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VALVES when to replace what to look for

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I have an 07 KX 450f and since the season is coming to an end I've put many hours on and am due for a top end service over the last 50 hrs I've had to shim her ever so slightly 2 times. My question is sure ill replace piston, rings, cam chain, tensioner but what about valves,springs,guides,and seats I really have no clue what to look for do you guys just throw the piston rings tensioner and all that good junk in and call it a day or should I pull the head off take it to a machinst and have em look at it any help would be appreciated just dont have a clue what to look for.

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The first time is considered a impending warning. The second time you have to shim them, it is time to replace them.

Sorry for the hijack OP but this seems like the place to ask since its on topic.

Why is this? Could you elaborate a little? Im just curious as I just bought a used 450 and have no idea about the history of the valves. I pulled the head just to check things out for peace of mind an sure enough they are well within spec. after being shimmed by the shop (I have reciepts to validate this) but Im worried after reading this.

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I am curious and worried as well since I have shimmed my 450 4 times on the intake side. Exhaust once.

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The concern is that if you have to adjust the valve clearance a few bad things could be happening. One: the valve could be streaching and will eventualy break off, two: the hard coating on the valve could be wearing and the valve will start cupping against the seat, and three: the valve seat could be wearing causing the valve to sit deeper and deeper into the seat.

All are signs of a worn valve train.

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The concern is that if you have to adjust the valve clearance a few bad things could be happening. One: the valve could be streaching and will eventualy break off, two: the hard coating on the valve could be wearing and the valve will start cupping against the seat, and three: the valve seat could be wearing causing the valve to sit deeper and deeper into the seat.

All are signs of a worn valve train.

Exactly.

The wear factors on these high-performance valve trians can come from just one, or several places, but it WILL come.

Just plan on removing the head, and sending it out to be re-build by a pro.

Then he can inspect the service limits on every part, and make a determination of what needs replacing......

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I've always assumed that once a valve clearance changes, it's the beginning of the end. Something has worn, and the way things work, it never stops.

Which is why I've always thought that re-shimming was like putting pumping more air into a tire with a leak that starts real slow and gets worse. It makes some sense early on.

After 230 hrs I had all four original valves (and guides) replaced.

Can someone please explain this? After another 30 hrs ride time, one of the new OEM inlets had tightened from a loose 004 to a tight 004 thou. Not much but it certainly moved. Remembering the wear on the rims of the old inlets, I guessed the seats were probably not cut right, and so my new valve rim had been damaged quite early. But with another 40 hrs, that valve has stayed at a tight 004 thou. Inconsistent with my original statement. What could be going on??

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