ORIGINAL: DarZeelon
The objective of break-in, in an ABC/ABN/AAC/ABL model engine, is to mutually mate the piston to the sleeve (and to a degree, the con-rod the the crank-pin and to the wrist-pin).
It is not intended to heat-treat any of the parts, or to aneal them (make them mallable, ductile).
This whole discussion has 'flown off the handle' several pages ago.
We're discussing metallurgy; instead of debating the OP's original question.
Let's get this thread back on-track.
As was explained to me, by a respectable engine manufacturer, the ABC fit is at its best when it leaves the factory. The only "break-in" required is for parts other than the piston/liner combo. But I know that no one will agree with what I'm repeating. How do those stupid engine manufacturers continue to stay in business year after year? (smile)
Ed Cregger