AIR-COOLED ENGINE, CYLINDER BODY MEMBER FOR AIR-COOLED ENGINE, AND AIR-COOLED ENGINE MOUNTED VEHICLE

摘要

PROBLEM TO BE SOLVED: To provide an air-cooled engine capable of improving cooling efficiency, in particular, cooling efficiency in initial sliding of a piston portion.SOLUTION: In an air-cooled engine including a piston portion, and a cylinder body portion having a sliding face on which the piston portion is slid, the cylinder body portion includes a heat radiation portion disposed on an outer surface of the cylinder body portion, and composed of metal including Al, and at least an inner peripheral portion including the sliding face, of the cylinder body portion is composed of Al alloy having a Si content of 16 mass % or more. A plurality of substantially parallel linear grooves are formed on the sliding face, primary-crystal grains having an average crystal grain diameter of 8 μm or more than 50 μm or less are exposed to be kept into contact with the piston portion, an Al contact portion which is formed between the plurality of linear grooves and of which an Al alloy base material is kept into contact with the piston portion, is exposed to the sliding face between two primary-crystal Si crystal grains adjacent to each other, and Al in the cylinder body portion is physically continued from the Al contact portion to the heat radiation portion.SELECTED DRAWING: Figure 4