Subaru Robin Power Products EH12-2, EH17-2, EH25-2 manual Automatic Decompression System

7.AUTOMATIC DECOMPRESSION SYSTEM

EH12-2, 17-2, 25-2 engines are employing the automatic decompression systemas a standard feature. This enables easy and light startof the engine. Theautomaticdecompressionsystemreleasesthecompression of theengine by liftinguptheexhaust 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 type “B” engines, however, the principle 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 crescent cam projects the camshaft cam profile and lifts up the tappet because the gravity force on the weightis larger than the centrifugal forceon the weight.

iTAPPET,I

LEVER

CRESCENT

EXHAUST

Fig. 7-1

When the crank speed reaches up to a certain revolution, the crescent 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.andis shifted to the position shown in the illustration.

FLYWEIGHT

LEVER

CRESCENT CAM	EXHAUST-YCAM-T3
EXHAUST CAM		,”-
	CAMSHAFT
	Fig. 7-2

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