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+--- Thread: Valve Adjustment Shims (/showthread.php?tid=14809)
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Valve Adjustment Shims - dave - 06-24-2026
While my question does apply to the CB1100, it also applies generically to most modern motorcycles sold today. I'm posting my question here because I know we have a lot of very talented, and experienced people who frequent this site, and I am hoping someone can provide some informative feedback.
While performing a valve adjustment on a system that uses the small, metallic shims to achieve the proper clearance, has anyone ever encountered shims that have worn to where the surface that contacts the top of the valve stem is concave (cupped), and therefore is not a parallel surface to the opposite side of the shim?
I believe that I just encountered this condition on my VFR800. I performed all my valve clearance measurements, removed and measured all the shim thicknesses, selected the new (thinner) shims required to achieve the proper clearances, and reassembled everything. Upon remeasuring all the new clearances, I discovered the two exhaust valve clearances that I put .003" thinner shims into did not change at all! I double-checked all my measurements before and after reassembly, and triple checked my math. Even if my math was wrong, I know that the replacement shims were .003: thinner than the shims I removed.
I initially blamed myself for just doing something stupid, but when I did a search on the internet concerning this subject I discovered that I am not the only one who has experienced this problem. I learned that my old shims were most-likely cupped where they contact the valve stem, and when I used my caliper to measure the shim thicknesses (the laser-etched markings were not visible), the flat, parallel edges of my caliper could not provide an accurate measurement. I tossed my old shims into a jar, along with the dozens of other shims I have accumulated over the years, so I can't go back and reexamine them now because I don't know which ones they are.
However, I did just order a point micrometer from Ebay, which will accurately measure the shim thickness, even if they are cupped. As soon as I receive my new micrometer I'll finish my valve adjustments (I've only disassembled the rear cylinder at this time).
If anyone can provide some information on this topic it will not only be valuable to me, but I'm sure there are other members who visit this forum who would find this information helpful
Thank you.
RE: Valve Adjustment Shims - rdprdp01 - 06-25-2026
When I read your post, here are the thoughts that I had:
The cupped shims could also be caused by a bad spring or a damaged tappet. I defer to the pros on the Forum. Hopefully, I did not embarrass myself with this post. David
RE: Valve Adjustment Shims - Gone in 60 - 06-26-2026
I got nuthin. If I need a new shim, I order from Amazon (none of the local dealers even know what shims are), check ‘em wirh my Harbor Freight digital micrometer to verify thickness and toss them in. If the final reading is close to what I want I call it good.
I’ve never seen a non-flat shim.
RE: Valve Adjustment Shims - dave - 06-26-2026
(06-26-2026, 10:13 AM)Gone in 60 Wrote: I got nuthin. If I need a new shim, I order from Amazon (none of the local dealers even know what shims are), check ‘em wirh my Harbor Freight digital micrometer to verify thickness and toss them in. If the final reading is close to what I want I call it good.What do you consider "close"? Within the +/- .001 inch tolerance from nominal?
I’ve never seen a non-flat shim.
RE: Valve Adjustment Shims - Gone in 60 - 06-26-2026
(06-26-2026, 06:57 PM)dave Wrote:(06-26-2026, 10:13 AM)Gone in 60 Wrote: I got nuthin. If I need a new shim, I order from Amazon (none of the local dealers even know what shims are), check ‘em wirh my Harbor Freight digital micrometer to verify thickness and toss them in. If the final reading is close to what I want I call it good.What do you consider "close"? Within the +/- .001 inch tolerance from nominal?
I’ve never seen a non-flat shim.
I'd call .001" a tolerable tolerance. I tend to do the math to put my valves on the slightly loose side, so if the variance is to the tight side, I'll still be happy.
That being said, I'm currently monitoring valve clearances on six BMWs, my Enfield 650 and my Bonneville (which I just measured and shimmed within a few thousand miles ago).
My NC750X hasn't gotten to a mileage that needs an inspection yet. I still haven't touched my CB1100, and probably won't.
