The scope of the study is limited to the period of closing valve, but phenomena existing in the antecedent phase influence conditions in the contact between seats. Friction type in such contact varies from mixed to boundary or even dry one, depending on the amount of oil and wear debris wherein. The operational conditions for inlet and outlet valve are different because of temperature in contact and deposition of carbon deposits. The complexity the phenomena in contact zone, including valve rotation makes difficult the modeling of friction. The valve rotation is considered only in macro scale and the other displacements of seats in micro and macro scale. The initial shape of seats resulted from grinding and lapping process varies during impacting and abrasion wear. The aim of the studies is to obtain courses of friction force between seats, as a function of engine speed and load, duration of wear process, for some material association of valve and its insert in conditions of dry and boundary friction. The elaborated models of friction between the seats use fractal and statistical models of roughness the mating surfaces. It is used the geometry of the valve and its seat insert from the selected engine. The dynamic of valve motion and heat transfer between valve head and its seat insert has been modeled using the FEM. The values of dry friction coefficient have been estimated during earlier tests of samples made of the valve material and counterparts made of material the seat insert.