As planned I removed the engine from the boiler, to discover why it would not work with compressed air yesterday.
I wish that I had checked this before going into print yesterday.
I discovered that the bronze cylindrical insert with the steam ports had never been fixed/Loctited into position. Clearly it had rotated with the first engine movements yesterday, causing all steam passages to be blocked. No wonder I couldn’t get the engine to do anything!
And worst was that I had mentally made a note to secure the insert, when I inserted it, a month or so ago.
So today I drilled and tapped a hole for a stainless steel grub screw to hold the insert into position. I decided not to Loctite it at this time, but will do so when I am sure that the timing is correct. I might need to alter the shape of the ports, and the insert would need to be removed to do that.
After reassembling the components I ran another test with compressed air.
Somewhat to my surprise, at 20psi the engine ran for a few revolutions, before settling down into a back and forth motion. It still needs to be timed, but hey, it moves. But by this time it was becoming hot in the workshop, so I left the timing for another day. Maybe tomorrow pm. Not Thursday because it will be HOT. 42ºc (107.6ºf)