Internal combustion engine

An internal combustion engine, comprising:

• an intake port and an exhaust port which communicates communicate with a combustion chamber;
• an intake valve including an intake valve shaft and an intake valve head, the intake valve head being arranged at an end of the intake valve shaft and opening and closing the intake port;
• and
• an exhaust valve including an exhaust valve shaft and an exhaust valve head, the exhaust valve head being arranged at an end of the exhaust valve shaft and opening and closing the exhaust port,
• wherein the intake valve has a surface including an intake-valve-head front surface exposed in the combustion chamber when the intake valve is closed and an intake-valve-head back surface exposed in the intake port when the intake valve is closed,
• wherein the exhaust valve has a surface including an exhaust-valve-head front surface exposed in the combustion chamber when the exhaust valve is closed and an exhaust-valve-head back surface exposed in the exhaust port when the exhaust valve is closed,
• wherein an arithmetic mean roughness of the whole exhaust-valve-head back surface is greater than an arithmetic mean roughness of each of the whole intake-valve-head front surface, the whole intake-valve-head back surface and the whole exhaust-valve-head front surface,
• wherein the arithmetic mean roughness of the whole exhaust-valve-head back surface is greater than 0.5 μm, and
• wherein the arithmetic mean roughness of each of the whole intake-valve-head front surface, the whole intake-valve-head back surface and the whole exhaust-valve-head front surface is equal to or less than 0.5 μm.