A method of cleaning of combustion engines, characterized in that it contains the following steps: a) a combustion engine is put in standstill condition; b) a piston of a cylinder of the combustion engine, which is intended for cleaning, is brought to the upper dead point position, in which position it is secured, and in case that the engine contains valves, these are closed; c) acid or alkaline chemical-technical liquid is led under the pressure within the range of from 0.1 to 2 MPa from the device for performing the method of cleaning of combustion engines that contains: at least one pneumatic-hydraulic or hydraulic circuit with at least one source of chemical-technical liquid with the working pressure of from 0.1 to 2 MPa, which is mechanically pressure-tight connected through a pressure tubing (12, 13, 26) and an adapter for mechanical pressure-tight connection to the combustion space of the combustion engine through a solid casing of the cylinder; through the pressure tubing (12, 13, 26) through the adapter to the internal space of the cylinder of the combustion engine, to the part above the piston in the position of the upper dead point; d) chemical-technical liquid from the step c) flows around the piston and piston rings through the spaces between the piston, piston rings and the internal wall of the cylinder, in the direction from the input of the chemical-technical liquid in the internal part of the cylinder above the piston in the position of the upper dead point, to the internal part of the cylinder under the piston in the position of the upper dead point, while possible contamination dissolves in the chemical-technical liquid; e) chemical-technical liquid from step d), which contains dissolved contamination, is led from the internal part of the cylinder under the piston in the position of the upper dead point through an engine oil drain opening or through channels in the casing of the cylinder out of the cylinder of the engine; while the group of steps c), d), and e) is at least once repeated so that when repeating these steps, a chemical-technical liquid of opposite pH is used than the chemical-technical liquid used on the previous group of steps c), d), and e). a) a combustion engine is put in standstill condition; b) a piston of a cylinder of the combustion engine, which is intended for cleaning, is brought to the upper dead point position, in which position it is secured, and in case that the engine contains valves, these are closed; c) acid or alkaline chemical-technical liquid is led under the pressure within the range of from 0.1 to 2 MPa from the device for performing the method of cleaning of combustion engines that contains: at least one pneumatic-hydraulic or hydraulic circuit with at least one source of chemical-technical liquid with the working pressure of from 0.1 to 2 MPa, which is mechanically pressure-tight connected through a pressure tubing (12, 13, 26) and an adapter for mechanical pressure-tight connection to the combustion space of the combustion engine through a solid casing of the cylinder; through the pressure tubing (12, 13, 26) through the adapter to the internal space of the cylinder of the combustion engine, to the part above the piston in the position of the upper dead point; d) chemical-technical liquid from the step c) flows around the piston and piston rings through the spaces between the piston, piston rings and the internal wall of the cylinder, in the direction from the input of the chemical-technical liquid in the internal part of the cylinder above the piston in the position of the upper dead point, to the internal part of the cylinder under the piston in the position of the upper dead point, while possible contamination dissolves in the chemical-technical liquid; e) chemical-technical liquid from step d), which contains dissolved contamination, is led from the internal part of the cylinder under the piston in the position of the upper dead point through an engine oil drain opening or through channels in the casing of the cylinder out of the cylinder of the engine;