Abstract: A piston for internal combustion engines, capable of being manufactured easily and improving the durability of a combustion chamber, moved reciprocatingly in a cylinder of an internal combustion engine, and provided in a top surface thereof with a combustion chamber formed by recessing the same top surface, and in an outer circumferential wall of the combustion chamber with a cooling cavity the inner diameter of a lower portion of an inner circumferential surface of which is set smaller than that of an upper portion thereof, wherein a cross-sectionally angular portion defined by an upper edge portion, at which the combustion chamber is opened in the interior of a cylinder, of an inner circumferential surface of the combustion chamber and a piston-top surface is chamfered greatly in conformity with the cross-sectional shape of the upper portion of the inner circumferential surface of the cooling cavity to such an extent that the thickness of an upper portion of an inner circumferential wall of the cooling cavi

Abstract: A connecting rod has at one end thereof two leg portions formed in forked configuration defining therebetween an intermediate groove having a recess of semi-circular cross section on the inside thereof and having oppositely located bolt insertion holes at the leading ends thereof, respectively. In the other side of the intermediate groove is fitted a block having a semi-circular recess defining a crankshaft bearing hole in opposed relationship with said semi-circular recess of the intermediate groove and having a bolt insertion hole formed therethrough and extending coaxially with each of the bolt insertion holes so as to tighten up and fixedly secure the block between the leg portions by a bolt and nut unit.