RE: How important is the break in procedure?
PK,
I'll begin from the end. No, I have not extensively modified any model engine.
I also never competed, or raced with model glow engines.
I only broke many of them in and overhauled and rebuilt many more, using stock or replacement parts.
That is my experience, from which I learned a great deal (many don't learn).
I did overhaul 38 real car engines and hot-rodded several.
I am no engine expert, but my understanding of their dynamics is probably a lot better than the next Joe.
If you read [link=http://www.rcuniverse.com/forum/m_1850473/tm.htm]the tapered-bore break-in thread[/link], you'd see it compiles techniques written by; among others, the persons you mentioned in your last post.
As to heat-cycling; do you actually think alternating the temperature of a high-silicon aluminium piston, from 150°F to 250°F and back, constitutes 'heat-cycling'?
I can tell you it has no effect whatsoever on the metal. You can search any text book, or professional web site that you like; and you still won't be able to refute my words.
These words 'heat cycling', when used to 'typefy' a break-in procedure for an AB(X) engine, are nonesensical; less than 'buzz-words'.
When meehanite-steel engines are discussed, cycling the temperature of the piston, between room-temperature and ~200-275°F, does have an effect of stabilizing the growth of the piston.
This is also true to a degree, as far as the cast-iron ring of a ringed engine is concerned.