A cover of an internal combustion engine includes a cover body to be mounted to a crankcase of the internal combustion engine. The cover body includes a through hole, a protruding part, and a plurality of first recessed grooves. The through hole is to support a shaft rotatably. The protruding part is provided above the through hole in an upward direction of the internal combustion engine and protrudes toward an inside of the cover body facing the crankcase. The protruding part includes a first upper part and a first lower part in the upward direction on an inner surface of the protruding part facing the crankcase. The plurality of first recessed grooves extend radially from the through hole so as to connect the upper part and the lower part of the protruding part.

An oil passage structure of a dry sump engine includes an oil recovery passage, at least one first communicating hole, and a first oil suction passage. The oil recovery passage extends in a direction in which a cylinder bank extends and is disposed so that at least part of the oil recovery passage is located outward of an external lower end portion of a valve gear chamber of a cylinder head along a junction between a side wall portion of the cylinder head and a bottom surface of the valve gear chamber in a state where the dry sump engine is mounted on a vehicle in an inclined manner. The at least one first communicating hole is provided in the side wall portion so as to connect the valve gear chamber of the cylinder head and the oil recovery passage.

An engine assembly includes a small air-cooled engine and a dry sump lubrication system including an external oil reservoir, wherein the dry sump lubrication system has an overall oil capacity that provides at least five hundred hours of engine oil life.

A dry sump engine having a simple structure to certainly prevent a pressure rise in an oil tank. In the dry sump engine, a solenoid valve is arranged between the oil tank and a gas receiving section. A controller comprises: a low-pressure determiner that determines whether a pressure in the oil tank is lower than a first reference pressure level; a condition determiner that determines a satisfaction of a predetermined condition; and an open controller that opens the solenoid valve when the internal pressure of the oil tank is lower than the first reference pressure level, or when the predetermined condition is satisfied.