This is a short 3-minute video by “rbandes1” that shows and explains the operation of the “Jingle Bell Steam Engine” he made. It was built from free plans provided by Professor Nial McCabe, who teaches Engineering Technology at the County College of Morris in Randolph, NJ. Professor McCabe has one on display with a main bearing that has become loose from heavy use. As a result the flywheel lightly touches the frame when it turns, creating a “Jingle Bell” sound. That’s how it got its name.
Paul Jorgenson also built one of these engines. His version is a little bit simpler and he has a very nice set of plans (PDF) for it. Paul also has lots of photos showing its construction over on the Home Model Engine Machinist forum.