It started out as this pile of leftover parts from past Hot Wheels builds.
All of that got turned into these bits.
Gotta have some semi-unique tools to do all that though. The jewelers saw and pin vice / jewelers drill are lotsa fun to play with.
Getting the rotating assembly put together.
Piston, cylinder, and associated bits.
This type of engine is commonly called a "Wobbler" or an Oscillating Steam Engine, because the entire cylinder wobbles back and forth. As it does, one of these holes lines up with the hole in the cylinder, letting pressure in to push the piston down. On the way back up, the other hole lines up and lets the pressure out.
And of course, some videos of it running. First one shows me powering it with my lungs and then a longer run with the air compressor. Second vid was the second time I had ever gotten it to run, using the air compressor on that one.
This was a lot of fun to make. It was even more fun to watch the band teacher, who you would think has lung capacity to spare, turn red, then purple, then white trying to get it to go!
Also wrote an instructable on this one and entered it into a couple of contests over there. Check it out here: http://www.instructables.com/id/Penny-Engine-micro-air-powered-engine/
