| 摘要 |
PURPOSE:To prevent damage of a valve stem by forming a corner portion of the inner peripheral surface of a valve spring seat by a curved surface portion with a small radius of curvature and a connecting portion with a large radius of curvature, hardening the surface thereof and then grinding same. CONSTITUTION:A corner portion 9b of the inner peripheral surface of a valve spring seat 9 is formed by a curved surface portion 13 with a small radius of curvature and a connecting portion 14 with a large radius of curvature. Secondly, the valve spring seat 9 is subjected to surface hardening, and the subjected to grinding to the final inner peripheral surface 9a with a portion of the connecting portion 14. Thus the corner portion and the inner peripheral surface portion can be smoothly connected to each other so as to prevent damage of a valve stem.
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