Scooterotica

I would guess that a single shim the correct thickness is the correct way to do the job.
Bit from a purely engineering point of view is thee a reason two shims can't be used to do the job.

No one?

shimming what though?? specifics man specifics!

Gear box
In this case, but would like to know if there are hard and fast rules.

I think I'd always go for the one shim. Less to go wrong.

One shim for the gearbox main shim. Lots of shops sell shim sets so there's no excuse to not run the correct one. If you absolutely cannot find the right thickness of shim you can have them ground to spec at an automotive machine shop.

It's a pain to set up sometimes but a proper shifting bike is a beautiful thing.

there is a precedent of double shimming, behind the outer bell to assist in chain alignment (Sticky's V1).

Was hoping for an engineer to explain the do's and don'ts.

but thats not the gearbox?

Anyway, gearbox shim as said, one only, never 2. As far as im concerned never 2 on anything as a shim will wear, 2 beside each other will wear each other even more.

I've shimmed a gearbox with 2 shims, it felt like a bit of a botch but it worked. I would think the gearbox oil would lubricate them and not allow any wearing down.

I opened a Nammer once and it had and about 5 shims in, some made from Coke tins

Double or multiple shims might not be absolutely the best engineering solution in theory but in practice would it really make any difference? We are talking about 40 plus year old shopping bikes here not MotoGP

Interesting debate though