| 摘要 |
PROBLEM TO BE SOLVED: To provide a four-stroke engine having suitably reduced pumping loss by enlarging a communication port between a crank chamber and another space. SOLUTION: The four-stroke engine comprises a bearing storage part 24 provided on a crank chamber wall portion 31L forming the crank chamber storing a crank shaft for storing a bearing turnably journaling the crank shaft and the communication port 60 provided in the crank chamber wall portion 31L of the crank chamber in the radial direction of the bearing for communicating a cam chain chamber with the crank chamber adjacent thereto in the axial direction of the crank shaft. At the edge of the communication port 60 on the side of the bearing, a bent portion 62 is provided corresponding to the shape of an inner peripheral face 24a of the bearing storage part 24. COPYRIGHT: (C)2006,JPO&NCIPI
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