Abstract: A machine for machining the inner walls of the cylinder of a Wankel engine in which a support is provided for the cylinder to be machined which rotates the cylinder about a first axis in one direction with the first axis moving bodily about a second axis in the opposite direction. Cutting tools are provided which engage the inside of the wall of a cylinder mounted on the support and effect cutting thereof during movement of the cylinder. The tools are mounted on support elements which are pivotal about lines substantially coinciding with the lines of engagement of the respective tools with the cylinder wall of the cylinder and are pivoted during movement of the cylinder to maintain substantially the same cutting conditions between each tool and the cylinder.