A piston member for an internal combustion engine of, for example, a motor bicycle is provided with bosses having inner end surfaces opposing to each other into which a piston pin is inserted. A connecting rod has small and large end portions and the small end portion is slidably coupled with the end surfaces when the connecting rod is inserted into the body of the piston member through a cutout portion formed at one end thereof to form a skirt portion. The sizes, dimensions, and structures of the end surfaces of the bosses, the cutout portion, and the associated elements are determined to be suitable for coating thin films of metallic particles on the end surfaces by flame coating means.