Having recently finished my first steam engine (One of Elmers simple wobblers), and being a veteran insomniac, I was laying in bed the other night wondering just how small the worlds smallest piston engine is, and how large the largest one. I never messed around with model airoplanes, so really the smallest piston engine I have ever seen is the 3/8" diameter engine that I just built. I have seen pictures of really large engines in trans Atlantic ships, and I am curious ---would the largest piston engine be something current, or would it have been built at the time of the industrial revolution. I don't care if it was steam, gasoline, or diesel---long as it was a piston engine.