| 摘要 |
A four-stroke cycle engine particularly for a working machine including a crank chamber structure comprises a crank chamber body defining a crank chamber in which a lubrication oil is sealed and in which a crank shaft mounting a counter-weight member thereon is rotatably supported, a rib member provided for the crank chamber body projecting in the crank chamber near the counter-weight member and a cover member for covering the crank chamber body. The cover member is provided with a projecting portion substantially facing a side surface of the counter-weight member and projecting deeply inside the crank chamber. The cover member comprises a main cover body secured to the crank chamber body, a side wall portion having a rotation surface of substantially a fallen trapezoidal shape in section, and a circular wall portion formed integrally with the side wall portion, the side wall portion and the circular wall portion constituting the projecting portion projecting inside the crank chamber as an integrated structure. The projecting portion is disposed substantially concentrically with a rotation axis of the crank shaft.
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