"Peter Dohm" wrote

It really is not my specialty, and I do not know in the case of aircraft
engines, or for current production automotive engines, but it was common
for
manufacturers not to "zero balance" a lot of the older automotive engines.
That means that the flywheel was heavier on one side because it acted as
either all, or more likely part, of one of the crankshaft balance weights.

That is now part of the function of the harmonic balancer, on today's auto
engines.
--
Jim in NC