I recently bought a 97 XR650L. It was in good shape and had just under 10,000 miles on it. When I bought it there was a very slight tick in the top end. I just figured it was normal valve train noise for a honda. I changed the oil and filter as soon as i got it home. I have put around 500 miles on it and the tick has gotten progressively worse. Adjusted the valves and the exhaust were pretty loose. Only helped a little, but the noise continued to get worse. I decided to tear into it to see what was going on. The first thing I did was pull the down tube filter screen. It looked good. I then pulled the oil line off going to the head. It looked good as well. I then proceeded to pull the valve cover off. The left exhuast rocker was toast. It was concaved and missing about 1/8 of material. The lobe on the cam for that rocker was wore really bad. The rest of the cam looked fine as well as the other rockers. What would cause just one rocker to go? Maybe it wasn't hardened correctly at the factory.