4, b, it is intended to test the hypothesis of constant friction torque accepted in the case of dry friction pairs for the symmetrical rotor; if the assumption is confirmed, it allows for finding the coefficient of sliding friction from the rotation pair, parameter required for the simulation of the asymmetric rotor motion.

[mathematical expression not reproducible] (26) resulting in an equation from which the coefficient of sliding friction may be found.

When the inner surface of roller and external surface of axle worn down [1], then wood shavings fall between them, and at 100 % contamination by wood chips ([xi] = 1), we have [f.sub.r] = 0.36, which corresponds to the similar value of

coefficient of sliding friction between two metallic surfaces in dry operational conditions--[f.sub.sd] = 0.35 ...

For improving antifriction molecular treatment of inner surface of cylinder at spark ignition engine, the lubricated oils are additive with addition of solid lubricates under micropowder form as: polyethylene terephthalate (PETE), colloidal graphite, bisulfate of molybdenum (Mo[S.sub.2]), which compacted heterogeneous antifriction film, reducing

coefficient of sliding friction in piston-cylinder couple (fig.7) [Ungur,2007].