| 摘要 |
An engine combustion chamber has a protruding wall disposed around a part of each valve seat of either an intake port or an exhaust port. The protruding wall extends in a direction in which a valve for the intake or exhaust port lifts up and down within the combustion chamber and is formed so as to have a jut from a periphery of each valve seat which is set to be less than the larger of a valve lift of the valve of the intake or exhaust port at its top dead center position and a product of a constant and a crank angle from a top dead center of a valve of the other port until the valve of the other port is substantially closed after the top dead center position thereof. A protruding wall gap between inner wall surface of the combustion chamber and an outer periphery of the largest diameter of a valve head of the valve is smaller than the jut, and a valve gap between the outer periphery of the largest diameter of a valve head and an inner periphery of the largest diameter of the combustion chamber is larger than the protruding wall gap.
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