| 摘要 |
PURPOSE:To prevent carbon from adhesion to an exhaust port, by a method wherein an approximately spherical recessed part is formed in one spot or spots in the inner wall surface, being in the vicinity of the opening part of the cylinder, of the exhaust port. CONSTITUTION:An exhaust port 3, and a scavenging port 4 are formed in the inner peripheral surface of a cylinder 2 of an engine, and the two ports 3 and 4 are designed to be opened and closed by means of a vertically moving piston. The exhaust port 3 is formed approximately in an oblong in cross section, but in this case, recessed parts 7 and 7 are formed in an inner wall surface 5 of the exhaust port 3 in a position, which is situated in the vicinity of an opening part 6, being open to the cylinder 2, of the exhaust port 3, and in a spot, where an oil content is apt to adhere, i.e., two corner parts on both sides of the upper part of an oblong shape in cross section. The recessed part 7 is relatively small and is so formed that its inner surface forms a part of a spherical surface. This constitution prevents carbon from adhesion and retention to the exhaust port 3.
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