Decompressor System; Function Of Decompressor System; Description; Construction - Honda Motorcycle Service Manual

CYLINDER HEAD
DECOMPRESSOR SYSTEM
Description
The decompressor which eases the required starting force and also reduces starting kickback. This system is used on all
1988 4-stroke singles of 2 5 0 cc and larger engines. It is more compact and lighter than previous systems and is
maintenance free. On the XRGOOR, it reduces the required starting force to that of a 2 5 0 cc engine.
Construction
The system uses t w o separate decompressor cams: one is for reducing the necessary kickover force (decompressor cam)
and the other reduces starting kickback (reverse decompressor cam). Both of these decompressor cams slip onto the drive
end of the camshaft. The decompressor cam is loosely keyed onto the camshaft which allows
it
to shift positions as the
engine speed increases (after startup). The reverse decompressor cam rotates on a machined surface on the camshaft but
it
can only rotate in one direction because of a one-way roller bearing.
RIGHT EXHAUST ROCKER ARM
REVERSE DECOMPRESSOR CAM
\
/
CAMSHAFT
E-WAY CLUTCH
DECOMPRESSOR CAM
FUNCTION
Decompressor cam
At TDC (on compression) the right exhaust rocker arm is contacting the normal cam lobe's heel (concentric circle) so that
valve is closed, as would be normal. But the decornpressor cam opens the exhaust valve a slight amount to reduce
kickstarting force. After the engine starts, centrifugal force moves the position of the decompressor cam and it becomes
flush with the normal cam lobe's heel.
RIGHT EXHAUST ROCKER ARM
CAMSHAFT
Moment to start valve lift
(Below 800 rpm)
After engine
is
started
(Above 800 rpm)
Date of Issue: March, 1 9 9 5
0
HONDA MOTOR CO.,LTD.
9-7