| 摘要 |
A four-stroke engine includes a case which is comprised of a first case half and a second case half connected with each other at a parting plane which goes through centerline of a crankshaft and is perpendicular to centerline of a cylinder. A first bearing seat is divided into a first upper bearing seat half and a first lower bearing seat at the parting plane. A second bearing seat is divided into a second upper bearing seat half and a second upper bearing seat half at the parting plane. The first upper bearing scat half and the second upper bearing scat half are integrally molded on the first case half, and the first lower bearing seat half and the second lower bearing seat half are integrally molded on the second case half. An outer side surface of the first case half and a side cover form a valve-operating chamber for accommodating a valve-operating mechanism.
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