Method and apparatus for retaining a valve seat insert

A method of heat treating and retaining a ferrous valve seat insert in a countersunk valve bore of an engine component, said bore being defined by an outer cylindrical wall having a first diameter, said insert being defined by an inner frusto-conical valve seat surface, an outer cylindrical surface of diameter slightly greater than said bore's diameter, an annular blind recess extending from said outer surface towards said valve seat surface, the method comprising:

• i. pressing said insert into said bore to establish an initial compressive loading between said outer cylindrical wall of said engine component and said inner cylindrical surface of said bore said initial compressive loading established solely by pressing said insert into said bore at ambient temperature said annular recess being distorted when said insert is pressed into said bore;
• ii. inductively heating a predetermined first volume of said insert to a temperature at least equal to said austenitic temperature, said first volume extending from said frusto-conical seat surface towards said outer cylindrical wall a predetermined distance which is less than the distance from said frusto-conical surface to said outer cylindrical surface;
• iii. quenching said insert at a rate sufficient to form a martensitic structure in said first volume (a) so that the volumetric growth from said martensitic structure produces a deformation in the volume of said insert which has not heated above said austenitic temperatures to maintain an acceptable compressive loading, and (b) to further distort said annular recess whereby said compressive loading is maintained after quenching.

In combination, a cylinder head and an annular valve seat insert heat treated, in situ, from an initial condition to a heat treated condition by induction heating, said cylinder head having at least one combustion chamber, a cylindrical, countersunk valve bore in said head in communication with said combustion chamber, said countersunk valve bore defined by an annular base and an outer cylindrical wall extending therefrom;

• said insert within said bore having a bottom annular base surface in contact with said annular base, a smaller top annular surface, a generally cylindrical outer surface extending between said top and bottom annular surfaces in contact with said outer cylindrical wall and a frusto-conical seat surface extending from said top annular surface towards said bottom annular base surface the improvement comprising:
• said initial condition established solely by a press fit condition at ambient temperature;
• said insert having a first volume of a substantially martensitic grain structure defined by a cross-sectional configuration of said insert extending a predetermined first distance from said frusto-conical seat surface towards said outer cylindrical wall, a second volume of a substantially non-martensitic grain structure defined by a cross-sectional configuration extending a predetermined second distance from said cylindrical outer surface towards said frusto-conical valve seat surface;
• said first volume greater in said heat treated condition than in said initial condition to maintain said outer cylindrical surface tightly against said outer cylindrical wall whereby the press fit force between said insert and said countersunk valve bore in said initial condition is at least maintained in said heat treated condition.