The paper contains new results of the investigations announced by the authors in 2017, 2019 in the materials of „The 16th, 18thInternational Scientific Conference Engineering for Rural Development”. The work is devoted to determination of the current condition of one of the most loaded elements of the cylinder-piston group of the vessel diesel engines – the piston ring. A new experimental board with a strengthened construction has been built. The piston ring with a gap is placed in a vertical position, it is fixed at a single point symmetrically to the gap. Its both half-segments form a fork. The board has an increased number of magnetoelectric sensors for a simultaneous registration of oscillations of the both segments along the radial and axial surfaces – X and Y. The oscillations of the ring are investigated in a regime of free and forced oscillations. In the regime of free oscillations, the ring experiences a single impact of a ball with a particular mass, length of its pendant on the angle of the shift. In the regime of forced oscillations, the ring is excited with the undamped oscillations on the frequency of own mechanical resonance and on the even harmonics. The frequency of the oscillations, phase and amplitude depend on the mechanical properties of the ring material and its geometry. The basic frequency of the forced oscillations for the first harmonic is determined experimentally and differs from the theoretical frequency obtained with mathematical modelling for 12-15 %. Mechanical oscillations of the ring have larger difference from the theoretical on the higher harmonics with frequency 2f1, 3f1. At the first stage of the diagnostics the parameters of the left and right segments are compared with each other. A ring without defects has similar parameters of the segments. The second stage of the diagnostics is the comparison of the obtained results with reference values that are average results of measurements of some serviceable rings without defects.