is it normal for a valve to change slightly in clearance during break in? i have a 2007 yz250f that the center valve was near to tight from the factory and then it tightened after engine break in at 25 hours. very very little it tightened. tightened just enought that i couldnt get the feeler gauge under it but the next feeler gauge down was very loose. i shimmed it and there are no signs of it moving. is there a chance the engine break in was the cause of valves to seat and change and tighten slightly? or do i have a defective center intake valve?