Cylindrical Interference Fits for a Secure Hold
Cylindrical interference fits are used for achieving friction-type connections between components such as cylinder head and valve seat. Especially in such a case where different metals with different coefficients of thermal expansion are joined together special care has to be taken for a tight connection even at working temperature. Therefore at room temperature the oversize of the seat ring is so big that it is impossible to force it in without damaging the bore.
A suitable procedure is a combination of heat shrinking and cold expansion:
The cylinder head is heated while the seat rings are cooled. Then the ring is dropped carefully into the bore. With the following temperature equalization the bore is shrinking while the ring is expanding. Thus a highly stressable interference of the join is achieved.