I agree with Pat the motoman. always have "broken em in like you want em to ride", but there is one big caveat that no one has addressed, and I'd like to see what Pat thinks- he quotes, "The other factors that have changed are the vastly improved metal casting and machining
technologies which are now used. This means that the "wearing in" of the new parts
involves significantly less friction and actual wear than it did in the distant past."
this does not really apply to a cheaply made chinese engine whose design is stolen from a russian WWII era scooter engine.