Hi, My dad has a -03 YZ450 with about 100 hours on it. He wanted some head work done, so I helped him take it apart. The part that holds the intake camshaft in place has scratches in it(at the bearing surfaces where the camshaft touches it) that you can feel if you move your finger over them, almost as if it had reached melting temperature. The exhaust side is fine. How the hell did this happen? The oil filter and oil has been changed regularly(every six hours). I don't want to fix the symptom before I know what caused it. Oil pressure problems? The ball bearing going bad causing the camshaft to move around? To make matters worse, Yamaha only lists this cover as part of the complete head assembly, for about $600. Any way of machining the part back to working order? I have an identical bike and will now take mine apart to check for similar symptoms. Thanks for any responses.