Internal combustion engine

An internal combustion engine having a pent roof type combustion chamber configured such that an intake port-side ceiling surface in which an intake port is open in a cylinder head and an exhaust port-side ceiling surface in which an exhaust port is open in the cylinder head are inclined to a plane that is perpendicular to a center axis of a cylinder, wherein

• a housing space is formed in an opening of the exhaust port to the combustion chamber to be more recessed in the cylinder head than the exhaust port-side ceiling surface, wherein a bevel portion of an exhaust valve is placed in the housing space in a valve closed state of the exhaust valve, and a valve contact surface which the bevel portion of the exhaust valve comes in contact with in the valve closed state of the exhaust valve is formed on an inner wall surface of the housing space, wherein
• in a slight lifting state of the exhaust valve that the exhaust valve is lifted up and part of the bevel portion of the exhaust valve is placed in the housing space, the housing space includes an intake side space that is a clearance between the inner wall surface of the housing space and the bevel portion of the exhaust valve and is located on an intake port side, and an exhaust side space that is the clearance and is located on a bore wall surface side of an exhaust port side which is opposite to the intake side space across the bevel portion of the exhaust valve, and
• with regard to an effective passage width of an effective passage that is defined as a linear virtual passage extended from the combustion chamber through the housing space to inside of the exhaust port in a section extended from the intake port side to the bore wall surface side of the exhaust port side, the housing space is formed such that the effective passage width in any location in the intake side space is made smaller than the effective passage width in a corresponding location in the exhaust side space in the slight lifting state of the exhaust valve.