Getting the right valve shim


3 replies to this topic
  • ivesy

Posted March 27, 2008 - 08:52 PM

#1

After checking my valves, I found one intake was .178 (should be 0.2-0.5). I removed the shim for this valve and it was 181 (1.81mm)
Now following the chart in the manual the shim I should replace it with is a 180. This wont even bring it back into spec so I'm thinking I will put a 175 in anyway. Has anyone else found this?
Also three of my other valves were right on the limit, should I re-shim these or just keep an eye on them?

Cheers

  • grayracer513

Posted March 27, 2008 - 10:22 PM

#2

The clearance figures you quote don't add up. If it is an intake, the clearance should be .10-.15mm. If you have it at .178mm (.007"), it is too loose, not too tight. Are we talking about an exhaust, perhaps? Or is your mistake elsewhere?

The shim you found is an OEM factory assembly shim. Yamaha uses shims in .01mm increments when they originally set these heads up. It's not at all unusual to find 5 such oddball sizes installed.

Let's assume it's an exhaust, and that it measures .180 (I'm rounding because no one is ever going to be able to tell a difference of .002mm with a feeler gauge) You have a 181. A 180 will not restore it to spec, so you use a 175. 181 - 175 = .06, .180 + .06 = .24 mm. Spec is .20-.25, so you're good.

Be sure to recheck this valve again after one or two rides to see that it is holding clearance. If it isn't, you need a valve job.

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  • ivesy

Posted March 27, 2008 - 10:39 PM

#3

Sorry yes your right, its a exhaust not intake. I just thought it was weird that following the table in the manual gave me a 180 instead of the required 175 shim but I guess the rounding has something to do with that.
Thanks for the tip, I'll re-measure that valve after say 5-8 hours.

  • grayracer513

Posted March 28, 2008 - 08:43 AM

#4

I just thought it was weird that following the table in the manual gave me a 180 instead of the required 175 shim but I guess the rounding has something to do with that.

The table only gave you the wrong shim because of your interpretation of it. The table does not list a 181 shim pad, only those in the standard .05 mm service shim increments. In the situation where you have a non-standard OEM build shim, some math is always required.

In your case, you had a choice of 180 and 185, and apparently made the assumption that if you had a bigger shim than the 180, you needed to use the next larger column, when in fact, you needed to stay with the size closest. It would have gotten trickier yet if the bike had a 182 or 183 installed, but even then, penciling the thing out will give you the answer.





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