Motorcycle Repair: CBX 1000Z Valve Shims, silicon carbide paper, valve shims

Question
Hi again, Jan

Recently bought a 1979 CBX 1000Z and going through all maintenance to ensure everything is A1.

Have come to valve gap adjustment. Measured gaps vary from 0.004 inches to 0.001 inches (0.004 inches is the target I'm using, cold engine). A worrying, slight ticking from the left side of the engine coincides with the tighter gaps on the exhaust valves (might be leakage past valves?)

My question, please - instead of going through the time-consuming and costly procedure of replacing perfectly serviceable (but too thick) valve shims, why shouldn't I 'simply' remove up to 0.003 from the underside of each shim? The exact amount to remove will be dictated by the desired increase in gap (0.004 inches being the target gap). I can do that material removal with a plate glass plate to which silicon carbide paper has been glued, rubbing the shim over the dry (not whetted) paper in figures of eight, frequently turning the shim under my finger(s). Parallelism with the top face can be adjusted by relocating finger pressure. It requires prior practice, but I've done this with clock components, including hardened steel ones, and achieve perfect results. Surface finish can be mirror smooth, using 'Crocus' paper at the end of the process, which is superfine, again stuck to a plate glass plate. That will mean incorrect numbering on the shim, but I regard that as irrelevant - they should always be micrometer measured anyway. A carborundum stone works 'OK, but is slow and difficult to ensure truly flat - carbide paper stuck to glass is superb and surprisingly quick. Thorough cleaning of carbide dust will be essential, but very easy.

My only reservation is that there may be a surface finish (hardening, chrome, whatever) to the shims that must be retained, though I don't envisage any problem provided I only abrade the underside, not the top side that slides against the cam lobe. I'm guessing that the shims are just steel, hardened all the way through. Final, light shim edge chamfering will be necessary, I suspect, to avoid scratching of the follower bore.

Does this seem OK, please, Jan? Can you envisage any problems I've overlooked, please?

With Thanks and Regards
David

Answer
David,  Don't be penny wise and pound foolish.  Shims are only a buck a shim. Most dealers allow you to exchange shims for a buck and your old shim.  Most of us do rely on the numbers on the shims, so if you insist on doing the grinding, remove the numbers.  Also most clubs have a shim exchange program, so you can just replace the shims with the ones you need, this makes the job much easier and MUCH faster.  Especially when you can rely on the numbers on the shims...

The hardening on the shims is likely just a case, so that would be the second reason not to do the job you describe.

Make sure the engine has been run off choke so that there is no carbon buildup anywhere.  I always set the valves a little loose, since tight valves can cause big damage, and these engines can get pretty hot.  So your target of 0.004" is OK.

Good luck,  Jan