Beautiful bit of engineering. Could it driven by compressed air? (I watched without sound) else it must be a diesel, as there are no spark plugs, like a model aircraft engine (which are small two-stroke diesels) . Glow plugs make diesels easier to start but aren't strictly necessary. It could have been run up by donkey/starter motor until the compression heated up the mass of the motor and it became self running.
Interesting that it is push rod, but I guess OHC might have been a bit difficult to build in miniature. At least it isn't two-stroke.
