Kyle's Plexiglass air engineThe machine runs pretty smooth although it won't run as fast as your wood model due to the Plexiglass being quite a bit heavier than plywood. Or perhaps my shop vac sucks :) .
I cut the valves using the band saw, my Rockwell Bladerunner table jigsaw and a lot of filing and sanding. I used the pictured hole cutter for the holes. You sure don't want to get near that while it's turning. I've used thinner Plexiglass, .093 to do some other projects and the thicker glass is easier to work with.
PS: oil helped the friction some. Still pleased.
Donald Zorn's air engine
Rodger's air engine
gas engine model