Abstract: An epitrochoidal Stirling type engine operating on a carnot cycle. The engine has a hot end and a cool end. Each end has a three-lobed rotary piston or rotor eccentrically mounted. Each rotor is in a four-lobed housing. Between the rotors, coaxially mounted is a cam similarly eccentrically mounted which is captured between peripherally mounted rollers so as to guide it in an orbit with precision. The cam is secured to the rotors so that they similarly orbit in precision in their housings to eliminate peripheral seals. Lobes of the two rotor housings are connected in pairs, the lobes of each pair being angularly spaced 90.degree.. There are connections for fluid flow between pairs of lobes with regenerators in the connections. The thermodynamic cycle corresponds to that of the Stirling engine. Heat is applied to one end of the engine and heat is discharged at the other end. The engine produces a power output.