Ok, so I got around to checking the valves today.
I am looking for some input on whether these numbers sound right...
R(ight)-IN(take) was fine,
R-EX was 2.65mm and I calculated a 2.40mm would be correct.
L-IN was 2.68mm and I calc'd a 2.40mm
L-EX was 2.55mm and I calc'd a 2.45mm
Only the R-EX shim bucket was too tight to turn by hand...
Does this sound too drastic? Pulling .2 - .3 mm from each shim seems ridiculous.
Although I think the valves have never been done (1998 with 40,000 km or 25,000 miles)
My method was a follows
a) replace shim with 2.25mm Yamaha shim (29mm diameter)
b) employ feeler gauge until I can just barely detect a slight drag on the feeler.
c) subtract .05mm from the total (2.25mm + feeler gauge from b) to get proper spacing
Someone please let me know if I have done this wrong... before I order the new shims.
And thanks to Kerry for the outstanding video, the mechanical part went perfectly,
CliffHanger
Quote from: CliffHanger on October 31, 2008, 02:35:30 PM
Ok, so I got around to checking the valves today.
I am looking for some input on whether these numbers sound right...
R(ight)-IN(take) was fine,
R-EX was 2.65mm and I calculated a 2.40mm would be correct.
L-IN was 2.68mm and I calc'd a 2.40mm
L-EX was 2.55mm and I calc'd a 2.45mm
Only the R-EX shim bucket was too tight to turn by hand...
Something seems wrong here. Using R-EX as an example:
You made the shim 0.25 mm thinner, which means you've added 0.25 mm clearance... but a 0.25 mm gap is outside the 0.08 mm maximum clearance spec.
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Does this sound too drastic? Pulling .2 - .3 mm from each shim seems ridiculous.
Why? The spec clearances are 0.03 mm - 0.08 mm, so 0.2 mm is a relatively big number.
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Although I think the valves have never been done (1998 with 40,000 km or 25,000 miles)
My method was a follows
a) replace shim with 2.25mm Yamaha shim (29mm diameter)
OK, but you really only need to do this if you don't have a feeler gauge thin enough to measure with the existing shim in place. Also, when you replace a shim you need to turn over the engine to squeeze out all of the oil behind the shim - otherwise, your clearance measurement will be inaccurate (this may be part of the problem from above?)
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b) employ feeler gauge until I can just barely detect a slight drag on the feeler.
OK
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c) subtract .05mm from the total (2.25mm + feeler gauge from b) to get proper spacing
Shim thickness + clearance (i.e. gauge reading) is the total space. You subtracted the desired clearance (0.05 mm) from the total "gap" to calculate the new shim thickness. Makes sense.
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Someone please let me know if I have done this wrong... before I order the new shims.
As described above, I think there is a problem with the new shim thicknesses calculated.
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And thanks to Kerry for the outstanding video, the mechanical part went perfectly,
CliffHanger
That video is fantastic! I'm not sure if you've already seen it, but there is some additional info on the wiki:
http://cgi.stanford.edu/~sanjayd/gs500/Maintenance/CheckValves
Kerry also has a shim selection table on his website:
http://www.bbburma.net/Documents/ValveAdjustmentVideo/GS500_Valve_Shim_Selection_Chart.pdf
To beRto,
I can't seem to figure out how to selectively quote the replies, so here goes...
To clarify, my shim calculating method part a) the 2.25 mm shim is used when the currently installed shim will not allow a .001" feeler into the gap.
Regarding the .2 - .3 mm shim change... this is 4 - 6 shim sizes, which seems like a huge change.
And I am tuning the motor over 3-4 times before checking the gap of the 2.25mm test shim.
Quote from: CliffHanger on October 31, 2008, 03:34:15 PM
To clarify, my shim calculating method part a) the 2.25 mm shim is used when the currently installed shim will not allow a .001" feeler into the gap.
Ah, this makes more sense.
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Regarding the .2 - .3 mm shim change... this is 4 - 6 shim sizes, which seems like a huge change.
OK, I misunderstood you then. I agree that these size changes seem too big.
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And I am tuning the motor over 3-4 times before checking the gap of the 2.25mm test shim.
Hmmm... not sure what the issue could be. It must be a simple miscalculation.
