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7.
AUTOMATIC
DECOMPRESSION
SYSTEM
The decompression system operates to release compression
by
lifting up the exhaust valve at
starting.
The release lever mounted on the camshaft has a flyweight at one end and a crescent cam at
the other end. When starting the engine, the crescent cam juts out from the exhaust cam.
The exhaust tappet rides over the crescent cam opening the exhaust valve to release
compression.
CRESCENT
EXHAUST
LEVER
Fig.
64
When the crank speed reaches
a
certain revolution, the flyweight
of
the
release lever moves outward
by the centrifugal force turning the release lever to retract
the
crescent cam. Thus the exhaust
valve closes allowing
a
sufficient compression for
the
engine
to
start
up.
FLYWEIGHT
RELEASE LEVER
CRESCENT
CAM
EXHAUST
CAM
CAMSHAFT
Fig.
65
The
components
of the decompression system
are
different between “D”type and
“B”type
engines,
however the principle
of
operation
is
the same.
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