Hydraulic piston engine driven by a lubricant-free, water-based fluid

A hydraulic piston engine for operation with a lubricant-free, water-based pressure fluid, having a rotatable shaft which is coupled to work pistons and which is journalled in a housing in at least one radial journal bearing, in which a first sliding surface of metal faces a second sliding surface of plastic material, including, in the journal bearing in a load area, which is continuously loaded during operation by the influence of the work pistons with a radial force (F.sub.rl)+F.sub.rp), at least one recess shaped in one of the sliding surfaces, which recess is supplied with pressure fluid during operation for at least partial absorption of the radial force, and the recess having an areal center of gravity being angularly displaced an angular displacement (.alpha.) in a direction against the direction of rotation of the shaft in relation to a certain position determined by geometry of the engine, which position indicates the areal center of gravity for an area where the radial load (F.sub.S) from the work pistons would exist on the second sliding surface, if the journal bearing was without friction and without said recess.