It had a sliding double-action (push-pull) piston and a push-pull valve operated by a linkage attached to the flywheel. I didn't make a boiler - just ran it on

It had a sliding double-action (push-pull) piston and a push-pull valve operated by a linkage attached to the flywheel. I didn't make a boiler - just ran it on compressed air. It vibrated ferociously, though, as I had paid no attention to balancing it.