Camshaft "cover" scratched


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.

Did he (or anyone else) ever adjust the valves and have to remove and replace that cam? My first guess would be that someone didn't use a torque wrench (or a torque wrench that wasn't calibrated) when they bolted that cap back on and bolted it on too tightly. I could be wrong, just my initial guess.

In regards to a fix, there have been other people on here with similar problems and some machine shop has apparently been able to fix them. I don't remember the name of the place but search the threads and you will find it. :cry:

I have an identical bike and will now take mine apart to check for similar symptoms.

Thanks for any responses.

Anssi - Mike at Engine Dynamics does a really nice job of repairing these.

The most commmon cause I've seen for this is excessive torque on the cam caps during reassembly, uneven tightening of the cap bolts and not having the cam turning free when the cam caps are reinstalled. It's common to have to tap the cam side to side to find a good fit that allows the cam to spin free while reinstalling the cam caps. Failure to have the cam turing free tends to gall the bearing surface of the cam cap. SFO put it best a while back when he said something along the lines of they are the only plain bearings in the entire engine and they deserve respect.

Thanks guys.

I'm pretty much positive the problem is due to overtightening.

I have to consider my options about the repair/replacement. I think I might be able to find someone to do a good job of it in Finland.

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