Again, using R-EX as an example:
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R-EX was 2.65mm and I calculated a 2.40mm would be correct.
The worst case scenario would be a gap of zero (i.e. it is impossible to have a negative clearance). So, if we take the 2.65 mm shim thickness and subtract 0.05 mm, the new shim would be 2.60 mm.
If the gap is greater than zero, the new shim would be even thicker. For example, say the gap was 0.1 mm, you would have 2.65 mm + 0.1 mm = 2.75 mm. Subtracting the desired 0.05 mm clearance results in a new shim of 2.70 mm.
I don't see how you could have calculated 2.40 mm?
Ok,
I'll explain the entire process I used for one valve.
R-EX with the 2.65mm that was already there had a gap of 0mm, no clearance; bucket could not be moved by finger.
a) I pulled the 2.65mm and replaced with the 2.25mm to see what the new shim needed would be. (assume 2.25mm + X )
b) To determine X, I used feeler gauges.
A 0.16mm mm feeler felt a slight drag in the gap between the shim and cam. (2.25mm + 0.16mm total gap)
c) The new shim must be 2.41mm (2.25 + 0.16) less the desired gap (0.05). Result = 2.36mm
In this case I'll round to 2.35mm to leave a 0.06mm gap between the shim and cam.
Again, a .3mm drop in size.
I hope this is clearer than my last post,
CliffHanger
Quote from: CliffHanger on October 31, 2008, 04:16:03 PM
Ok,
I'll explain the entire process I used for one valve.
R-EX with the 2.65mm that was already there had a gap of 0mm, no clearance; bucket could not be moved by finger.
a) I pulled the 2.65mm and replaced with the 2.25mm to see what the new shim needed would be. (assume 2.25mm + X )
b) To determine X, I used feeler gauges.
A 0.16mm mm feeler felt a slight drag in the gap between the shim and cam. (2.25mm + 0.16mm total gap)
c) The new shim must be 2.41mm (2.25 + 0.16) less the desired gap (0.05). Result = 2.36mm
In this case I'll round to 2.35mm to leave a 0.06mm gap between the shim and cam.
Again, a .3mm drop in size.
I hope this is clearer than my last post,
CliffHanger
Thanks for the explanation. :)
The original shim was 2.65 mm thick. After your measuring process, you are saying the total space available is 2.41 mm. This is impossible - the total space must be
at least 2.65 mm, otherwise the original shim could never have fit.
I would suggest physically measuring the thickness of the shims (especially the test shim). It could be that it is stamped wrong or worn down.
It is also possible that you are being too conservative with your feeler-gauge measurement. Try going past the point of "slight drag" until you can't physically fit the gauge in the gap. What are the measurements then?
Wait, you said that he couldn't have negative clearance, but if he can't turn the bucket by hand, doesn't that basically mean negative clearance? With 0 clearance, you should still be able to turn the bucket, but if you go tighter than that, you stop being able to turn the bucket, effectively creating negative clearance...
Quote from: beRto on October 31, 2008, 04:31:11 PM
Thanks for the explanation. :)
The original shim was 2.65 mm thick. After your measuring process, you are saying the total space available is 2.41 mm. This is impossible - the total space must be at least 2.65 mm, otherwise the original shim could never have fit.
I would suggest physically measuring the thickness of the shims (especially the test shim). It could be that it is stamped wrong or worn down.
It is also possible that you are being too conservative with your feeler-gauge measurement. Try going past the point of "slight drag" until you can't physically fit the gauge in the gap. What are the measurements then?
The original 2.65mm shim probably set the gap properly. As the valve seat wears down, the gap shrinks.
Is this not the typical behaviour?
My calculation shows that the valve seat has worn down .2 - .3mm
If I misunderstand the process, please enlighten me.
Thanks,
CliffHanger
Yes, that is also my understanding of the process. I didn't know they could be that out of spec with the bike still running though...
Negative clearance is possible, if the shim is bigger than the gap it is holding the valve open by the difference. Your results are possible for the R-Ex but the amount is a bit surprising to me for your milage.
But your new shims for the L-IN and L-EX don't make sense, if you can turn the buckets with your fingertip a .05mm smaller shim would give you proper clearance and a .10mm smaller shim would give you more than the .08mm standard max clearance. Your .1-.28mm smaller calculated shims can't be right if you have zero to a little clearance on these already.
