Thank you gentlemen. Yes, I knew it was going to work well when I could get it to (just barely) maintain rpms using just lung pressure. Helped to have my 15 yr old trombone player providing said air pressure
I had some goofs in the build, but was able to figure out how to correct/compensate for them.
The "next" project was to make a steel body for a filter-drier for 3000 psi air for my high-pressure air rifle; then (after breaking a #6 tap during that project, using a crappy hardware store t-handle tap wrench) I took some time to make a knockoff version of the Starret No. 174 tap handle (YouTube's mrpete22, Lyle Petersen, had a series of videos where he made one, and I sorta copied it), maybe I should post a picture or two in the tools section?
But I've also redrawn a set of plans for a slightly upscaled version of Elmer;s Standby, using larger diameters for flywheel and crankshaft, so that's likely next for engines. I want to work through a few more of Elmer's plans...but may wait until I get a mini-mill, as using the company's drill-mill has its drawbacks.
And all the build logs and discussion on here almost makes me want to try an IC engine!