I put a used 99wr400 motor into a 99yz400 bike and ran it up and down the street once and dumped the oil out of the frame reservoir bolt hole it came out dirty black. The oil out of the motor drain bolt hole come out clean, like new. And the filter area had clear cleanish new oil with the usual debris . I'm sure something is wrong because I'm of the opinion that after a few minutes running all oil in the motor and frame should have mixed and be about the same in appearance. I put a hot cam auto cam on this motor and an 06 yz450 carb and it runs great but I'm not sure what to think about the dirty vs clean oil situation? right now I have a new oil filter in it and new rotella t oil but thought I'd get other thoughts on this situation before running it any more.