This is a re-post / update.... I have a "problem" with my '06 XR650R. The rear sprocket has a "high spot" which cases the chain to have variable tension. The chain / sprockets are brand new (3rd new chain) RK GB520GXW Sprockets are Renthal 15 / 45 I have replaced the chain and sprockets once before, thinking that the old chain had crappy links and / or the Sprockets were defective... but it still did it. The problem is that although the runout on the sprocket is only about 1mm it causes a 5mm difference in chain tension between the "loose" side and 180degrees later the "tight" side resulting in "chain slap" this slap is causing the chains to sound real crappy after less that 2000 miles (hence the third chain in 4000 miles) This gets expensive. It does not matter what sprockets I use, so I'm tempted to say that the hub is defective, but when I checked it, it seems to have no runout etc.. but put a sprocket back on there and the runout re-appears. (at the same location) There is a tiny (1mm) gap / play around the large raised portion of the hub that the sprocket fits around and after tightening on the sprocket, the first bit of torque "repositions" the sprocket off to the one side by a fraction. This is the only area that I can find any variation, I am taking the bike back to the dealer to have this checked out next week. BTW the bike is DS'ed and gets used mainly on the road and in not subjected to what it's designed to endure, so I'm a bit miffed about all this crap...... does anyone have any advice please?