It would appear that I damaged the valve seals on my 06 YZ450 . Has anyone had any luck changing these with the head on? I remember reading about pressurizing the cylinder and then removing the springs and keepers. But I am a little doubtful about being able get to all of them on the bike......? Anyone had any experience with this?


Thanks!

I know that it's been done, but the guy who did it was an experienced tech and had to fabricate a tool for the purpose.  I'd only advise such a thing for someone who was both very experienced and very determined.  And very patient.

Would probably save a lot of headache to just pull the head.

 RiderX, on 29 May 2012 - 05:46 PM, said:

Yep, you're right just did.

I pulled the head, the cylinder looks good. One of the valve stems does not seem to be sticking up out of the retainer as much as the others (this one was way out of spec). Is this something I should be concerned with?  I have not pulled the valve yet so I don't know what the stem looks like, is there anything I should be looking for other than any obvious scoring?


This my first time doing valve seals so any advice is greatly appreciated!

Well for the most part the valve stem seals are pretty reliable if the valve is way out of spec and the seal position seems wrong take a close look at the valve seat in the head and the valve guide if the motor has gotten hot it's possible there can be issues with these parts moving in a bad way.

 Slow and Jerky, on 30 May 2012 - 04:51 AM, said:

There could be two reasons for that.  One would be that the keepers ("collets") are shearing and moving up on the stem, and the other is that the top of the valve stem is worn.  In the latter case, the valve should be replaced.

 grayracer513, on 30 May 2012 - 06:48 AM, said:

If I do need to replace the valve, is there some way to determine if it is stainless or titanium? I bought the bike used and the bottom had been redone at some point before I got it.

Yes, but it's more of an art than a science, and difficult to describe to someone how it's done by inspection.  One way is with a grinding wheel, but you'd need to have seen this done to both materials (and saying "stainless steel" is a little like saying "plastic", there's a lot of different kinds).  Another, easier way is weight.  An SS valve will weigh from 1.5 times to nearly twice as much as Ti.  But of course, you need one of each for that.

I pulled the valve in question, I don't see anything obvious, but I here is a picture:


https://docs.google....aVNBM2NpQW9hSm8

Thoughts?

 Slow and Jerky, on 30 May 2012 - 04:05 PM, said:

Well I typed too soon, I went ahead and pulled the other valves and it appears that the one in the picture lost the tip of the stem. The other four have what looks almost like a shim on the end (but still part of the valve). So now I need to figure out if these are stainless or titanium.........

 Slow and Jerky, on 30 May 2012 - 04:48 PM, said:

What's the reason for the concern?

I am assuming that I can replace just the one valve, but would not be a good idea to mix them. I did get ahold of he former owner and he tells me that they are OEM valves. So if I buy a new valve can it be installed without having the seat redone?

 Slow and Jerky, on 30 May 2012 - 06:50 PM, said:

Absolutely not.  Unless you don't care how long it lasts (or whether your engine randomly explodes one day) the seat MUST BE refinished.  The new valve is perfectly round, perfectly concentric, and at the perfect prescribed angle.  The seat is something less than that.  The better the seat is finished, the better the valve will seal, and the less wear will be required on either the valve or seat to match the two up.  The accuracy and finish is of paramount importance with respect to the longevity of the valve.

NEVER lap a titanium valve, no matter who says what: http://www.wiseco.co...alveInstall.pdf

There's no real problem mixing SS and Ti valves in the same engine, even when you're mixing one set or other, like just the intakes versus all the intakes or all the exhausts.  The one thing you have to be certain of is that the appropriate springs are used for the type of valve in place.  Springs intended for Ti valves are apt to fail in controlling valve float at high RPM with the heavier stainless valves, and springs for SS valves would be too hard on the lighter Ti's.  Since you're using OEM valves, replace all 5 springs with new OEM. Cheap insurance if there ever was some.

Thanks for the advice, I suspected it was going to be something along those lines. Just out of curiosity, what do you suppose could have caused that valve to lose the end of the stem like that?