This engine has some metal (brass, aluminum) parts, couple of metal screws and some rubber O-rings, but that is unavoidable due to the nature of the technology and ABS material limitations.
It takes some 50 deg F (or 28 deg C) of heat differential to move at stable speed at about 300 rpm without additional weight or load.
All the 3d files and plans to make this Stirling engine can be found at:
Here is video demonstration of the engine in action:
|Doug's DIY 3d printed Stirling engine from the project homepage|