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WR426 valve adjustment

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Hi all,


I have been going right through my bike recently (2002 WR426F) to check

everything is all good ready for a bit of track work and all was looking good

until i come to checking and adjusting the valves...


Both 2 exhaust valves were nicely within spec as was the LH intake valve, but the

middle and RH intake valves were extremely tight (couldnt fit the thinnest feeler

guage in 0.036mm)

They currently are running 1.40 shims in both center and RH intakes (tight ones)

and a 1.65mm shim in the LH intake (in spec) valve.

I have put my numbers into a valve shim calculator and it has come back saying I

need a 0.8mm thickness shim to correct the 2 tight valves but looking at valve

shim kits online they state the thinnest they have is a 1.20mm


So my big question is any thoughts on the huge variation between intake valve

readings and would needing such a thin shim to correct the valve clearance

mean the valve seats are too far worn into the head?


Sorry for the long read hoping someone can shed some light on this for me

Thanks in advance !!!

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I am assuming you have OEM Titanium valves?  


From my experience with the WR426, OEM valves typically wear pretty evenly until the coating on the valves is gone, then they wear extremely quickly.  Once the coating is gone, you need a new valve.  I would personally remove the valves and inspect the back side of the valve where it contacts the head, and the head itself.  I'm going to guess you are ready for new valves.


Take some pics and post here if you are unsure whether the wear pattern is acceptable or not.

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Thanks heaps for the fast reply

I have since pulled my head and removed the suspect intake valves only to find that they are totally cactus!!

They have a large indent cut into the mating surface of the valve but on the bright side though the valve seats

look in very good order so it seems the valves being alot softer than the head they have taken all the beating


I have done alot of research of parts fiches and have found that a set of genuine 2000 YZ426 valves (stainless, pre titanium) will fit my

'02 WR426 with only the need to change valve springs to suit the stainless valves, spring retainers and collets all the same part no.

between the '02 WR (stock ti. valves) and '00 YZ (stock stainless valves)


I have been told that it is not possible to lap in ti.valves due to the hardened coating on the valve so would it be possible to lap in a stainless valve or

does the seat still need to be cut?

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If you went to all the trouble to pull everything out why wouldn't you have the cyl head and the valve seat machined to be a perfect mating surface vs trying to lap it in?

What is the advantage of stainless vs the Titanium?......why not stick with stock and avoid potential problems?

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