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thumper_calgary

One valve way out of spec?

9 posts in this topic

Hey All,

 

First time doing this and I though I would consult with the experts....

 

Checking the valve clearances on my 03 WR 450. Everything is pretty close to spec except the left side intake valve is at about 0.30mm. This seems odd to me that one valve would be that different? The "feel" with the feeler gauge is a bit different too. I can't tell if that's because I'm using a thicker gauge and it's just flexing as it slides under the cam lobe or what. It seems tight from about 0.13mm up to 0.30. I'm not forcing them under by any means.

 

Here's my question. Is it possible that one valve would have a much larger clearance than the others? doesn't the clearance get smaller as the engine wears?

 

Thanks

 

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Doesn't sound right

Clearances get tighter, not wider, with normal wear

 

Clearances getting bigger can be due to bent valve, or a piece of carbon jammed between valve and valve seat

If the clearance really is 0.3 then a 0.13 would have no resistance whatsoever

 

Photo's?

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I'm going to tear the head down today... I'll post up what I find. The bike runs perfectly though so I'm not sure what could be up.

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Two possibilities spring to mind.  One is a galled cam cap (which CAN be repaired, BTW), and the other is a failed valve stem tip.  The tops of the stems are hard capped, and that sometimes shatters off the top, leaving a suddenly very large clearance gap.

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I pulled off the head and brought it into the dealership so the tech could look at it for me. He figures it's a mushrooming valve stem and the camp lobes are wearing a bit. I tried to take some pics but they didn't turn out very well- I'll try again later. you can see the pattern of layers wearing on the cam lobe.

 

Anyways the upshot was that he says shim it and ride it. he also advised against using the Hotcams shims as they are sintered and wear your valve stems and buckets more quickly. he said he'd only ever use OEM shims in any of his bikes.


If its not broken, ride it! Oh! Just checked weather for Calgary, sorry.

yeah I went to drop my suspension off for revalve and it was literally a blizzard. cars stuck everywhere, major highways closed... got a heater for the garage thought :)

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Cam lobe wear will not affect valve clearance.  Why?  Simple: the heel of the cam, where clearance measurements are taken, never contacts anything, and doesn't wear.  Only the actual lobe itself wears.

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Cam lobe wear will not affect valve clearance. Why? Simple: the heel of the cam, where clearance measurements are taken, never contacts anything, and doesn't wear. Only the actual lobe itself wears.

Right you are! The wear that was affecting clearance was on the valve stem. Wear on the cam lobe is incidental and not related to the clearance issue...

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