yz400 Valve Adjustment

I have a 99 yz400f I am going to be doing a valve adjustment tomorrow.I have never dealt with the bucket and shim style.My question is can I use the old shims? I have read to put new ones in it to make up the difference in the adjustment..Can I get by without them? I have a race sat and dont have the time to wait on new shims and cant get my bike to act right so Iam going to check the valves.Can I get by with the old shims that are in it?

typically valve jobs are a normal service that every dealership should offer, which means that somewhere in that beautiful factory shop they oughta have a shim kit.

get your measurements, remove your shims, check and see if any of the removed ones work for the others, and bring them to the dealer. He should swap them for you without a problem.

pretty much standard operating procedure. Hope this helps. Don't forget your in/lb torque wrench.

so your saying the ones that are in it now will not work again? I was hoping to get by without running as my local shop is 40 miles away..I have a manual and its whats saying new shims

If its out of adjustment the old shims wont work. They are different thicknesses

What i meant was, check the number on the old shim and/or use a micrometer to verify it. If it is the correct size to put one of your other valves into spec then use it.

I do not have a mircrometer...Will I be required to have one to do a valve adjustment?I did a valve adjustment on a 400ex I had and i can tell this is a whole new ball game. I have never dealt with the bucket and shim style valves.Thanks for your advise

doesnt your manual tell you about how to do this? The shims have the numbers on them

doesnt your manual tell you about how to do this? The shims have the numbers on them

But most of the time, on a bike that old, the numbers may not be readable.

I suggest you check the clearances first before you worry about this detail. You may not need an adjustment.

Ok another question...I am getting smoke on my startup overnight so I assume my valve seats/seals are shot..In my manual it reads I need valve compressor and installer to do so..Can I get by without buying the costly tools??I figure I can buy a new set of seals and shims and that take care of my job??Also will I need a new valve cover gasket or can I also get by without that...Iam on a very tight budget so everything I can save is great.

Also will I need new valve seats and valve stem seals?? I am not sure but can I just get the valve stem seals and cure the oil leakage

Seals, not seats. The seats don't control oil. And you need a spring compressor. You may be able to rent one from a local rental outfit. Failing that, just take it to a machine shop or bike shop that does head work and ask them to change out the seals for you. Shouldn't cost much.

So I am going to need valve seals and shims for sure...Am I right by saying the the intake seals will be the same part number and the two exhaust seals will have the same part number. I know a fella that may have a spring compressor...Will one for a car/vehicle work with the bike? THANKS grayracer your a big help

OK Quick Update...Got off the phone with a friend of mine...He has a spring compressor and a digital micrometer he is going to loan me for the job...My question now is,To keep from buying an entire shim kit how can I use the Mic to find the sizes I need to just order them separate. I really dont have 60 bucks to drop into a set that I will probably never need again(dont mechanic a wholelot)

OK, back up once more. Start by CHECKING the clearance. Then you will know if you need any shims at all. After that, assuming you do need to change the clearance on a couple of them, you then remove the camshafts and find out what shim sizes you have on those valves.

Let's imagine there are two intakes that that are both at .13mm and need to be opened back up to between .15 and .20 as called for. One has a 180 shim, the other a 185. These shims will measure 1.80 and 1.85mm. Take the thinner 180 and put it on the valve that had the 185, and that valve will now have .18mm clearance, and you will only need one shim, not two. Get it?

You also NEED a torque wrench that you can reinstall the cam caps with.

When looking for shims, go to a Honda shop and ask for shims for a 2002-2009 CRF450. They are the same diameter, and I guarantee they'll have them.

Changing valve seals is not something you will want to try before this weekend. The head has to come off the bike.

