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motoman393

Valve clearance shims...

12 posts in this topic

Hey guys,

Tonight I checked my valve clearances for the 3rd time since I have had my 01' YZ426 (since Nov. 15 00') and my intakes were all .102mm and the exhausts were all .203mm. This is VERY close to being out of spec, and I am for sure going to have to adjust them in the next 5 rides or so. And I was wondering a few things:

What is the stock shims sizes? I have heard that the shims are diff. for each bike manufactured? I want to be able to have the new shims ready when I take the cams out to adjust the valves so my bike wont be torn apart for 1-2wks waiting for the parts to come in. Is this possible? Is there any place cheaper to buy shims than Yamaha ($5 for a shim that is ridiculous...I can see $1-$2 a piece). Thanks,

Garrett

------------------

I get my kicks on a 426!

Motoman393's MX Site

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Mine came with 175's all around. I had to shim one valve last time and I'm sure the other 4 will be getting new shims next time I look at them. I wasn't out of spec yet but it wasn't too far from it. Also, I would have the shims in hand before you tear it apart as all the dealers around Sacramento didn't have any in stock. Couldn't believe it...

Pat

99 YZ400

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How the hell would they be able to do a valve adjustment for a customer if they didn't have the shims in stock? Makes me wonder what they do when you take it in for that service.

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My '00 had different sizes at each intake valve location and they weren't rounded to the nearest .05. I could have had one stamped 179 (1.79), for example). If special ordered, they may be only available to the nearest .05.

I went to Berts (SoCal) and they had a box under the counter with all sorts of sizes (thickness) that they had taken out of customer's Yamaha four strokes (street and dirt). In other words, they charged someone 5$ for a shim and then sold me his used shim for 5$. :) They've really got something going there.

Although all three intakes needed adjustment (very slightly tight), I was able swap two and buy one. It's been about 18 months, so I've just checked them again and found them to be well within specs. If anything, they've loosened slighly, so maybe I shouldn't have adjusted them. Your measurements would have been out of spec on an '00, so I assume that an '01 has different clearance requirements. Those that have much more four stroke experience that I (that's not too hard) claim that a tight clearance is more critical (bad) on the exhausts than on the intakes.

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Holeshot's Page

[This message has been edited by holeshot (edited September 30, 2001).]

[This message has been edited by holeshot (edited September 30, 2001).]

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When the engines are assembled at the factory, the valves are adjusted using whatever shims are necessary. The range is pretty close engine to engine but there is some variation since no two engines will be exactly alike. You will have to remove the cams to see what shims are installed before you can know which ones to order. It would be great if you can go down to a dealer and swap the shims you need to change out for ones that bring the valves exactly where you want them instead of having to accept shims in .05mm increments. When I checked mine, I had two shims at 1.78mm and three at 1.80mm.

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Ooops :), Looks like I messed up on my decimal location (edited).

The clearances are different from the '00 to '01.

'00 are as follows

Intake: .15mm - .20mm

Exhaust : .25mm - .30mm

I would guess the difference (.05 less for the '01) is because of the titanium valves used on the '01.

I don't have my materials book handy , but it appears that titanium has a lower expansion rate than the material used for the '00 valves (stainless?). The smaller clearances are another advantage to using titanium.

------------------

Holeshot's Page

[This message has been edited by holeshot (edited September 30, 2001).]

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The specs that you are at are great! The closer you are to the small number, the more power the bike will make (valves will open sooner, close later), and the quieter it will run (less slop). As far as shims, when they assemble them at the factory, if neccesary, they will put "half-sizes" in the bike. In other words, these are shims you can't buy at a shop (and won't find in the shim chart in the manual), and they are the ones you want to hold on to.

What was the question again?

------------------

Josh

01' WR426

99' YZ400

87' FZR1000

Uh, like twist the throttle...

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If you need thinner shims real quick line yourself up with a good local machine shop. They can easily surface grind off a couple thou's to make them right. I do them myself and finish them off on fine, wet paper.

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Hey motoman I am in Houston as well. I have a '01 426 that I bought about 3 months ago. Probably has about 20 hours on it. I have never checked the valve clearances. Is this difficult to do? I have talked to some guys with older 426s and 400s that have never checked the valve clearance on their bikes with no issues. Is it really neccesary, I keep getting conflicting opinions? What is a good shop to take the bike to and have this check done if required?

Originally posted by motoman393:

Hey guys,

Tonight I checked my valve clearances for the 3rd time since I have had my 01' YZ426 (since Nov. 15 00') and my intakes were all .102mm and the exhausts were all .203mm. This is VERY close to being out of spec, and I am for sure going to have to adjust them in the next 5 rides or so. And I was wondering a few things:

What is the stock shims sizes? I have heard that the shims are diff. for each bike manufactured? I want to be able to have the new shims ready when I take the cams out to adjust the valves so my bike wont be torn apart for 1-2wks waiting for the parts to come in. Is this possible? Is there any place cheaper to buy shims than Yamaha ($5 for a shim that is ridiculous...I can see $1-$2 a piece). Thanks,

Garrett

------------------

Chopperman

00 KTM 520 EXC

01 Yamaha YZ 426

78 Yamaha TT 500

78 Yamaha SR 500

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Chopperman,

Yes you NEED to check the valves on the YZ often...very often! If the valves are not checked often you run the risk of MAJOR engine damage. Checking the clearances is easy it takes around 30 mins and the only "special" tool you need is a set of feeler gauges that are the right size for the application (.10-.25mm)

After awhile valves tend to drive deeper into their seats (they become tighter). Whenever they are tight your bike will run sluggishly, will not rev as quick as it should, and will most likely not hit the rev limiter.

I try to check mine once every 3-4 months. I ride my bike very hard 1-2x a week and I have had it since Nov. 15 00' and it is just now due for an adjustment. Generally the YZ needs an adjustment once a year since the valve drain is a shim bucket design and has no rockers (and is very durable)! Hope this helps,

Garrett

------------------

I get my kicks on a 426!

Motoman393's MX Site

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