STRUCTURE FOR CRANKCASE

An object of the present invention is to propose a structure of a crankcase capable of coping with increased combustion pressure inside a cylinder of an engine by a simple and inexpensive means for suppressing the deformation at a middle section between adjacent fastening bolts in a direction connecting the centers of adjacent cylinders. The structure of the crankcase which has a plurality of cylinders and a plurality of bolts arranged on both sides of each of the cylinders for fastening the cylinders to a cylinder head, the structure of the crankcase comprises a reinforcing rib 6 formed on an outer wall of the cylinder at a middle section between the adjacent fastening bolts 3 in a direction 20 connecting centers of the adjacent cylinders, the reinforcing rib extending downward continuously from the cylinder top plate in a direction parallel to a center line 4a of the cylinder.