I found a broken garden tool handle that fits nicely inside some PVC pipe I have, so naturally it had to become an engine. I came up with this simple design. The wood handle will be the piston and valve, the latter having offset ports in it for intake and exhaust and being perpendicular to the cylinder, pivoting back and forth via a connecting rod. Here's a couple quick sketches and photos.
Photo A: the piston is all that's currently anywhere close to being done.
Photo B: I'll make the connecting rods from this old hacksaw blade.
Photo C: The fit of the piston inside the PVC pipe.
The crankshaft will be bent out of some thick wire.
