Abstract: In accordance with one aspect of the present invention, an improvement in the combustion chamber of an internal combustion engine (10) is provided. A spherically shaped rotating element (22) is mounted in the engine head (20) for rotation about a first axis (24). The rotating element has a notch which aligns between the combustion chamber and inlet and exhaust passages as the rotating element rotates. A seal assembly (42) seals against the spherical rotating element. The annular seal (54) in contact with the rotating element rotates about an axis and is self-centering in its sealing action to reduce wear and increase sealing effectiveness. The annular seal is mounted and urged into sealing engagement with the rotating element with nested annular seal retainers (56) which also rotate.