Patent ID: 8104448

Claim:
A bolt fastening structure with an internal combustion engine, said engine comprising a cylinder block cooperating with a cylinder head to form a combustion chamber, and a crankcase for supporting a crankshaft, wherein said cylinder block, said cylinder head and said crankcase are fastened integrally together by at least one fastening bolt having an external thread formed at an end portion thereof, said bolt fastening structure comprising: said cylinder block having a bolt fitting hole formed therein; a substantially cylindrical boss portion formed on said crankcase on an extension line of said bolt fitting hole; said cylindrical boss portion positioned closer to said cylinder block than a crankshaft rotational support portion of said crankcase; said boss portion having an opening formed therein and extending therethrough and having an internal thread which communicates with said bolt fitting hole; wherein said end portion of said fastening bolt extends through said bolt fitting hole, and is engaged with said internal thread of said boss portion; wherein said crankcase has a hollow recess formed therein between said boss portion and said crankshaft rotational support portion, said hollow recess communicating with said opening of said boss portion at a junction therebetween; wherein an interior portion of said crankcase has a reinforcing rib formed thereon; wherein a tip portion of said external thread of the fastening bolt extends at least to the junction of said hollow recess and said opening in said boss portion; and wherein said reinforcing rib is positioned adjacent the junction of said hollow recess and said opening in said boss portion.