Patent ID: 7389763

Claim:
A cylinder block integrated with a crankcase used for a single-cylinder small internal combustion engine, a cylinder part and a crankcase part formed into a box-like shape being cast in one piece, a crankcase cover being fixed to the crankcase part to cover an opening on a side in an anteroposterior direction thereof, a crankshaft bearing boss having a crankshaft bearing hole being provided near at a central part of a back wall of said crankcase part to protrude to both inner and outer sides of said back wall for supporting an end sides of a crankshaft, wherein an inner peripheral rib is formed along the corner where said back wall of said crankcase part connects to a peripheral wall extending from the periphery of said back wall and extends from the periphery of said back wall to form said box-like shaped crankcase part, and wherein said inner peripheral rib heaves inward from said corner part.