Yanmar 2TNV70 Service Manual page 76

4. Disassembly, Inspection and Reassembly of Engines
Point 6
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 TNV series engines as breather system.
The system of model 3TNV76 is shown as a
representative of that breather system in the right
figure. Some of the combustion gas passes through
the clearance between the cylinder and the piston,
piston ring, and flows to the crankcase. This is said
as blowby gas. While it passes into the cylinder
head and the rocker arm cover, the blowby gas
mixes with splash oil, and becomes oil mist-blowby
gas. Next, oil is separated from mist-blowby gas
with passing through the baffle plate inside a rocker
arm cover. And it passes through a diaphragm
assy and a intake manifold, and 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.
[Disassembly]
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 lube oil replacement or lube oil supply
The amount of lube 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 lube oil quantity is beyond the upper limit or an engine is operated beyond
the allowable maximum angle of an engine.
[Reassembly]
Replace the diaphragm with new one, when it is damaged.
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