WM 130/170/270 Theory of Operation
wc_tx000378gb.fm 33
Decompression system
The automatic decompression system is
mounted on the camshaft. It opens the
exhaust valve before the compression top,
thereby alleviating the compression pressure
and reducing the force required to pull the
recoil starter.
During engine operation, the decompression
system is overpowered by centrifugal force
and compression is fully utilized to produce
power.
Reference: return spring (a), exhaust valve
rocker arm (b), camshaft (c).
Piston rings
The piston rings are made of special cast iron.
The profile of the top ring (a) is a barrel face,
that of the second ring (b) is a tapered face.
There are two types of oil rings depending on
specification: cutter ring with oil expander (c
1
)
or a three-piece type (c
2
).
Component Illustration Component Description
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