1. Field of the Invention
The present device relates to a cylinder head for an internal combustion engine and, more particularly, to an improvement in the cylinder head having its body formed with a valve seat onto which an on-off valve is to be seated.
2. Description of the Prior Art
In the prior art method of forming a cylinder head body with a valve seat, an annular element made of a different material such as a sintered material is press-fitted in the cylinder head body or cast in the cylinder head body when the latter is cast.
In the prior art press-fitting method, however, the annular element which is made of a different material, has to be held by the cylinder head body. As a result, the holding portion becomes thick and deteriorates the coolability around the valve seat, which can cause knocking and a drop in the combustion efficiency.
In the prior art casting method, on the other hand, the adhesion between the annular member of the different material and the cylinder head body is poor and is degraded by the difference between the coefficients of thermal expansion. Thus, an interface is established between the body and annular member to cause problems similar to the problems discussed above.