Yeh, but what RPM's are you turning? Of my 5 they turn from 16,600 (worst) to 17,400 on a APC 9x6 and 15% PM fuel. I had one that turned 17,800 but it threw a rod and trashed the cylinder.
I did some messing with head clearance and found that the factory setting is fine. Any shims I tried either resulted in the same RPM or less RPM.
if everything is made correct then all you are doing is running in the bigend( and that has good clearance) and cleansing the engine.....
Sorry but, this is not true. You're not "cleansing" the engine. You're honing the various ABC metals at the expansion and temperature ranges where the engine will be expected to operate. Several engine manufacturer's disagree with you and running the engine too cool will ruin the piston/cylinder fit.
From K&B:
ABC engines are designed to run at operating temperatures, NOT COOLER temperatures.RUNNING THE ENGINE TOO RICH WILL RUIN THE FIT. If the operating temperature is not reached, the piston is prematurely worn from lack of clearance. You do not want to "break-in" an ABC engine at a very rich setting. Just a slightly rich setting for the first 30 to 45 minutes of running is adequate.
Although breaking in an engine in the air maybe ok, you can better control the process on a test stand for the first few tanks and then taking to the air.
SD