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7. AUTOMATIC DECOMPRESSION SYSTEM

EH36, 41 engines are employing the automatic decompression system as a standard feature.

This enables easy and light start of the engine.

The automatic decompression system releases the compression of the engine by lifting up the exhaust

valve at the cranking. Following are the explanation using type “D” engine as a sample how the system

works. The components of the systems are different for the type “D” and “B” engines, however, the

pinciple of the function is same.

At the end of the compression process, the release lever lifts up the tappet which in turns 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 cresent cam projects the camshaft cam profile and lifts up the tappet

because the gravity force on the weight is larger than the centrifugal force on the weight.

When the crank speed reaches up to a certain revolution, the cresent cam is retracted into the camshaft

cam profile because the centrifugal force applied onto the flyweight becomes larger than the gravity force

and the weight and is shifted to the position shown in the illustration.

FLYWEIGHT

TAPPET

CRESCENT CAM

EXHAUST CAM

ROTATION

CAMSHAFT

RELEASE LEVER

Fig. 7-1