| 摘要 |
A main bearing case has a bearing holder for holding a bearing so as to support a crankshaft, and a crankcase mounting section at which it is joined to a crankcase. Rib walls are provided so as to surround the bearing holder between the bearing holder and the crankcase mounting section. The rib walls are formed in a side of the crankcase, and in a neighborhood of each inner side face of the bearing holder and the crankcase mounting section. These rib walls receive a force exerted in a radial direction from the crankshaft. Thereby, an improvement of rigidity of the main bearing case can be achieved, and also the lubrication to a valve-operating system can be always ensured by preventing an oil surface from lowering even when an engine is located with inclination.
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