OK I sure thank your for your time helping me...I will order what I need Thurs on payday and maybe have everything tore down and ready to put back next week..I have race sat so I will just let her smoke. I saw somewhere the formula how to find the size I need I just cant seem to find it...Iam pretty sure I understand what you mean though and sure thank you for your help...AM I forgetting anything in particular...I would go ahead and freshen things up but Iam a broke man lol. I was wondering how the valve seals would have worn like they did the top end looks like brand new,still shiny and everything. I do know I overfilled it with oil last week because it was so clean and didnt realize it until i checked it after it smoking,Would that have been the culprit to ruining the valve seals...Iam almost positive its just the seals because it clears up completely after about 30 secs and sometimes dont do it at all....Its kinda embarrising at the track with the 4 stroke smoking lol so I need to get this fixed asap....I am starting to miss the 2 smokes lol MUCH more simple but I do like my YZ just wished these unexpected probs wouldnt keep popping up...The guy I got it from said it had sat for 7 years in the storage building I got it from and I have had to replace water pump seal,oil pump seal,and fork seals. I guess due to how long it sat would be why I am having all these seal problems????Thanks once again gray racer

The "formula" is just simple math. Most of the time, the valves will be too tight if they need any adjustment. First, you compare your measured clearance to the specification. If it's too small, you determine what the difference is by subtracting the smaller value from the larger. Then you compare that difference to the shim size that valve has in it.

Go back to the example above:

Measured clearance is .13mm

Spec is .15-.20

Subtracting .13 from .15 shows that the valve is out of spec by .02mm

Since the clearance is too low, we need a thinner shim in order to add clearance.

Shims are available in increments of .05mm. We have a 185 (1.85mm) shim now, so a 180 (1.80mm) will add .05mm more clearance. Will this work?

Current clearance of .13mm plus and additional .05mm equals an adjusted clearance of .18mm. Since this falls between .15-.20mm, it's good.

You might find out when you get in there, that the bike has some odd size shims that don't go by 5's, like a 188, or a 173, for example. These are original factory build shims that were put there when the bike was first built. They can confuse the decision making process a little. For instance, if the valve at .13mm has a 188 in it, a 185 will give you a clearance of .15, while a 180 will leave you with .20. Both of these two clearance numbers are OK to run because they fall within the specified range. But chose the tighter of the two when you can.


Alright...That made things alot clearer for me....Once again THANKS>..Umm While Im at it...When I replace the valve seals the head comes off,I am pretty sure I will but Will I need a new head gasket..I found this entire kit cheaper than just the head gasket alone at bikebandit... here is the link http://cgi.ebay.com/ebaymotors/Cometic-Top-End-Head-Gasket-Kit-YAMAHA-YZ400F-1998-1999-_W0QQcmdZViewItemQQhashZitem19bd545363QQitemZ110550602595QQptZMotorcyclesQ5fPartsQ5fAccessories I know there not oem but wonder if they will be just as good?

Cometic is a good product, yes.

OK I have another question and I think it will sum up my problems.I am going to order the new valve seals and a top end gasket kit(as it is cheaper than just Head Gasket) and I have one more question.Other than the tools I will need to do this is there anything else I will need to do the job?And also my manual reads about lapping the valves???Iam not sure about that part.Is that something that is mandatory or is this a step I will skip in reassembly?? I am still unclear on that...My plan is to order those parts and after my race Sat and then I will take off my valve cover and check valve clearances and if they are not in spec I will find out what size shims I need and just go to my local honda dealer and get the ones for the crf 450 as grayracer said they are the same...After I get the shims needed(if I need any) and then tear on into replacing my valve seals...I have studied the link gray racer gave me and I can handle the work part.I am just wondering now if I have the right plan in mind and if I can skip the Lapping step in my manual...Thanks very much for any help...(newbie to the 4strokes)

Whether you lap the valves or not should depend on three things;

  1. Are they titanium or stainless steel? DON'T EVEN THINK about lapping a titanium valve. You run the risk of cutting through the hard coating. On a YZ400, the valves are stainless, though, so you could if you wanted.
  2. Did you have to adjust them? If not, you should probably leave them alone. If you had to change the shims because they tightened up, then you should think about it. If you had to go more than 1 shim size different on any one valve, it might be time to replace them.
  3. Do they leak? With the head off, pour some solvent in the ports and watch for leakage around the valves. A little seepage is no big deal. Running/dripping liquid is not good.

Whether you lap them or not, remember to keep the lifters, and valves, and the shims, if you have them set already, in such a way that they go back into the same location in the head that they came from. Left exhaust back to the left exhaust, and so on. Springs, retainers and keepers don't matter as much, although the exhausts and intakes are sometimes different.

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