Automatic Decompression System - Subaru ER12 Service Manual

10. AUTOMATIC DECOMPRESSION SYSTEM

10-1 FUNCTIONS AND CONSTRUCTION
EX series engines employ an automatic decompression system as a standard feature . This 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 . The following is the explanation of the function .
At the end of the compression process, the release lever lifts up the rocker arm (exhaust) which in turn
opens up the exhaust valve slightly to release the compression .
The release lever has a flyweight on its end and another end of the lever is a crescent cam .
When the engine is cranked, the crescent cam projects above the cam profile and lifts up the rocker arm
(exhaust) because the force of the return spring on the weight is larger than the centrifugal force on the
weight .
ROCKER ARM
(EXHAUST)
ROCKER ARM
(INTAKE)
CAM
When the cranking speed reaches a specified r .p .m ., the crescent cam is retracted under the cam profile
because the centrifugal force applied to the flyweight becomes larger than the force of the return spring on
the weight and thus it is shifted to the position shown in the illustration below .
ROCKER ARM
(EXHAUST)
ROCKER ARM
(INTAKE)
12-2 INSPECTION
When assembling the release lever, make sure that it works smoothly .
RELEASE LEVER
CRESCENT CAM
CAM A
CRESCENT CAM
RELEASE LEVER
A
DETAIL
RELEASE LEVER
RELEASE LEVER
DETAIL
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ROCKER ARM (EXHAUST)
CAMSHAFT
A
ROCKER ARM (EXHAUST)
CAMSHAFT
A