An adjusting mechanism for the annular inlet of a radial inflow turbine employing a rotatably mounted adjusting ring as one side of the annular inlet with cams and biased slots controlling primary vanes located within the inlet. A clamping ring which is capable of moving axially is located inwardly of the adjusting ring. A bearing piston ring is mounted to the clamping ring and supports the adjusting ring. The bearing ring also provides some sealing capabilities. A sealing ring between the clamping ring and the housing accommodates some small axial movement of the clamping ring and seals against substantial pressure differential between the inlet and outlet of the nozzle itself. Pins extend across the annular inlet to pivotally mount the primary vanes.