This is my first contribution of my own design to Thingiverse! I designed it in Rhino and printed it on my TOM. I left a lot of space in the piston cavity and it could probably be tweaked but it works great! Makes a good demo for children or if your bored give it a whirl! Big thanks to my friends at Makerbot support, Matt made this possible!

I printed it in two sizes, one at 100% and the other at 75%, that is the one pictured; It turned out way better than the larger one. I'd like to see one super small if you can pull it off! Pretty straight forward assembly .Print the tray, The dog bone has a smaller end for the piston and the bigger one goes on the flywheel shaft. It prints well but requires a little bit of alteration to the holes to get them to fit just right. I was able to assemble it glue free!