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It depends on the application. Large engines are usually low rpm engines with huge connecting rod and main bearings. The Cooper Bessemer's my brother used to work on ran around 150 rpm but they had a 12 foot diameter flywheel. You could crawl through the cylinders.
Here is a link to a type 26 running.
https://www.youtube.com/watch?v=b78BELn8U2M