valve clearance example!

1 reply to this topic
  • mstangsteve

Posted October 08, 2012 - 07:24 PM


Intake clearance spec 0.10-0.15mm
Intake valve 1
clearance 0.051mm
spacer under cap= 1.85mm
correct spacer under cap = 1.76mm to make clearance gap aprox 0.14

Is my math correct? Im trying to correct the valves on a 2003 yamaha yz 450f. It recently installed an athena 480 big bore. what clearance should i shoot for? intake spec is 0.10-0.15 and exhaust 0.20-0.25

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  • grayracer513

Posted October 09, 2012 - 06:58 AM


If you have a 176 shim available, that would work in the example given yes. 176 is a size that you would only have if it came new in your bike or some other one. Service shims are only available in increments of .05 from Yamaha. Honda and the aftermarket make shims in increments of .025 (a 1.775 shim is marked 177 or 178, usually). Yamaha has shims for use at the factory in .01mm steps.

Your clearance is 0.051. Rounding to 0.05 (.001 mm is .000039", and far too small to be measured with a feeler with any accuracy), you subtract the clearance you have from the correct range:

.10 - .05 = .05, and .15 - .05 = .10 giving you .05 and .10 mm as the amount of correction needed.

Since the clearance is too small, you have to correct with a smaller shim, so:

185 - 5 = 180, or 185 -10 = 175.

The standard service shims would yield either .10 or .15mm clearance, either of which is in spec, and therefore OK to use, although .10mm is preferable. In your case, the 176 falls between these two sizes, and since it yields a clearance of .14mm, would be a good choice.

Always try to get near the smaller of the clearance specs without going below them. It's easier on the valve train. Remember, though that the difference between the high and low is only .002". Don't stress out about getting to an exact number within that range.

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