| 摘要 |
PROBLEM TO BE SOLVED: To fit a cylinder head therein with an intake or exhaust port which is asymmetric relative to the center line of a fluid passage in the port by machining the inner surface of a hole corresponding to the port and a valve sheet stock after the valve seat stock is diffusion-bonded to the combustion chamber side end part of the hole corresponding to the port, and the valve seat upon formation thereof, with a bonding depth which is circumferentially uniform. SOLUTION: The inner surface of a port corresponding hole 25 formed in a cylinder head material 26 before a valve seat material 27 is diffusion-bonded thereto, is formed, in a part thereof to which the valve seat material 27 is diffusion-bonded, in a curved shape that has a basic shape which is defined by superposing loci obtained by rotating the inner surface of the intake port 15 having a completed shape around the center line C of a passage, and that is convex toward the center line C of the passage.
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