This may be a dumb question about valve shims but.....

[mmatches1]

I had a mechanic show me how to change valve shims and he told me that the more the valves wear the smaller the shim size. The manual seems to say that as the valves wear you use larger shims. Can anyone clarify this? I am also trying to figure out how advanced my valve wear is to determine how much life there is in this bike before a valve job. The valve shims were larger numbers like 2.90, 3.10, 2.85 etc. The mileage on the bike is 27,000 and I am worried that the bike may have 127,000. Any help would be greatly appreciated.

[tcoop]

As the valves get used they tend to wear into the valve seat, which closes the gap between the shim and the cam. So the valve shims will get smaller as time goes on.

[BA80]

There is very little wear on the upper portion of the valve train. (cams & shims ) These engines wear mostly on the vave seat itself as they slam shut.

As it wears the valve clearance will become less and less so a thinner shim is usually what is needed to correct the clearances. When you reshim the valves, shim to the wider side of the spec and it will wear in.

There is a chart to figure what shim thickness you'll need in the tech tips at the bottom here.

[LoHo]

Having thick shims now, while maintaining proper clearance, is a sign of valve seat health and lack of wear.

[DGXSER]

Yep, the valves wear into the seat, letting the valve stem get closer to the cam, and so the bucket closer to the cam. So gap closes as valve seat wears. What you have are some pretty thick shims. Must be close to factory installed shims.

I highly doubt 127,000 miles on the engine or the bike. For one thing, those shims are very thick and it would have to have had shim adjustment in 127,000 miles. Additionally, it is not common for these bikes to have seen that amount of use. Alot of them develop the second gear issue, or some form of carb performance problem and get sidelined.....for decades in some cases. So that 27,000 mile number is perfectly feasible, and more likely than the 127,000.

[mmatches1]

Great information and exactly what I needed - thank you.

[MaximPhil]

Great information and exactly what I needed - thank you.

If those 27,000 miles or kilometers were carefully ridden and you shift positively ( firmly not violently) you may never have the dreaded 2nd gear issue
Phil

[mmatches1]

I checked the manual again and the calculation they use is incorrect - odd. They add the recommended clearance to the existing clearance and add the total to the existing shim size resulting in a larger shim. I found a handy shim calculation charts on this site (not sure if thy are on our site).

http://www.xs1100.co.uk/

[DGXSER]

Those are the same charts in the FSM and other locations.

The way the chart works is to first measure your current clearance. Say your gap has closed up over time and instead of the stock gap for 78-79 intake valves of .16-.20, you now have .06. Look down the left hand column to the second row that is for .06-.10 gap. Now look across the top of the chart for the existing shim size, say it is a 295. Now find where the 295 column and the .06-.10 row intersect and you will see the new shim size should be a 285, or smaller shim. Note that the exhaust gap is .21-.24 for all years, the intake gap dropped to .11-.15 for the 80-82 engines. There is another chart for those sizes, or you can simply adjust the gaps shown in the left hand column down one row so now .11-.15 aligns with the blank row.

HTH

[crazy steve]

That chart is a PITA....

I've found that it's much easier to check the valves using inch measurements. You're looking for .006-.008" on the intakes (early spec), and .008-.010" on the exhaust (all). Each incremental change in shim size (either larger or smaller) equals .002" change. So if you have .004" clearance and want .008", the difference is .004" or two sizes thinner. If you have a 280 shim, swap to a 270.

IMHO it's better to adjust to the 'big' side of the recommended clearance as the clearance will get smaller as things wear, so that will give you more time between adjustments.

[bikerphil]

Steve, it seems you and I are the only ones who prefer the English measurement system with these shims. It is soooo much easier that way, JMHO

[crazy steve]

You can lead a horse to water....

I don't even own a set of metric feeler gauges, and can't see any reason to get any...

[DGXSER]

My new fangled feeler gages have both english and metric on each one. They are in .001" steps, and each has the equivalent metric on it.

When you have teenage kids around you end up buying tools more often than once every quarter of a century.

[mmatches1]

Where did you get that feeler gauge? I purchased the K-D Delux model and it has 32 blades.

[BA80]

Each .001in is .0255mm. Shims are in .050mm increments so each .002in is one shim size.