Patent ID: 8800509

Claim:
A scavenging passage structure for a two-stroke engine, having a scavenging passage communicating a scavenging port provided in a cylinder with a crank chamber formed inside a crankcase, said scavenging passage being formed to extend through respective fastening surfaces of said cylinder and said crankcase, wherein said crankcase comprises a front crankcase portion and a rear crankcase portion divided along a front and back split surface, said front and baqck split surface being orthogonal to a crankshaft axis, the scavenging passage structure further having: a cover member fastened inside each of said front crankcase portion and said rear crankcase portion with fastening members so as to be in contact with a first inner wall surface of said crankcase as viewed in a direction orthogonal to said crankshaft axis; and a groove recessed into a direction of said crankshaft axis in a contact surface between said first inner wall surface of said crankcase and said cover member, and forming part of said scavenging passage connecting to said crank chamber and to an upper face of said crankcase, wherein said cover member is fitted between two second inner wall surfaces which are opposed to each other at respective ends of said first inner wall surface.