Hi Downunder,

That is a very interesting way of looking at it. I know that the piston head does not expand nearly as much as compared to the sleeve. I never really thought that the piston head might not expand either due to the cooling. If this is true, then there should be no worry of the piston head wearing the sleeve down prematurely. To me, break-in is metal rubbing metal, not metal hammering metal. If by peoples comments here that they have suffered no ill effects by following the manual's method, then both methods work well for different reasons and we all benefit with long lasting powerful engines. I agree with Brett65 about the exhaust appearance - completely normal in the beginning - especially with ringed engines. Thanks for the engaging conversation.

Happy flying!