Recently my friend rebuilded my '84 Yamaha TT 600, bottom end etc. New main bearings, crank case bearings, some new gears, crank pin, conrod, Wiseco 11.5 to 1 piston off ebay (actually got it cheaper than stock piston) Obviosly new gasket set. I have done 180km with the bike after rebuild sofar, and the Clymer manual reccommends 1000km after that I can use it pass half throttle. I am doing exactly what the manual describe. But if I accelerate a bit quick and getting near half throttle it makes a noise like the compression want to push out at the top gasket. Could it be the new piston still "settling in" Cant see oil residue anywhere near the top gasket. My friend used the info from the manual to torque the head accordingly, even a little bit more cuz I have now a 11.5 to 1 piston instead of a standard 8.5 to 1 piston. Is this normal, will this go away eventally after I have done the 1000km's? or should I be concerned?