This is a parametric toy model of a piston engine, inspired by Neophyte's Air Powered Motor: http://www.thingiverse.com/thing:7792It is written in OpenSCAD, so you can change all the parameters and even animate it. It is kind of fun to animate it and change parameters on the fly.All the parts should be easy to print. Clearance between moving parts can be changed parametrically.Does anyone want to add some valves and make a real one that runs off compressed air?Download it and view it with OpenSCAD.The assembly is in toyEngine.scad.The files toyEngineParts.scad and toyEngineParts.stl have the parts aligned for printing.