Had a discussion at field about correct engine breakin procedure, encountered considerable range of opinion. I recall reading that for ABC, need to get engine up to operating temperature and that running rich and slow would just wear out the engine. Ringed called for temperature cycling, that is, running 1 minute at operating temperature, then stop and let cool ( or alternately richen up to cool it off ). Curious what "experts" say in this regard, we have many at our field with wide range of opinions. My experience hasn't been particularly broad as am partial to the plain bearing ABC(N) like OS FP series, usually just run them on rich side with castor blend ("break in" flying) and don't worry too much.

Well if you want opinions, you won't be short of any here. Lets say you get to opinions here, go with the majority. You find several answers from pluto somewhere but a few will be similar which is what you go with and what makes sense.
*You will find that here and your airfield people make things alot harder on themselves than they have too. You can also go by the manuals.
* As far as breaking in an ABC. I just take it to the field, run it up and tune it in. On the average it takes a tank or two to get it dialed in. Then i run it a tad rich and thats it. Go fly it. I break in a ringed almost the same but i fly it noticably rich for a few tanks.
Your going to find a thousand ways of doing it but whatever.
* In the winter time here it get cold but no snow. I run it up, tune it in. Then refuel real quick and tune it in again because it is cold, then when the engine warms up, things tend to expand like O-rings and such.

There was an excellent article entitled "Break-in: the secret to longevity and reliability" in the November 2001 issue of Model Airplane News. Its too long to include here; maybe you can get a reprint.

Most people will say just read the manual and do what it says...but have you ever tried deciphering something like the Rossi instructions?? Both Rossi and Jett (who you gotta admit make some pretty good engines) say that you have to run them in for between 30 and 40 minutes at what they call a rich setting. The problem is that this "rich" setting isn't particularly well defined (Rossi for instance says the exhaust should be "greasy" ) but by reading between the lines it seems that what they intend is for it to be running in a 2 stroke but that even one or two clicks richer will make it drop back to a 4 stroke. In other words, run it at a point just beyond the transition from a 4 stroke into a 2 stroke mode.

The official OS engine web site (not the American importer's but the factory) actually says that the first run should be one minute in a rich, slow 4 cycle then the remainder of the first tank should be cycled every 10 seconds between a 2 stroke and back to the rich 4 stroke. Then 3 or 4 tanks with the needle set so it's just broken into a 2 stroke.

With all of this I've tried to avoid just giving my own opinion. But one thing that Jett states is that the majority of the running in is not for the ABC piston/liner but for the con rod.