphragm part
Baffle plate
Rocker arm
cover
Center plate
Diaphragm cover
Spring Diaphragm
010646-00SE
Blowby gas flow