PURPOSE: To prevent the inflow of oil into a cylinder head by providing a small hole which communicates with an oil pan, a crank case, and the cylinder head at the location lower than the cylinder head of the tilted up engine in the front part of the cylinder head.

CONSTITUTION: The oil, which is supplied to the engine so as to lubricate it by a sucking pipe 63, is stored in the recessed part of the lower part of the crank case. Thereafter the oil is returned to the oil pan 45 through the small hole 48. The small hole 48 is provided at the location which is lower than the cylinder head, when the tilt up is performed in front of the cylinder head. In this constitution, the oil does not enter the cylinder head at the time of tilt up, and the trouble in the valve gear systems and the like and oil lowering and the like can be prevented.