There is some interesting engineering in a compound double acting engine[1], especially one like the Doble which runs on superheated steam. There's a large temp

There is some interesting engineering in a compound double acting engine[1], especially one like the Doble which runs on superheated steam. There's a large temperature gradient between the "hot side" and the "cold side" where the hot side is something like 1250°F+. IIRC they had to be careful about getting the correct cast iron alloys, and the bores had to be slightly tapered. Then there's the valve train, which is totally different from an IC engine but sizing and flow considerations are still really important for efficiency. Also, your crossheads and bottom end bearings are potentially an area of concern--while rotational speeds are really low by modern engine standards, there's a problem of figuring out how to remove water from the lube oil. So I'd wager there's still a whole bunch of "interesting" things happening in the Doble engine, and we'd probably have a pretty difficult time building one from scratch today given that reciprocating steam engines haven't been "a thing" in industrial living memory. [1] For one example of an interesting problem: for a given temperature of inlet steam and desired power output, in a double expansion double-acting compound engine, tell me what size the hot cylinder will be, what size the cold cylinder will be, and what the clearances, rings, etc will be to make it all work efficiently across the operating envelope.