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wr450man

2006 wr450 Exhaust Valve Lifter and Cam lobe damage

8 posts in this topic

I have a 2006 wr450 with 8000km.

During the valve adjustment, we noticed that one of the exhaust valve lifters has a circular pattern of indentations on top, and the corresponding lobe of the exhaust cam has a groove indented in it.

It seems as if the valve spring is broken or damaged and the cam hits the lifter at the wrong place and time.

All other lifters and cam lobes are good.

The valves clearances were within spec, and oil has always been changed regularly with synthetic. And the bikes runs good.

Has this happened to any of you? What did you do and what happened?

Could that be a defective spring on the exhaust valve, since all the other ones are fine?? Can it be a problem from Yamaha?

Any ideas appreciated!

Thanks!

Edited by wr450man

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That should be the valve that is pushed open by the auto decompression pin and those marks are from the pin hitting the cap as it rotates.

Very normal in my experience and should not affect it doing its job. As long as the bike runs fine and the marks are not extremely deep (they shouldn't be) you should be good.

But post pictures to be sure.

Mike

Edited by miweber929

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pics

Bucket looks pretty normal to me, at least the Yamaha 's I've seen have all looked the same.

The cam...hmmm, never have seen that kind if wear, I'll let someone else chime in.

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The wear on the bucket is due to the decompression pin....not the cam lobe. The damage on the lobe is due to the damge on the bucket.

I think the decomp pin may be sticking out and not retracting into the cam. Once the engine reaches a certain RPM the decomp pin should retract...looks like yours is not.

I'd say you need a new bucket and new exhaust cam (unless there is a fix for the one you have).

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The cam lobe never contacts the area of the lifter that has the decomp pin damage, so the odd little spot on the lobe won't be due to that. The cam lobe itself doesn't touch anything outside the lighter colored circle in the center of the lifter. It is also possible that the small center wear area of the lifter is so unevenly worn that it caused the unusual lobe wear. It seems clear that both parts will need replacing in any case.

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Thanks for the help everybody!

So if I understand clearly, the auto-decompressor might be faulty?

What could be worn out?

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