FOUR-STROKE INTERNAL COMBUSTION ENGINE AND EXHAUST VALVE

A cylinder portion 1 configured such that a recess (depression) 14 is formed on an upper edge portion of an inner wall of the cylinder portion to prevent the formation of choke between the inner wall and a side edge 26 of a valve umbrella 22 of an exhaust valve 2, the recess being formed by depressing the inner wall, and the exhaust valve configured such that a cross section of a head portion 26 of the valve umbrella 22 tapers from an outer peripheral edge 25 of the valve umbrella 22 toward a top of the valve umbrella 22 are included.