RE: Valve Adjustment Shims - 1973cb750 - 07-24-2026
shimming can be not fun i always run the bike and let it cool after adjustments made and recheck the clearance before sealing it up always let it cool over night before rechecking also i use after market shims so i always mic the old and the new often when i need .003 i need to use a .004 or .004 to equal the .003 needed nothing is perfect anymore also dirt will take up clearance keep everything sanitary clean like spotless one eyelash will have you chasing your tail most cb1100 require not adjustments even at 100k up to .002 over is ok to tight is a problem even .001 too tight if my spec is like .005 and i see .009 ill leave it be
RE: Valve Adjustment Shims - dave - 07-25-2026
(07-24-2026, 01:15 PM)1973cb750 Wrote: shimming can be not fun i always run the bike and let it cool after adjustments made and recheck the clearance before sealing it up always let it cool over night before rechecking also i use after market shims so i always mic the old and the new often when i need .003 i need to use a .004 or .004 to equal the .003 needed nothing is perfect anymore also dirt will take up clearance keep everything sanitary clean like spotless one eyelash will have you chasing your tail most cb1100 require not adjustments even at 100k up to .002 over is ok to tight is a problem even .001 too tight if my spec is like .005 and i see .009 ill leave it be
"i always run the bike and let it cool after adjustments made and recheck the clearance before sealing it up always let it cool over night before rechecking"
Can you please clarify how you do this? You have to "seal it up" before running it, don't you? Are you saying you put everything back together after making adjustments, run the engine, let it cool, then take it completely back apart again?
RE: Valve Adjustment Shims - 1973cb750 - 07-25-2026
(07-25-2026, 01:32 PM)dave Wrote:(07-24-2026, 01:15 PM)1973cb750 Wrote: shimming can be not fun i always run the bike and let it cool after adjustments made and recheck the clearance before sealing it up always let it cool over night before rechecking also i use after market shims so i always mic the old and the new often when i need .003 i need to use a .004 or .004 to equal the .003 needed nothing is perfect anymore also dirt will take up clearance keep everything sanitary clean like spotless one eyelash will have you chasing your tail most cb1100 require not adjustments even at 100k up to .002 over is ok to tight is a problem even .001 too tight if my spec is like .005 and i see .009 ill leave it be
"i always run the bike and let it cool after adjustments made and recheck the clearance before sealing it up always let it cool over night before rechecking"
Can you please clarify how you do this? You have to "seal it up" before running it, don't you? Are you saying you put everything back together after making adjustments, run the engine, let it cool, then take it completely back apart again?
i take the cover off check clearance ,cams out adjust etc the i just set the valve cover on the head warm the engine up then the next day i recheck if all is good i will reinstall the valve cover and new gasket seal it up always check when stone cold left over night
does not have to be done that way i just dont want bikes coming back so ispend a little extra time to make sure they are good to go
RE: Valve Adjustment Shims - LucienLeFranc - 07-25-2026
Noob question here, quite possibly a dumb one, so apologies in advance:
I seem to remember reading here or somewhere that some experienced folks skip checking CB1100 valves "since they're never out of spec for this precision machine," or something to that effect.
Did I misunderstand that? Or maybe I generalized one member's extreme minority opinion? Do folks truly not hassle with checking the CB1100 valves, or am I on the wrong track and they definitely need checking per the maintenance schedule?
Thanks in advance for helping the new guy.
RE: Valve Adjustment Shims - Cormanus - 07-26-2026
LucienLeFranc, there is no such thing as a stupid question.
Try these threads for further information, https://cb1100forum.net/forum/showthread.php?tid=4317 and https://cb1100forum.net/forum/showthread.php?tid=4095.
I'm no mechanic and I've never attempted to test the valve clearances on the bike by myself, but everything I read here about the experience of many members has led me to the conclusion that it's not such a big deal. There's certainly no need to check them per the service schedule as evidenced by Honda's decision with the 2017 bike to double that interval.
Over the years I've had some adjustments made to mine, but I haven't bothered to have them checked for about 50,000 kms and have noticed no ill effects.
The threads above contain a deal of empirical information about what people found when they checked the clearances.