Piston – ring – cylinder assembly of combustion engine has many friction pairs examples, also one of them which decide about fastness to wear, it means first sealing ring – cylinder, called further very simply ring – cylinder unit. During work of this unit, we can observe wear of piston, precisely – of coating which is deposited on ring to prolong service life. Objective of this work was to realize a test of set durability of railway engine EMD645 with power about 1300 kW. Within the framework of this test were investigated a prototyped piston’s rings with diamond embankment. Piston rings are made of diamond coating technology with a porous chromium coating, where in pores is deposited on said diamond powder with a grain size about 1 micron. The work will be carried out of an analysis of collaboration piston – rings – cylinder unit in internal combustion engine and an analysis of the use of hard materials in friction pairs, including powders. Will be performed research of material and description of diamond powder, which will be applied to the piston rings. After stability, testing in the locomotive engine EMD645 on the basis of the collected results will be developed conclusions of the wearing intensity on piston ring and relating them to the requirements for coatings. The work aims to show the possibilities and benefits of the application of new protective coatings on structural elements of the internal combustion engine in order to reduce their wearing, which is consistent with the observed trend of technology development.