I am in the process of checking/adjusting the vavles on my new to me 2000 xr650r with unknown history. While rotating the flywheel (counterclockwise) I am hearing a loud metallic tap or click coming from the right side exhaust valve just before it closes. No other valves are affected. I can feel something hit the valve as I put my finger on the adjuster nut while rotating the flywheel. O.K. I just checked the valve and it was extermely tight (couldnt fit the feeler in at all .008mm) I rotated the flywheel while the valve adjuster nut and valve was way loose and the noise went away. I can supply more info if need be. The bike runs well, but I can remember hearing a metallic clicking noise, on my last ride. So the question is, will a tight right exaust valve cause this noise, and did any damage occur (opinions) riding with a valve so tight (50 100 miles)? I understand the decompresser can affect the clearance so I will take pains to be sure it isn't part of the problem.