Abstract: An improved rotary mechanism such as a rotary engine. The mechanism includes a main shaft with a rotor supporting portion thereon. A rotor is journalled on the supporting portion and has a plurality of apices. Each apex is provided with a seal retaining groove and a seal is disposed therein. A plurality of hydraulic passages are provided in the rotor, one for each apex seal, and open from the rotor to the rotor supporting portion of the main shaft. The rotor is provided with suitable devices for transmitting hydraulic pressure applied in each of the passages to the corresponding apex seal to bias the apex seal out of the groove into good sealing engagement with the operating chamber walls. A hydraulic fluid conduit is located in the main shaft and has a port terminating in the rotor supporting portion. The port is disposed to be periodically, serially aligned with the passages in the rotor for timed biasing of the apex seals as desired.