Stack shims or replace with thicker one?

Motorcycling
#1

Never done this job on an engine like this before, and to save me wasting a ton of money on shims…

When shimming engine valves so they have the correct clearance to the cam, is it possible to stack ones of different thickness to get the correct clearance, or do you replace the existing shim with a thicker one?

To be specific, this is on a 96 Honda CB500V parallel twin engine with DOHC and shims under bucket.

The clearances are super tight and I think they were never checked before by the previous owners of this high mileage bike.

Cheers.

#2

wet and dry, digital vernier :wink:

#3

hmm in answer you need to replace with thicker /thinner …as stacking could mean a shim moves when no pressure exerted and heads into the gubbins below !!!

#4

yup … and a nice strong magnet to hold the shim will make it much easier .

#5

Cheers…I’ll take this option as the job is going to take long enough let alone if were to start filing down existing shims.

In any case the clearances are severely out and I don’t know how thick the current shims under the bucket are until I remove the cams and buckets.

#6

High mileage engine, over tight shims/valve clearances could be an indication of worn valves/valve seats.

I’d be running wet and dry compression tests before taking anything apart just to know how far I’ll need to go before getting started

edit: as above, one correct value shim per bucket regardless of where/how they fit

#7

Oh sorry…I now know what that means re: wet and dry…Thought you were saying to file down existing shims. Doh! :smiley:

Yes I did a compression test before taking the valve cover off, and compression was well within what’s stated in the service manual.

Cheers.

#8

Old experience on shim and bucket engines (but never on a Honda, though it should hold true) si to take things in sensible stages. So:

Note your existing clearances valve by valve.
Work out what “new” shims should be to get the right clearance. (As in +/- whatever)
Strip down to get the shims out and measure them.
See if you can swap a few/couple/one to give you what you need.
Only then go buy the new shims for the rest of the valves. (If you can find a dealer that has what you need in stock!)

These things seem to be silly expensive for what they are so any re-use is worth the very small extra effort.

If all else fails, you can thin them down either on fine emery paper or an oil stone but that is a last resort as they are case hardened and you will be through to the soft core after a few thou.

#9

Nice process.

Think I’ll print that up for future reference.

Cheers.