| 摘要 |
The engine has a single cam (106) actuating both the intake and exhaust valves (50, 56). The cam has a primary cam surface (110) and a boss (112) extending from its side. An exhaust valve cam follower (90) engages only the primary cam surface. The intake valve cam follower (86, 114) has a first cam follower surface (124) engaging only the primary cam surface and a secondary cam engagement surface (128) engaging only the boss to open the intake valve during a predetermined portion of the engine's compression cycle to provide compression relief facilitating cranking. The secondary cam follower surface may be provided on the exhaust cam follower instead. In an alternate embodiment, the secondary cam surface (212) 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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