To provide a crank pin bolt enabling measuring/managing by a ultrasound axial force meter while preventing galling of a screw portion tip end and ensuring an effect of reducing a stress.
In the crank bolt 21 fastening a divided large end portion of a connecting rod to a crank pin, a recessed portion 37 is formed on a tip end surface 35, and a flat bottom portion 41 in a direction orthgonal to an axis line 39 is provided on the recessed portion 37. The crank pin bolt may make an inner surface of the recessed portion to be a taper surface gradually decreased in a diameter toward the bottom portion. In this case, preferably, the recessed portion is 20 to 60 % of a bolt outer diameter in diameter of the bottom portion, and 20 to 120° in taper angle.
KOJIMA HIDEKI
ISHII MOTOKI
WATANABE KOICHI
