| 摘要 |
PROBLEM TO BE SOLVED: To prevent subsidiary exhaust port or exhaust port from connection with scavenging port despite that the area of openings thereof are enlarged, by plugging up the pin hole, opened to the outer surface side of the piston, with filling material, and by forming the radius of curvature of the outer surface of the filling material in the direction of the circumference same as that of the outer surface of the piston. SOLUTION: Filling material 10 is plugged in the side of open end 41a of pin hole 41, which penetrates the piston 4. A protrusion 11 is formed on the outer surface of filling material 10, and outer surface 10a of which is formed so as to have same radius of curvature of outer surface 4a of piston 4 in the direction of circumference. In this way, the filling material 10 plugs up the open space the open space A formed in the side of open end 41a of the pin hole 41. By the reason that scavenging port and subsidiary exhaust port do not connect with each other, exhaust gas does not flow backwards from subsidiary exhaust port to scavenging port, and the output of the engine is prevented from lowering. Moreover, output power is improved by widening of the size of exhaust port opening.
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