Engine valves

Abstract

An engine valve according to the present teaching has a hot-forged head portion having an oxidized surface layer at a radially outer peripheral surface. The oxidized surface layer is formed during hot-forging of the head portion.

1 . An engine valve comprising:
 a shaft portion and a head portion each made of heat resistant alloy;   wherein the head portion is disposed at one end of the shaft portion in continuity therewith and hot-forged without forming any burr at a radially outer peripheral surface of the head portion;   wherein the radially outer peripheral surface of the head portion is not machined so that the radially outer peripheral surface of the head portion has an oxidized surface layer formed by oxidization of the heat-resistant alloy.   
     
     
         2 . The engine valve as in  claim 1 , wherein the radially outer peripheral surface of the head portion has a curved configuration. 
     
     
         3 . The engine valve as in  claim 1 , wherein the heat-resistant alloy is heat-resistant steel. 
     
     
         4 . The engine valve as in  claim 1 , wherein the heat-resistant alloy is titanium alloy. 
     
     
         5 . The engine valve as in  claim 1 , wherein a surface of the engine valve includes a flat head surface, a valve face formed in continuity with the head surface via the radially outer peripheral surface, and a neck surface having a diameter decreasing toward the shaft portion. 
     
     
         6 . A method of manufacturing an engine valve, comprising:
 preparing a rod made of heat resistant alloy;   forming the rod into an intermediate product having a shaft portion and a head portion primary body; and   hot-forging the head portion primary body into a head portion, so that an oxidized surface layer is formed on a surface of the head portion without producing any burr at a radially outer peripheral surface of the head portion.   
     
     
         7 . The method as in  claim 6 , wherein the step of forming the rod into the intermediate product comprises forging a portion of the rod into the head portion primary body.