| 摘要 |
An internal combustion engine in a power unit includes an oil pump that rotates by a transmission mechanism with an endless chain, and a crankcase with an opening formed by protruding walls of side walls of the crankcase in an axial direction. A drive sprocket is fitted to a main shaft of a gear transmission and a driven sprocket is fitted to a shaft end of a drive shaft of an oil pump. When viewed sideways, the protruding walls and mating faces have overlapping parts that partially overlap the driven sprocket. On the other hand, all the shaft end and the remainder of the driven sprocket are exposed inside the opening when the cover is removed. The resulting configuration improves the working efficiency in fitting an oil pump into the crankcase without reducing the rigidity of the crankcase.
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