I've searched this before, but would just like some confirmation. I have a 2006 YZ450F. Last year, the top end started getting noisy. Valves were OK, but re-shimmed since then. Decided it was the cam chain worn, so got a replacement from Rocky Mountain, since I read that the OEM chains could stretch. I am second guessing myself now, but I thought at the time that the noise was gone, and it sounded normal at the start of a 80 mile ride, first time out. By the end of the ride, it was back again. This was in April, and since it has gotten progressively louder. I have a 2001 426F that I recently re-built, and it has no top end noise. The 2006 is downright obnoxious. I pulled the flywheel off and the valve cover, and cannot see anything amiss. Probably have 500 miles on this new cam chain. Is it possible that it just stretched in that first 80 miles? I did not replace either guide, as they looked OK, nor the tensioner, as it appeared to be OK. Should I just try a new cam chain, or should I do the whole bunch; both guides, tensioner, and chain? I supposed it's possible that the chain was just an inferior product, and stretched, but that seems odd. By the way, the cams rotate smoothly; no binding. The guides also look OK, but perhaps a little wear is enough? Suggestions welcome.