Piston unit for combustion engine

Piston assembly (1) for an internal combustion engine comprising an upper section (2) abutting onto the combustion chamber of the cylinder, a piston skirt (3) in connection with the upper section, and a sealing arrangement for sealing the joint between the upper section and the skirt. In the piston assembly the sealing arrangement (1.2, 1.3) between the upper section and the skirt is provided by utilizing the difference between the mounting and working temperatures of the upper section (2) and the piston skirt (3). Preferably, the sealing arrangement between the upper section and the skirt is arranged to operate under working pressure and the sealing arrangement comprises several operationally in succession provided counter surfaces, which are arranged with respect to each other so that their mutual distance is reduced at the working temperature of the surfaces, and that a pressure balancing chamber is formed between two successive, tightly arranged counter surface pairs (2a - 3b).