Just came across this one, showing a MASSIVE marine powerplant under construction: http://www.bath.ac.uk/~ccsshb/12cyl/ Now THAT'S some "heavy metal"! I particularly liked the ladder rungs welded inside the crankcase, so a mechanic can crawl down into the oil sump for inspection! It's a wonder that anything like this can actually be built, considering the degree of precision needed on components that large. Imagine the lathe that was needed to turn the journals on that crankshaft, for example....
Yeah, that's a big one, but my father was in the Merchant Marines during WWII, in the engine room of lots of ships. It seems to me they had steam engines that were that big. Several stories tall I think. I'd have to ask him. Not as many cylinders though probably. Lots of them had wooden bearings on the rods. He also worked around the world on industrial turbines and the plant he worked for had lathes, mills, etc that would handle that stuff, huge things. I'm sure that crank is assembled in parts.