I know this has been stated many times but after this weekend I want to be sure it is reiterated once more. CHECK YOUR SPROCKET BOLTS!!!!! After a 2 hour practice on Sunday I got hame and was cleaning my '06 YZ450F and every bolt on the sprocket was not only loose but about to fall out. Made some nice oval shaped holes in the stock sprocket. Needless to say I will replace the sprocket and now loctite the bolts but be sure to check yours also.