A self pressurizing journal bearing assembly includes a tubular housing having a bore defining a plain cylindrical journal bearing, and a cylindrical rotary shaft disposed coaxially therein. The shaft includes a plain cylindrical journal spaced radially inwardly of the bearing to define a journal bearing gap. A screw pump is defined in part by a portion of the shaft, and is disposed inside the housing bore in flow communication with the journal bearing for continually circulating a lubricant thereto under pressure upon rotation of the shaft for accommodating lubricant end leakage from the journal bearing.