There is a fellow that does some Demos for Sherline Co.Jerry Kieffer, He built a working Harley Davidson engine powered by some type of liquid fuel, my guess would be model airplane fuel, he even made the Spark/ Glow plugs, the motor was just over 1.5 inches from the bottom of the crank case to the top of the heads, and it ran.
I love watching guys like him, he has more work than he can handle, besides the advertising Sherline toys, and was getting 2 bills an hour, it's amazing what some of these Miniature machinists get, and the demand in large metropolitan areas, PLUS there is a bunch of money for prizes at shows like N.A.M.E.S. The V12 engine is pretty darned cool. I can't imagine how long the different setups took. or how many hours it took to machine it.