CCO valve adjustment
 

My CCO has a slight "tap" when the engine warms up. i was going to adjust the valves but according to the service manual, the only thing you can do is grind the valves if there is not enough clearance or replace the valves if there is too much clearance. is that true, or is there anything i can do to adjust them? if the timing is not 100%, will that create a tapping noise when the engine is warm. it is not hard to start, and i have never had it backfire before. thanks:American Flag 1: