Piston engine with a housing in which a shaft (19) is rotatably mounted in two pivot bearings of which at least one pivot bearing has an inner ring (26a) which is seated without radial clearance of motion on a supporting region (28) of a bearing section (19c) of said shaft (19). In order to prolong the working life of the at least one pivot bearing, the axial length of the supporting region (28) corresponds to a central region (a) of the bearing section (19c), a radial clearance of motion being disposed, at the two outer regions (b, c), between said outer regions (b, c) and the inner ring (26a).