Having destroyed the l/h arm of my Middleburns, I blagged an old arm from a mate but the taper on that is borked. It wobbles in all directions, even when properly tightened.

I’m assuming it’s kaput but is there anything I can do to make it usable until I can get a proper replacement?

Any ideas?

I had some success in the past with thin pieces of brass you can get from a model shop as a shim inside of the taper , but you’re fighting a losing battle IMO

That’s what I thought. Might try the brass thing if I can’t get a replacement quickly.

Another trick is a washer which allows you to pull the crank too far onto the axle. Needs to be quite narrow, but works fine. No idea if you can buy them, whenever I’ve needed one I’ve made one on a lathe. A short bit of 15mm (I think) o/d steel tube is pretty much perfect.

I managed a mid wales bodge on some old square tapers with the whatever thin metal we had, mostly it was silver sweet wrappers plus some thin copper squares somebody weirdly had in their rucksack. Rode it twice after that before buying new cranks. I’m pretty sure the sweet wrappers didnt help. But eating the chocolate made it all seem much better. 😉

Coke can shim
Loctite on the bolt
Do it up as tight as you possibly can
Save money and buy new crankset for when it falls off in a few months.

Middleburn square tapers always wobbled loose. The machining internally was never flat, but wavey looking. This used to flatten and the crank came loose. We used to rely on coke can etc to shim out , but as others have said it is only a temporary. I guess that the getting away from square tapers was a good move in crank design. I dont have any of those issues any more myself with cranks just falling loose or off like they used to.

just reading above bodges – you can get copper tape from garden centres to stop slugs climbing in your pots (I shit you not). Maybe you could shim with that, being quite soft, to deform into the right places?

But as PP said – save up for a new one

Ta for all the tips. Garden centre here I come…

correct the taper?

1. clean BB spindle and crank taper
2. thin coat of engineers blue on spindle faces (marker ink at a push)
3. assemble crankto spindle
4. remove crank
5. with a small smooth file, remove high spots (where the blue is) on crank taper

repeat/do above until you get an even coating of blue on the crank taper surfaces after assembly.

then clean up and apply a coating of bearing fit to spindles faces and then assemble – leave to dry for a while before using.

retighten crank bolt after first ride

more time than shims, but you will get a better result and should last longer

I put my worn out square taper/crank combo together with a dollop of chemical metal. It was good for several years. You could even take it apart and re assemble it!

If you speak nicely to Middleburn they can probably sell you a single crank.

Save you forking out for a whole chainset.

They’ve done it for me twice. 😳