Valve Shimming - which side of spec?

[peterbaron]

...and watching + filming yachts around Auckland waters.

Getting ready to re-shim my valves after 52K miles. Recommended shim sizes (per calc) either put new clearance on low side or high side of spec (IN 0.006, EX 0.011). I noticed, via calcs, that I could deviate from the recommended shim size to push new clearance from low side to high side or vice versa, while still staying within spec range of +/- 0.001. WHY? Because I noticed that the measured clearances historically show the EXHAUST getting tighter (or staying the same) and the INTAKE getting looser.
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The recommended shim size for EXHAUST is fine, but I have two choices for INTAKE. For INTAKE I have choice of 0.065 (recommended) or 0.051 new clearance. I was thinking I should pick 0.051 with the assumption that they will loosen over time.
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General mech theory states that looser is safer. Am i crazy to go to the tight side? Thoughts?

If I was committed to a shim change because I was out of range and I had a choice of the looser end rather than tighter I think I would go the looser. The theory that the clearance always closes up doesn't ring true for many either.

If I was committed to a shim change because I was out of range and I had a choice of the looser end rather than tighter I think I would go the looser. The theory that the clearance always closes up doesn't ring true for many either.
Based on my trade experience with variety of valve jobs that includes adjustments, I would also choose a thinner shim to have a greater clearance/lash.
The rule of a thumb is: as the valve's face or seat wears, its clearance reduces as well.
Too loose valve is a better and safer option than too tight, which if neglected, will burnt out, resulting in lower compression and misfire that produces HC = unburnt fuel, if ignored, will be plugging up vehicle's cat, not to mention about pollution.

[jimgl3_imp]

let me stir the pot... as valves wear out, clearances tighten. the o n l y thing I can think of that would cause clearances to "loosen" would be weak valve springs. I think it more likely someone just isn't getting an accurate feeler gauge measurement, unless you are really up there in miles or you wring the pi** out of your bike...

that said, carbon build up on the exhaust side can cause a "looser" measurement, but I only mention this because most people post that their exhaust side tightens and their intake side loosens, which the intake side getting looser makes no sense to me whatever.

if mine were getting "looser" I think I would replace valve springs before I started re-shimming.

[GoldOxide_imp]

When rocking in my chair, I will have to describe to children what a camshaft is in their multi-phase induction motor world.

" ... back in the dimming days of the steam engine sonny, some motorcycle companies ... "

[jimgl3_imp]

that's taking the easy way out Goldie! LOL!

Skirting the issue, you might say...

[dave]

spec (IN 0.006, EX 0.011).

The recommended shim size for EXHAUST is fine, but I have two choices for INTAKE. For INTAKE I have choice of 0.065 (recommended) or 0.051 new clearance. I was thinking I should pick 0.051 with the assumption that they will loosen over time.
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I don't understand your numbers. The spec is .006 +/- .001, correct? Where are the values .065 and .051 coming from? Are these the shim thicknesses, or the actual valve clearances, which seems about a factor of 10 off.

Please clarify.

[GoldOxide_imp]

that's taking the easy way out Goldie! LOL!

Skirting the issue, you might say...

Yeah, maybe so. I suppose I have too much faith on Honda reliability under normal riding conditions.

That said, if I suspect the clearances need adjustment, I will put together a plan to address it and just do it.

[bflint]

spec (IN 0.006, EX 0.011).

The recommended shim size for EXHAUST is fine, but I have two choices for INTAKE. For INTAKE I have choice of 0.065 (recommended) or 0.051 new clearance. I was thinking I should pick 0.051 with the assumption that they will loosen over time.
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I don't understand your numbers. The spec is .006 +/- .001, correct? Where are the values .065 and .051 coming from? Are these the shim thicknesses, or the actual valve clearances, which seems about a factor of 10 off.

Please clarify.

Those are the "calculated" new clearances based on the two shim size choices
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New Clear. Calc = Actual valve clearance - (New Shim thickness -Old Shim thickness)
If anybody cares, I copied Mr. LakeWylieJoe's spreadsheets and modified them to do my desktop analysis.
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Contains valve clearance history, new shim calcs, and diagram of final shim changes.

[url=attachment.php?aid=12929]Flint.valves.xlsx (Size: 62.02 KB / Downloads: 15)
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Contains sizes of available replacement shims. I mic'ed the ones I thought applicable to my bike.

[url=attachment.php?aid=12930]Available.Shim.sizes.xlsx (Size: 14.91 KB / Downloads: 2)

[LakeWylieJoe_imp]

I'd go with whichever shim size gets you closest to the center of spec. In other words, when you do the calculation in the manual to select a size, pick the one that is closest to the calculation result. Don't over think it!

[bflint]

I'd go with whichever shim size gets you closest to the center of spec. In other words, when you do the calculation in the manual to select a size, pick the one that is closest to the calculation result. Don't over think it!

[Django]

spec (IN 0.006, EX 0.011).

The recommended shim size for EXHAUST is fine, but I have two choices for INTAKE. For INTAKE I have choice of 0.065 (recommended) or 0.051 new clearance. I was thinking I should pick 0.051 with the assumption that they will loosen over time.
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I don't understand your numbers. The spec is .006 +/- .001, correct? Where are the values .065 and .051 coming from? Are these the shim thicknesses, or the actual valve clearances, which seems about a factor of 10 off.

Please clarify.

For this valve drive type the valves tighten over time, they do not loosen.