Abstract. The article is devoted to the questions of technical operation of the internal combustion engines. Some questions of the technical diagnostics of the engine piston rings are considered. The authors propose a resonance method for the examination of the piston rings. The idea of the method is to cause oscillations in the ring at the frequency of its own mechanical resonance and at the multiple harmonics. The amplitude of the ring oscillations is measured in the gap by means of sensors according to two coordinates simultaneously. The frequency, phase and amplitude of the oscillations depend on the mechanical properties of the ring's material and its geometry. Micro-cracks, the areas with stresses, hardening defects, local overheating, loss of elasticity and other defects cause deviations of the frequency, phase and amplitude from the standard. One of the special features of the proposed method is registration of the frequency response of the piston ring oscillations simultaneously in two planes -radial (the plane of the ring) and in the direction of the axis. It allows to discover the defects (microcracks, thermal inhomogeneity, etc.) of the ring independently on their orientation along the assumed axes. This is a kind of non-destructive methods.Keywords: diagnostics, oscillations, frequency, amplitude, resonance. IntroductionThe piston rings are one of the important parts of the cylinder-piston group of internal combustion engines (ICE). A piston ring operates under very severe conditions -high temperatures, in the environment of aggressive chemical gases, with significant alternating mechanical stresses. The ring experiences continuous flexural-torsional vibrations in the grooves of the piston. The purpose of the piston ring is to segregate the combustion chamber and the crankcase space. The oil is supplied to the combustion chamber under the condition of increased gaps, the gases leak from the combustion chamber into the crankcase. This results in a significant deterioration of the technical and economic parameters of the engine and reduction of its service life.The paper suggests a method of present technical condition of the piston ring determination and analysing its frequency response plot (FRP) of its forced and self oscillations. The measurements are realized at the frequencies close to those of its own mechanical resonance and its harmonics. Thus, the piston ring plays a kind of tuning fork. Then the obtained FRP are compared with the reference plots.