Single rotor Wankel rotor engine for display. This is derived from the Grabcad model by Ravi Yadav (http://grabcad.com/library/wankel-engine-2) and converted into a 3d printable option. It will require some gluing and a piece of plexi-glass for the back. You can printout a back plate but i didn't like having the back covered. Enjoy
UPDATE
added a back plate just in case.

Do not scale down! gears are too fine to be printed any smaller. You will have to glue the outer gear to the rotor and the crank to the shaft [don't do this until you have a plexi-glass piece cut out for the back :) ] You will also have to sand a few of the parts so the spin freely. Enjoy and let me know what you think and if you made it.