Similarly, the shafts on jennies and the like are typically drop-forged in a oner, whereas the big ones are forged in individual bits then the pins, webs, throws and everything else are shrunk-fit together. Then you just need a really big crane.
Usually, the engine is assembled in the factory, tested, then taken to pieces and shipped to the other side of the world. There it's put back together on the ship as it's being laid down and then never works as well as it did in the factory tests. And if you ever need to take an engine or jenny out of your ship, you have to cut a sodding great hole in the side of the hull

Very, very big turbos too ^_^