This seems too simple, but I have to ask. I am about ready to have my cylinders bored and rave valves shaved, I am confused. There was a warning label that came with the piston that stated that If the pistons are .020 of more over stock that the rave valves need to be shaved .015. Mine are .020 over. I do not know why you would shave them more then the change in clearance which would be .010. What am I missing?