7.
AUTOMATIC
DECOMPRESSION SYSTEM
EH12,
17,
25
engines are employing the automatic decompression system as a standard feature.
The automatic decompression system releases the compression of the engine
by
lifting up the exhaust
valve at the cranking. Following are the explanation using type
“D”
engine
as
a sample how the system
works. The components
of
the
systems are different for the type
“D”
and type
“B”
engines, however, the
principle
of
the function
is
same.
’
This enables easy and
light
start
of
the engine.
At the
end
of
the
compression process,
the
release
lever
lifts
up
the tappet which
in
turns
opens up the
exhaust valve
slightly
to release the compression. The release lever
has
a flyweght
on
its
end and another
end
of
the
lever
is
a crescent cam.
When the engine
is
cranked, the crescent cam projects the camshaft cam profile and
lifts
up the tappet
because the gravity force
on
the weight
is
larger than the centrifugal force on the weight.
CRESCENT
EXHAUST
LEVER
‘7
CAMSHAFT
Fig.
7-1
When the
crank
speed reaches
up
to
a
certain revolution, the crescent cam
is
retracted into the camshaft
cam
profile because the centrifugal force applied onto the flyweight becomes larger than the
gravity
force
and
the weight and
is
shifted to the position shown
in
the illustration.
FLYWEIGHT
LEVER
Fig.
7-2
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45
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