2006 Engine Build

Hello all I just bought a new yz450f and I got it in peices, I have a head that the previous owner, recently had redone by millenium. For some reason he have taken the valves out (I'm guessing because the intake cam seized.) Anyway I sent the head to Engine Dynamics and has the intake cam journal bored and now I'm left with trying to put the valves back in.


The "other guy" put all the valves and springs and retainers in the same bag. I know which valves are the exhaust valves but I can't spot any distinct differences in the intake valves. Is the middle valve supposed to be slightly longer than the other two?


The next problem is differences in springs how to tell? I've visually inspected them but can't spot the differences. Where should I use a micrometer to tell the difference?


And keepers I have a pile of them are they all the same intake to exhaust? As well as the retainers?

Any help is appreciated.



The center intake should be slightly shorter than the outer two.  The retainers and the keepers are in two sets, intake and exhaust, so there will be two alike and three alike.  The exhaust stems are slightly larger than the intake, so you can separate the keepers by which stem they fit properly onto. Springs are also in two sets.  Look for differences in wire diameter and coil count to match them up.  The exhaust springs are stiffer, so should have slightly fewer coils or slightly larger wire. 


Technically, the lifters really should not be mixed or moved around in the head, but there's no way to tell one from the other except for the left exhaust, which will have a different wear pattern because of the action of the auto decompression pin.  The concern is not so much the fit in each bore, but the interface of the lifter with the cam.  But there shouldn't be a problem as long as it's all in good shape.


But here's your big problem: which valve, other than the center intake, goes where? If you do not replace the valves and cut the seats, you have a potential for a mismatch that could lead to some trouble.  You may need to take your best guess and then test the seal by filling the port with solvent to see how well it holds, then try the valves in the opposite position.  Install them where they seal the best.


Also, when reusing valves, look at the faces where they seal to the seats.  There will be a contact stripe on the face that can tell you how worn the valve is.  A contact stripe that's blotchy and irregular looking like the valve in the foreground below is acceptable and in good condition.  A bright metal colored stripe all the way around, and/or ANY trace of a wear ledge like the other valve has means that the hard coating has worn through and the valve is worn beyond usability.


NEVER EVER EVER lap titanium valves....ever.



Well these are brand new valves, he had the he's done by millennium and then he tightened the cam caps too tight when he was putting it together and scarred the intake cam journal. He then took it apart. I bought it at this point. It had new seats on the head and the valves look to be new and he said they are as well. From what I know he had a 1/2 a mile on it before the cam chain skipped because of the cam journal and then quite a lot of starting and having it die.

Coild putting solevant in the ports cause and damage to the valve seal?


So here are my lengths and dimensions.






The Other guy had them labeled but he didn't remember where he started counting at. So he said #2 was the middle intake valve.


Valve Springs







What would you suggest I do?

I can tell the difference in retainer and keeper just by looking at them. The exhaust are bigger.

According to the manual all of those valve springs are sacked out and shouldn't be used. Min. Is 1.42" intake and 1.44" on exhaust. Are they oem components?

I don't think so, I think they were aftermarket. OEM has marks on the exhaust valves. I just went down to the dealership and bought some new springs so now I'm going to try putting it together. I'm still not sure what to think on the intake valves. Gray said the middle one should be slightly shorter and my valves are all different lengths.

Are the valves stainless?

Titanium. I put the valves in with new springs and then leak tested it and the valves don't drip solvent but they do wick moisture on the bottom side of the valves so I think I'm going to lap it as per the manual.




Never mind after seeing multiple warnings not to lap titanium valves I'm passing on that for now.

Edited by sledtrash

The center intake should be right at 3.1" tall from end to end, and 2.9" from the bottom end to the top edge of the keeper groove.

So When I was trying to shim the valve clearance I found out that the one valve was too long without any shims to even adjust for I switched the #2 and #3 around and everything worked as it should I was able to shim the valves and they were all within the specs in the manual. I got it together this afternoon and took it for a short ride. Everything works as it should and the bike runs like a champ. Thanks gray for continually allowing myself and others pick at you knowledge.

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