| 摘要 |
PURPOSE:To simplify the positioning of the valve, in a mechanism which the opening upper portion of an exhaust passage formed in a cylinder is closed by a plate-like valve, by forming a restriction surface restricting the axial position of the valve on the inner wall surface of the exhaust passage which supports one end of the support axis of the valve. CONSTITUTION:A depression 15 is formed on the upper portion of an exhaust passage 3 and on the slightly downstream side of an exhaust port 4, and a plate-like valve 14 which is oscillatable around an axis 17 is received in this depression 15. The axis 17 is connected with a drive source driving corresponding to the revolution speed of an engine via a valve driving mechanism 8. And the insert hole 16 of the axis 17 is formed in the depression 15 orthogonally to the center line of a cylinder 2, and the reduced diameter portion 16a of its tip is formed in one side wall of the exhaust passage 3. Then, the tip portion 17a of the axis 17 is formed in a reduced diameter corresponding to the insert hole 16, the enlarged diameter base portion 17b of the axis 17 is inserted into the enlarged diameter penetrating hole portion 16b of the axis insert hole 16, and the tip portion 17a of the axis 17 is inserted into the hole tip portion 16a of the insert hole 16, so that the positioning of the axis 17 or the valve 14 can be carried out.
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