Importance

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Abstract

A compression relief mechanism for a small four-cycle engine to facilitate cranking. The engine has a single cam actuating both the intake and exhaust valves. The cam has a primary cam surface and a boss extending from its side. The exhaust valve cam follower engages only the primary cam surface. The intake valve cam follower has a first cam follower surface engaging only the primary cam surface and a secondary cam engagement surface engaging only the boss to open the intake valve during a predetermined portion of the engine's compression cycle. The opening of the intake valve during the compression cycle provides compression relief facilitating cranking. The secondary cam follower surface may be provided on either the intake or exhaust cam follower to open either the intake or exhaust valve during the compression cycle to provide the desired compression relief during cranking. In an alternate embodiment, the secondary cam surface is displaced by centrifugal force to a location inhibiting the secondary cam engagement surface from engaging the secondary cam surface at normal engine operating speeds.

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First Claim