PURPOSE: To prevent the break and lack as well as fretting corrosion on the joint surfaces for preventing the rattling of a crankpin and the deformation and breakage of a bolt, by applying the plating of a high hardness on the joint surfaces between the body of a connecting rod and the cap.

CONSTITUTION: A piston 1 is connected to the crankpin 4 of a crankshaft 3 via a connecting rod 2. The large end part 5 of the connecting rod 2 is partitioned into a connecting-rod body 6 and a cap 7, and joint surfaces 8 and 9 are provided. The connecting-rod body 6 and the cap 7, after the crankpin 4 has been placed between them via a pair of plain bearings 12, are fitted to the crank-shaft 3 by means of bolts 15 and nuts 16. On the joint surfaces 8 of the connecting rod 2 and the joint surfaces 9 of the cap 7, plating having a hardness higher than that of titanium alloy is applied.