How To Make a Steam Engine

Some Things to Note:
First off I should state that this steam engine is only a steam engine.  This  does not include  on how to build a boiler to produce steam.  Instead I run the steam engine on compressed air.  If you don't have a compressor a bicycle pump works well too, it's just a lot more work for you.  ; )

I should also note that even if you did build a boiler this engine probably wouldn't work well because many of it's major components are wood.  In the presence of steam the wood would swell and warp causing problems.  A simple solution to this problem would be to replace the wood parts with aluminum ones.

I am a very visual teacher so be sure to read the 'Image Notes' (hover your mouse over the yellow boxes on the images), it will likely make my instructions clearer. 

How it Works:
You could read my lengthy description below or you could check out the totally awesome animation by the guys over at  Science I should note that this animation is of a "double acting" engine, in that is has ports on both the bottom and the top of the cylinder where mine is a "single acting" engine with ports just on the top.  This just means that the engine relies more heavily on the momentum of the flywheel to keep it running but is a lot simpler to build.

This type of engine is called an Oscillating Steam Engine.  If you watch the video below you will see that the cylinder on this engine actually moves back and forth as the flywheel turns (it oscillates!), this action is what opens and closes the ports which let compressed air enter the engine and exhaust air leave. 

The cylinder has one port at it's top which is pressed up against the main body of the engine.  The main body on the other hand has two ports, one for the compressed air and one for exhaust.  As the cylinder tilts to the right it aligns with the compressed air port allowing air to flow into the cylinder and push down the piston.  This causes the crankshaft to turn, thus tilting the cylinder over to the left and allowing the air to exit the cylinder though the exhaust port as the piston comes back up.  Then the process repeats.