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An early twentieth century Heinrici hot air engine, one of the smaller engines they produced for a wide variety of applications before small, fractional horsepower electric motors took over in the 1920s.

Believed to be of 1912 vintage, the engine is in good condition and runs beautifully - light the burners, leave it a minute or two, turn the flywheels once and it's off! Quiet in operation, there's some video of it running this afternoon here.

A beautifully made machine, it's well-equipped with oilers to allow prolonged, unattended running. The displacer drive is elegant, the displacer rod concentric with the piston and passing through it, driven by a crank and lever from one flywheel.

The engine, on its cast iron stand, is mounted on a wooden base along with a water tank for cooling - circulation is by simple thermosyphon.

The twin jet burner runs well on butane - a cooler flame than propane which gives the hot cap an easier life.

Complete with two spiral bound volumes of "Vintage Hot Air Engines" by Gerd Maier, a pair of telephone directory-sized books bringing a whole new meaning to the word "definitive".