Abstract: An air cooled rotor for a rotary internal combustion engine, such as a Wankel type engine, in which the housing has a two-lobed epitrochoidal bore which forms the cavity, the rotor having an outer profile of generally equilateral triangular shape with outwardly curved sides, such as convexly curved sides, and the rotor being mounted on an eccentric journal of a main shaft and being geared to rotate in a planetary manner within the cavity at one third of the speed of rotation of the main shaft, the rotor comprising a body and an insert secured together by one or more rigid fasteners which extend into a passage part of the insert from a passage part of the body which opens to the outer profile of the rotor, the or each fastener extending transverse to the axis of rotation of the rotor, at an angle of between 70.degree. and 90.degree. to the axis.