The article is devoted to the questions of technical operation of the internal combustion engines. The engines of this type are widely applied in transport, agriculture, power engineering, etc. The article overviews some problems of the technical diagnostics of the piston rings. The resonance method for the examination of the current technical condition of the piston rings is described in the paper. The undamped oscillations are excited in the ring at the frequency of its own mechanical resonance and at multiple harmonics. The amplitude of the ring oscillations is measured in the gap by means of sensors according to two coordinates simultaneously. The piston ring has a gap and is fixed at one point opposite to the gap. The two half-branches of the piston ring form a kind of fork. Oscillations in the ring are excited by an electromagnet. By means of an amplifier, the electromagnet is connected to an electromagnetic sensor placed close to the gap of the ring. Thus, a positive electromechanical feedback is formed. This system forms undamped oscillations with frequency and amplitude depended on the mechanical properties of the ring material and its geometry. Micro-cracks, the areas with stresses, hardening defects, local overheating, loss of elasticity and other defects cause the deviations of frequency, phase and amplitude from the standard. Theoretically, the cross-section of the piston ring can be considered rectangular. But really it has a complicated form with grooves, holes, and its resonance frequency is difficult to calculate. Therefore, the reference values should be assumed as the average results of the measurements of serviceable piston rings. The technical condition of the piston ring of the ship’s diesel with 630 mm diameter in resonance condition is investigated experimentally. The results are obtained and analysed. Such method of diagnostic can be applied at the initial examination of the rings as well as at determination of the reasons of defects during the operation process. One of the special features of the proposed method is the registration of the frequency response of the piston ring’s oscillations simultaneously in two planes – radial (the plane of the ring) and in the direction of axis. It allows to discover the defects (microcracks, thermal inhomogeneity, etc.) of the ring independently on their orientation along the assumed axes. At a scheduled examination taking part during the operation the pistons and the rings are removed with further cleaning of the grooves and rings. Under the conditions of the vessel the degree of deterioration is checked by means of measurements of the geometry and gap of the ring. The rings meeting these requirements are applied repeatedly. Thus on the vessel the control of the located mechanical pressures, presence of microcracks and other defects is impossible. The method, proposed by the authors in this paper, is relatively simple and enough informative.