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Old 06-18-2017, 05:46 PM   #1
Sembalap
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Shim questions

When you choose valve shim, do you go for looser or tighter shim? And why?
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Old 06-19-2017, 06:57 AM   #2
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If I had to, I would go on the loose side. Why? Because Its just safer to go that route, Usually the tolerances get tighter

You can always buy the thicker shim and remove material so you can have it in the middle of the range.

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Old 06-19-2017, 07:34 AM   #3
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+1

The clearance gaps decrease over time so slightly looser would be better than slightly tighter, given that both numbers are within spec.
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Old 06-20-2017, 07:46 PM   #4
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Thanks! So aim for the looser.
But isn't removing the material means you're losing the heat treated surface which will effect shim's durability?
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Old 06-20-2017, 10:28 PM   #5
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Quote:
Originally Posted by Sembalap View Post
Thanks! So aim for the looser.
But isn't removing the material means you're losing the heat treated surface which will effect shim's durability?
Am I reading this correctly?

You don't shave the shim. You replace the shim with one that's a different thickness.
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Old 06-21-2017, 07:33 AM   #6
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Quote:
Originally Posted by Sembalap View Post
Thanks! So aim for the looser.
But isn't removing the material means you're losing the heat treated surface which will effect shim's durability?
What bike are you working on and what are your measurements right now.

I doubt valve shims are heat treated but I'm not 100% sure..... darn! I'm going to have to do some reading now lol.

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Old 06-21-2017, 08:14 PM   #7
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Quote:
Originally Posted by rgbeard View Post
Am I reading this correctly?

You don't shave the shim. You replace the shim with one that's a different thickness.
You are. It's all Pearl's fault lol.

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Old Yesterday, 07:08 AM   #8
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Quote:
Originally Posted by Sembalap View Post
You are. It's all Pearl's fault lol.

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Shims are cheap (a lot cheaper than an engine rebuild). Find the diameter of your shims and order up a hotcams shim kit so you dont have to play to swap game at a dealer.

Also F sanding down shims, that may have worked in the 70's on air cooled engines with looser tolerances but I wouldn't do it.
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Old Yesterday, 08:05 PM   #9
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Wait. I didn't say that shaving down his shims should be his first option. I answered the original question then I implied doing what I've done with a few of my shims.

Sometimes you are stuck in a range that almost put you at the limit an either direction. Shims are usually sold in 0.05mm intervals

Example if your clearance should be between 0.15mm and 0.24mm and your measument is 0.12mm you can either get a clearance of 0.17mm or 0.22mm witch puts you only to .02mm of the limit in either direction. So In this scenario I suggested he goes with shim that will net him the looser setting.

I just bought the thicker shim, took it to a machine shop had them remove .01mm off each side witch gave me a gap of .20mm. That almost puts me right in the middle of the range. I had a few shims modified and from what I have read since this thread started there isn't any special heat treating on the shims. I've had the modified shims in there for 2 track seasons, I check them once a year and I haven't seen any abnormal wear in the shims nor the buckets so in my case it's working out.


Wrote this on my phone, sorry for all the errors.


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Last edited by Pearl zx6; Yesterday at 08:45 PM.
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