Here we have an engine running at 0 rpm.

“But”, pedants will say “it’s not running at 0 revs. It’s doing about 90% of a rev one way and then another 90% the other so overall it’s doing something like 60 rpm”.

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Away with you, pedants. After running for a minute it still won’t have achieved a complete revolution.

Zero rpm.

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What puzzles me is how an engine that fires so far ahead of TDC ever gets to run in one direction.