Four-cycle engine and motorcycle comprising four-cycle engine

摘要

A four-cycle engine of the present invention comprises a gas exhaust outlet that is formed on an upper region of a crankcase to exhaust a gas from the interior of the crankcase to outside; and a rotatable shaft disposed in close proximity to the gas exhaust outlet in the interior of the crankcase. The gas exhaust outlet is configured to open toward a region in the interior of the crankcase, the region extending from a line segment connecting the gas exhaust outlet to a rotational center axis of the shaft, in a rotational direction of the shaft at a cross point where the line segment crosses an outer peripheral surface of the shaft.