I have done all the searches about this but not really sure what my answer is so I am sorry if the answer is out there and I just didn't find it. Our 450 has 78.7 hours on it change the oil every 2-3 hours with Moterex CrossPower 10w50. We use a SS filter and it is cleaned with brake clean and blown out with air form the inside every change. About two oil changes ago the oil started to come out very black, up until then it would just be a little darker brown than when it went in. It was on the original clutch and top end and is raced by my son who is a top intermediate rider. I have been racing for the last 37 years, 30 as an A rider, and have always done my own maintenance. At first I thought the problem might be the clutch, he has been known to go through them before. I took everything out and while they looked good, no sign of overheating or anything, they did measure close to the service limits. I put in a new clutch, all plates and springs, and since then he raced once at Southwick and two practice days at Mototown for a total of about 2.5 hours. While he was practicing there seemed to be a lot of clutch fade. I attributed it to the track being sandier as they brought in some more to cover the track. I changed the oil and again it was black. There were also more metal particles than normal in the filter that I figure are probably due to the new clutch in a slightly grooved basket. The bike still starts first kick and runs great. I had planned on doing a top-end anyways, this will now be his practice bike, so I figured I would just go ahead and do it now. Everything looks good. The left intake was a little tight and will need to be re-shimmed. First shim change since new. No apparent blow-by on the piston that would lead me to believe it could be the cause of the dark oil. I took the clutch out and the steels were blued pretty good. The basket and hub while worn are not excessively so and the clutch had not appeared to be slipping. The crank appears to be well within tolerance and no discoloration. Something seems to be getting pretty hot causing the oil to turn black. We us Fluidyne radiators and EngineIce. We did recently put his complete 08 stock exhaust on the bike but that was after Southwick when the 07 exhaust got all crushed in a crash and also after the oil started to turn black. It appears to be a little rich but not by much. Sorry for the long winded question. Any ideas what could be causing the sudden blackening of oil???? Thanks in advance.