The first thing to know about running in a ringed engine is that it's absolutely impossible to run them too rich. The richer they run the cooler all the parts are. This is a good thing for the first maybe 10 or 15 minutes. A ringed engine is similar to the old cast iron lapped pistons (or the new smaller Enyas) in that you have a cast iron seal against the liner. New cast iron is softer than the steel liner so it's used as a lap to polish the harder steel liner. If the cast iron (ring) stays cool it stays soft so when the liner has finished being lapped round and smooth you need to harden the ring. This is done by slowly leaning out the mixture from slobbering rich. The engine revs go up giving extra heat plus there's then extra friction on the surface of the ring. Short runs with a cool down heat cycles the ring and it gradually hardens until it's harder than the liner. This takes some time to do completely (several hours) but they're usually ready to fly after about an hour. You have to remember that you're working with totally different metallurgy to the usual ABC stuff.