When changing shims, are most setting to the big end of the clearance range, or to the center? My experience with other in-line 4s, and research in general all points to the large end of the range being the best target, and wondering what the consensus here is.
Valve shims
- Thread starter ScottMDMC
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Well, the spec range is only .07mm (0.15 - 0.22mm Intake, 0.18 - 0.25mm exhaust). If you are using the standard 0.05mm increment shims you have no choice which end of the spec range you will be in. Only one selection will put it into range and the next size will put it out. If you are able to acquire some shims in .025mm (half size) increments you'll be able to pick from two different shims.
The advantage of leaving the clearances on the wide end of spec is that as the seats wear over time you will be less likely to require a re-shim again. This is especially true of the intakes, which (counter-intuitively) seem to close down faster than the exhausts. It may be that the exhaust seats are protected by the carbon deposits, or that those seats are actually harder.
Because I sanded my old shims down, I was able to target the 70th percentile of 0.20 for the intakes. That bike is coming up due for another valve check in another 5k miles, and it will be interesting to see how things have settled 25k miles later (100k total). However, I don't know how long it will take my son to put those miles on the bike since that bike is now his.
The advantage of leaving the clearances on the wide end of spec is that as the seats wear over time you will be less likely to require a re-shim again. This is especially true of the intakes, which (counter-intuitively) seem to close down faster than the exhausts. It may be that the exhaust seats are protected by the carbon deposits, or that those seats are actually harder.
Because I sanded my old shims down, I was able to target the 70th percentile of 0.20 for the intakes. That bike is coming up due for another valve check in another 5k miles, and it will be interesting to see how things have settled 25k miles later (100k total). However, I don't know how long it will take my son to put those miles on the bike since that bike is now his.
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On my previous machines, looser valves resulted in both slightly more noise and a definite increase in mid-range torque. Not really worried about more mid-range, but if I can get both safer operation and more power, seems like the answer -- though I do get that the range is a tad less than 3 thou.
rbentnail
Economic Plankton
You must be new here....there's no such thing as a consensus on this forum. One thing for certain tho:
in spec good, out of spec bad.
Don't overthink it. As mentioned above there's not a lot of wiggle room unless you customize your shims. Hopefully you aren't that anal
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ApexGT
Well-known member
Error on the loose side, tight is bad
RaYzerman19
Go Wings!
If you use Yamafitter's spreadsheet, that uses the 70th percentile and will calculate the shim you need. From all the shim changes we have done, we've removed mostly .185-.188, swapped a few around, but if buying shims, buy smaller than that. I can't recall us using anything below .170
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rbentnail
Economic Plankton
No. No it's not. "Out of Spec" is bad. Anything "In Spec" is good. "Tight" has nothing to do with it.
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I aimed for loose when I adjusted mine, getting them all well within specifications, but on the loose side. I also noticed more noise, which bothered me enough that I tightened them up just a little bit.
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