ORIGINAL: downunder
Dar,
It's good to see you've changed your ideas away from your original doomsday prophecies of "Run it rich for even one tank and you might as well throw away your engine" as I well recall you telling one newcomer.
Maybe it's worth repeating that my experiment wasn't to say an ABC should (or could) be run in slobbering rich but only to find out what damage might be caused instead of just going BAAA BAAAAA and following the sheep.
Brian,
I did write in the tapered-bore break-in thread that the wear on the piston crown, will be greater if break-in is done four-cycling rich.
I also wrote that ABN engines will be more susceptible to peeling, in these conditions.
This peeling will not happen during the break-in. It is more likely to happen, however, when the engine is peaked-out (or run too lean), long after the break-in is completed.
The interference fit and contact of the piston in the sleeve during a cold, 'wet' break-in, will potentially weaken the bond of the nickel coating to the brass bore.
And...
Load will be imposed upon the nickel/chromium plating, even if no metal-to-metal contact occurs...
The oil-film relays the load to the surfaces, even when it remains intact, as fatigue wear in babbit, Clevite 77 and other bearing materials (in full-size auto engines) would indicate.
So even if wear cannot actually be seen, or measured, it could just be there nevertheless.
I am also saying that even if a four-cycling, rich break-in will cause no immediate visible damage, it is not the best, or even the correct way of doing it.
From your own testimony sometime in the past, you do the break-in of your own tapered-bore engines (and those you are entrusted with their break-in), in a method similar to what is described in the tapered-bore break-in thread.
I am not talking about your experimenting, to prove nothing will happen (...); just about your general practice.