| 摘要 |
PROBLEM TO BE SOLVED: To ensure the sealing property of a connecting surface, and improve supporting rigidity by setting dividing surfaces of first and second crankcases in parallel with an axis of a crankshaft, and rotatably supporting at least two positions mutually holding a crank pin of the crankshaft on the first case side. SOLUTION: A crank case 33 for housing a crankshaft 36 is formed by mutually connecting a lower case 37 connected to a cylinder block 30 and an upper case 38 formed at a rear part of a down frame to each other avoiding direct connection to a cylinder block 30 of the upper case 38. A dividing surface 39 of the lower and upper cases 37, 38 is set in parallel with an axis of a cylinder bore 31 and an axis of the crankshaft 36. The crankshaft 36 is housed on the lower case 37 side in both cases 37, 38 for composing the crankcase 33, and at least two positions mutually holding crankpin 36a of the crankshaft 36 are rotatably supported at the lower case 37.
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