Internal Combustion Engine

摘要

To provide structure for avoiding the concentration of stress caused in the bolt hole in a circumference of the end of the bolt in a fastened part and to lighten the crankcase (2) in an internal combustion engine (1) provided with a fastening bolt for fastening upper and lower crankcases (2B) in a circumference of a crankshaft (11) and a bolt hole which is formed in the crankcase (2) and into which the fastening bolt is inserted and tightened. An opening is formed at an upper end of the bolt hole in the upper crankcase (2A), the end of the bolt hole is made to communicate with the opening, and the end of the fastening bolt is protruded into the opening in fitting the bolt.