Making custom sized valve shims

pCp 252
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Hampden, MA US
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12/8/2016 9:19pm
Has anyone took a 3.00mm valve shim and shaved away 1/100th's of a MM or whatever to create say a 2.975 shim? If so, whats the best way using common tools to evenly shave away some material on the shim? I have a digital caliper to check.


Reason I want to do this is because a 2.95 shim leaves too much clearance, and a 3.00 leaves too little clearance.

On a similar note, which way do the experts err on regarding valve clearance? For example, the KX250F exhaust valve clearance spec is between .17 and .22mm. Should I aim for .17 or .22? Or does it not make a difference?
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Dtat720
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12/9/2016 3:30am Edited Date/Time 12/9/2016 3:31am
It is better to shave the top of the valve stem so the bucket sits lower. Mess with the shim and the cam can gall it and wreak havoc in your top end. Never mess with the shim. If you cant shim it where it needs to be, file off what you need on the valve stem

For clearance, you have .05 range. Go for the middle. .19-.20
neysbo
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Edelstein, IL US
12/9/2016 4:12am
I would think if you have a range of .05 that you can find a shim to work. If you measure 5 shims that are marked 3.00 there will be a little variance and one should be close to what you need like 2.97 or 2.98.
Paw Paw 271
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12/9/2016 4:48am
When shimming valves always go to the larger clearance. This will make sure the valves are 100% sealed.

Paw Paw
BobPA
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12/9/2016 6:21am Edited Date/Time 12/9/2016 6:21am
I ground a few shims back in the early days of four strokes. Shims were $9 a piece and the nice little aftermarket kits were still just a twinkle in Hot Cams's eye. I never had an issue, just a piece of glass, wd40 and some fine grit paper.

A team green mechanic shimmed my bike at Broome Tioga one year. He said if you have a range of say 0.004" to 0.006" that you should be able to fit a 0.004" feeler gauge, but not a 0.006". I've done this for 12 years now with great success

The Shop

mx317
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TN US
12/10/2016 7:55am
BobPA wrote:
I ground a few shims back in the early days of four strokes. Shims were $9 a piece and the nice little aftermarket kits were still...
I ground a few shims back in the early days of four strokes. Shims were $9 a piece and the nice little aftermarket kits were still just a twinkle in Hot Cams's eye. I never had an issue, just a piece of glass, wd40 and some fine grit paper.

A team green mechanic shimmed my bike at Broome Tioga one year. He said if you have a range of say 0.004" to 0.006" that you should be able to fit a 0.004" feeler gauge, but not a 0.006". I've done this for 12 years now with great success
It should be a 0.004 should go and a 0.007 should not if your range is 0.004 to 0.006. I've used this method since the 80s on street and dirt bikes with shims.
mx317
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12/10/2016 8:01am
Dtat720 wrote:
It is better to shave the top of the valve stem so the bucket sits lower. Mess with the shim and the cam can gall it...
It is better to shave the top of the valve stem so the bucket sits lower. Mess with the shim and the cam can gall it and wreak havoc in your top end. Never mess with the shim. If you cant shim it where it needs to be, file off what you need on the valve stem

For clearance, you have .05 range. Go for the middle. .19-.20
Some street bikes have the shims run against the cams, but all the dirt bikes I've shimmed have the shim under the bucket so it would not touch the cams.
Dtat720
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Flowood, MS US
12/10/2016 1:09pm
Dtat720 wrote:
It is better to shave the top of the valve stem so the bucket sits lower. Mess with the shim and the cam can gall it...
It is better to shave the top of the valve stem so the bucket sits lower. Mess with the shim and the cam can gall it and wreak havoc in your top end. Never mess with the shim. If you cant shim it where it needs to be, file off what you need on the valve stem

For clearance, you have .05 range. Go for the middle. .19-.20
mx317 wrote:
Some street bikes have the shims run against the cams, but all the dirt bikes I've shimmed have the shim under the bucket so it would...
Some street bikes have the shims run against the cams, but all the dirt bikes I've shimmed have the shim under the bucket so it would not touch the cams.
Ahh. Under bucket is the better set up anyway. Nice.
CLT809
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Little Elm, TX US
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12/10/2016 5:04pm
I had a piece of plate steel with a threaded hole in it to hold the shim and a bolt to adjust how far it stuck out from the plate. Set that on a wet stone and presto. Never had an issue and you didn't have to compromise on clearance.

In regards to what clearance, aiming for the low side will slightly ease the impact of lobes on buckets and barely effect lift/duration. I was told when I purchased cams from Pro Circuit to set clearances at .004", not .004-.006, just .004. That was on intake and exhaust on both kx250f and crf250.
BobPA
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PA US
12/10/2016 5:30pm
BobPA wrote:
I ground a few shims back in the early days of four strokes. Shims were $9 a piece and the nice little aftermarket kits were still...
I ground a few shims back in the early days of four strokes. Shims were $9 a piece and the nice little aftermarket kits were still just a twinkle in Hot Cams's eye. I never had an issue, just a piece of glass, wd40 and some fine grit paper.

A team green mechanic shimmed my bike at Broome Tioga one year. He said if you have a range of say 0.004" to 0.006" that you should be able to fit a 0.004" feeler gauge, but not a 0.006". I've done this for 12 years now with great success
mx317 wrote:
It should be a 0.004 should go and a 0.007 should not if your range is 0.004 to 0.006. I've used this method since the 80s...
It should be a 0.004 should go and a 0.007 should not if your range is 0.004 to 0.006. I've used this method since the 80s on street and dirt bikes with shims.
Clearly both of our methods work...

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