| 摘要 |
PURPOSE:To improve the lubricating property and the corrosion resistance of a valve seat of an engine operated by alcohol for fuel, by using a ferro- sintered alloy impregnated with tin at least on the portion of the exposed surface side of a valve seat. CONSTITUTION:A valve seal 4 in a cylindrical shape is fitted in a step portion 5 at an opening end on the combustion chamber 1 side of an exhaust port 3 formed in a cylinder head 2. An exhaust valve 6 is seated on the valve seat 4 from the combustion chamber 1 side and a tapered surface 7 is formed on the portion of the exhaust valve 6 side. In this case, the valve seat 4 is made of a ferrosintered alloy with tin (Zn) impregnated in a multitude of small pores formed in the interior. Since tin lubricates a space between the exhaust valve 6 and the valve seat 4 by this method, abrasion between the two can be restrained. Moreover, alcohol used for fuel can not permeate into the valve seat 4 impregnated with tin, thus improving corrosion resistance.
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