| 摘要 |
PROBLEM TO BE SOLVED: To enhance the durability of a crank shaft by narrowing a space between a first and a second bearing part, which support both the end parts of the crank shaft without interfering with a valve system mechanism, and make assemblage excellent by assembling the valve system mechanism after a first and a second case half-body composed of a crank case have been combined with each other. SOLUTION: A crank case 3 is formed out of a first and a second case half-body 31 and 32, which are mutually combined with each other at a split surface P obliquely intersected with the axial lines of a first and a second bearing part 131 and 132. A cylinder barrel 5 and the first bearing part 131 are formed integrally with the first case half-body 31 so as to be formed into an engine block 1a, and the second bearing part 132 is formed integrally with the second case half-body 32, and a side cover 14 pertitioning a valve system chamber 15 for housing a valve system mechanism 19, is joined with the outer side surface of the engine block 1a.
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