Patent ID: 7284529

Claim:
An engine comprising: a crank case ( 1 ) provided with a lower opening portion ( 2 ), the crank case being covered from below with an oil pan ( 3 ); and a crank shaft ( 4 ) positioned within the crank case and extending in front and rear directions, the crank case being provided with a pair of left and right oil passages ( 7 ) and ( 8 ) which respectively extend in the front and rear directions along left and right lateral walls ( 5 ) and ( 6 ) of the crank case ( 1 ); wherein the left and right lateral walls ( 5 ) and ( 6 ) of the crank case ( 1 ) are provided with left and right ribs ( 12 ) and ( 13 ) which respectively extend in the front and rear directions, the left and right ribs being raised inwardly from the left and right lateral walls ( 5 ) and ( 6 ) of the crank case ( 1 ), the left and right ribs ( 12 ) and ( 13 ) being positioned at the lower opening portion ( 2 ) at a lower end of the crank case ( 1 ) and include therein, the left and right oil passages ( 7 ) and ( 8 ).