06-24-2026, 01:16 PM
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.
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.
