On Mar 18, 1:58 pm, nrp wrote:
"It is MUCH more important
to balance rotating parts than reciprocating."

I challenge that. Acceleration of a mass (or mass error) creates the
same dynamic force whether in a rotating motion or in moving in only a
translational motion. The only difference is that the force direction
is changing vs just reciprocating.

One gram may be overly accurate but it is something that is easily
achieved. I recall a Continental paper that said though that they
deliberately built up an engine with one pound (!) heavier piston & it
ran "satisfactorily".

Yeah, I'll bet......!

If one cylinder is oversized by .010" , the opposing cylinder
gets it, too. The heavier .010" oversize piston will throw everything
out of whack otherwise.
A one-pound heavier piston would run satisfactorily to someone
else, not to most of us. It would shake pretty good. Might get you
home, but that's about it.

Dan