WM 130/170/270 Repair Sub Systems
wc_tx000382gb.fm 79
10. Sub Systems
10.1 Automatic Decompression System
See Graphic: wc_gr001827
WM-series engines employ an automatic decompression system as a
standard feature. This feature enables easy starting of the engine with
lighter recoil pull. The automatic decompression system releases the
compression of the engine by lifting up the exhaust valve at cranking
speed.
At the end of the compression process, the release lever (a) lifts up the
exhaust rocker arm (b) which in turn opens the exhaust valve slightly
to release the compression. The release lever has a flyweight on one
end and a crescent cam (c) on the other. When the engine is cranked,
the crescent cam projects above the cam profile and lifts up the rocker
arm because the force of the return spring on the weight is larger than
the centrifugal force on the weight.
Reference: Intake rocker arm (d); cam (e); camshaft (f). Cranking (A);
running (B).
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