Patent ID: 7694661

Claim:
A crankcase for a multiple-cylinder four-cycle engine, comprising: an upper crankcase and a lower crankcase which are joined to each other at a joint surface, the upper crankcase having a cylinder block at an opposite side of the joint surface and an upper transmission case at a rear portion thereof, the lower crankcase having a lower transmission case at a rear portion thereof; a separating wall which is integrally cast with the upper crankcase and the lower crankcase to extend from the joint surface toward the opposite side of the joint surface and is configured to define crank chambers corresponding to adjacent cylinders; and a crank journal bearing hole which is formed on the separating wall such that an axis of the bearing hole passes through the joint surface of the upper crankcase and the lower crankcase and is configured to support a crankshaft; wherein at least the separating wall formed in the upper crankcase has a thickness that increases from the joint surface of the crankcase to a region near a deepest portion of the crank journal bearing hole and decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase.