Water-cooled two stroke engine having exhaust port timing control valve means

Claim 1

A water-cooled two stroke engine comprising cylinder means having cylinder wall means formed with exhaust port means, piston means provided in said cylinder means for reciprocating movement so that the exhaust port means is cyclically closed by the piston means, said exhaust port means being provided at an upper portion thereof with exhaust port timing control valve means, cooling water jacket means formed in said cylinder means, cooling water passage means having restriction means and leading to said jacket means for providing a supply of cooling water to said jacket means, actuator means for moving the valve means under a low engine speed to a position wherein it covers the upper portion of the exhaust port means so that exhaust port opening timing is retarded, said actuator means comprising pressure responsive movable means, operating pressure chamber means defined at one side of the movable means for applying said movable means with a pressure in said cooling water passage means upstream of the restriction means, and compensating pressure chamber means defined at the opposite side of the movable means for applying the movable means with a pressure in said cooling water passage means downstream of the restriction means, said movable means being connected with said valve means so that the valve means is moved to a position wherein it uncovers the upper portion of the exhaust port means when the movable means is moved under a pressure in the operating pressure chamber means.