Two-cycle engine

Claim 1

A two-cycle engine comprising: (a) a cylinder block including a cylinder having an axis, and an exhaust port formed in a peripheral side surface of said cylinder, said exhaust port having upper and lower edges spaced from each other along the axis of said cylinder, said cylinder block having an exhaust passage communicating with said exhaust port, a recess being formed in said cylinder block and opening to said exhaust passage, said recess having a first end face disposed adjacent to said upper edge of said exhaust port; (b) a piston received in said cylinder for reciprocal movement therealong so as to close and open said exhaust port; and (c) a port timing control means for varying a timing of the opening of said exhaust port by said piston, said port timing control means comprising a valve member having a second end face curved along said peripheral side surface, said valve member being angularly movable in a direction of the axis of said cylinder between an extended position where said valve member is extended into said exhaust passage with said second end face closing an upper portion of said exhaust port and a retracted position where said valve member is retracted from said exhaust passage and fully received in said recess with said second end face opening said upper portion of said exhaust port, said second end face being complementary in shape to said first end face, said valve member having a wedge-shaped projection formed on a lower portion of said second end face and reducing in thickness progressively toward said cylinder, so that said second end face has an upper surface and a lower surface extending from a lower end of said upper surface in slanting relation thereto toward said cylinder, said upper surface being held in sliding and sealing contact with an upper portion of said first end face complementary in shape to said upper surface of said second end face.