You need to measure the thickness of your shims as suggested.
I had a 97 GS that went 88,000 miles without any intake valve shim changes. The exhaust valves receded into the seats requiring shim changes after about 40k miles, one was down to a minimum 2.15mm shim by 80k miles.
On my 02 GS I changed one intake valve shim once and then changed it back next time so the intakes still have the original shims with over 65k miles on it now. One exhaust valve has had a couple shim changes and the other still has the original. I have slowed exhaust valve recession on the 02 GS by running larger gaps allowing the valves more cooling time on the seats.
http://img.photobucket.com/albums/v443/jcp8832/valveclearances.jpg
Quote from: gsJack on October 31, 2008, 05:46:57 PM
Your results are possible for the R-Ex but the amount is a bit surprising to me for your milage.
But your new shims for the L-IN and L-EX don't make sense, if you can turn the buckets with your fingertip a .05mm smaller shim would give you proper clearance and a .10mm smaller shim would give you more than the .08mm standard max clearance. Your .1-.28mm smaller calculated shims can't be right if you have zero to a little clearance on these already.
You need to measure the thickness of your shims as suggested.
I have measured the feeler gauges and shims and they all match up.
I may not be using the Feeler gauges properly, that may cause me to come up with invalid values.
The feeler gauge should have the slightest friction when inserted into the gap?
Unless I'm just feeling drag from the oil film, I think I'm doing it right.
Would you suggest to drop the shims by 1 step (0.05mm) if they are tight but turnable by hand?
This was the reason I wanted to consult the minds here... I thought the new values were too small for the mileage.
Any other comments/thoughts,
CliffHanger
Quote from: fred on October 31, 2008, 05:25:37 PM
Yes, that is also my understanding of the process. I didn't know they could be that out of spec with the bike still running though...
If the engine has only has one tight valve the engine will start on the other cylinder and the tight valve will loosen quickly as it warms up and the engine will then smooth out and run OK but the tight exhaust valve will burn into the seat much faster.
Valve clearances increase greatly as the engine warms. The aluminum head grows faster than the steel valve as they heat up lifting the cam away from the bucket. I had a CB750 with shim over bucket valves with similar .002-.005" clearances and I pulled the cover and checked them hot once and they were more like .015" gaps hot.
CliffHanger, that's about what I did but I got shims one and two sizes smaller for a valve with a bucket that could be turned by my fingertip but couldn't be measured with a .015" feeler. If the .05mm smaller shim was good I'd probably need the .10mm smaller shim the next time. I soon had a usable supply of shims on hand. :thumb:
A tight exhaust valve will need a .10mm smaller shim and sometimes a bit more. I never used a measuring shim, just checked the gaps and went for shims. I got them from a local dealer, they went up over the years from about $2-3 each to about $13 each for the last ones I got.
The feeler should have a pretty good drag thru the gap but not enough to increase the gap by compressing the springs. If I have a gap that measures .003" by my feel for example I'll try a .002 to make sure it goes thru freely w/o drag and a .004 to make sure it's a no go.
Quote from: CliffHanger on October 31, 2008, 05:58:03 PM
I have measured the feeler gauges and shims and they all match up.
I may not be using the Feeler gauges properly, that may cause me to come up with invalid values.
The feeler gauge should have the slightest friction when inserted into the gap?
Unless I'm just feeling drag from the oil film, I think I'm doing it right.
Would you suggest to drop the shims by 1 step (0.05mm) if they are tight but turnable by hand?
This was the reason I wanted to consult the minds here... I thought the new values were too small for the mileage.
Any other comments/thoughts,
CliffHanger
Sorry, I had neglected to consider that the example shim I used (R-EX) was the one that wouldn't spin. Thanks to gsJack for clearing up the confusion. My response is still valid for the other shims - the "new" shim calculated for those cannot be right for reasons described. Given that those two replacement shims were not calculated correctly, I wouldn't necessarily trust the R-EX measurement either.
Under the circumstances, I think it would still be worthwhile to repeat the measurements until you get results that make sense.
Either way, good luck and kudos for doing your own valve clearance check. :)