Firstly, yes I rode too far with loose cranks. Yes the tapers are damaged. Yes I threadlock the bolt when I have some to hand. No, it still comes loose eventually…

Middleburn RS8 square taper cranks on Shimano UN?? BB keep coming loose on driveside. Upon tightening cranks up yesterday mid ride, they have drawn too far up the spindle and are now just interfering with the BB end (not frame). BB had to be as narrow as possible to help chainline issues, and it was always super close – I’m guessing fractions of a mm here.

Any ideas on how to ‘pad’ out the crank to increase the clearance? I recall some ‘pro-tip’ mentioned in a LBS way back: grease mixed with talc, that set hard under pressure. Idea was to fill any tiny gaps between crank taper and spindle. Anybody tried similar?

Other option is to file down the outer edge of the BB cup or the inner edge of the Middleburn lock nut, but I’d rather get the crank sitting further out. Final option is to fit a longer BB, but then I’d have chainline issues again.

Your cranks are ****ed, sorry.

Either keep trying to sort them, spending hours and messing up every ride, or bin and replace.

Are you running triple? singlespeed?

Could it be possible to get a longer BB, the flip the chainring round or space it out to get to your chainline, or play with anything hub end?

But by the time you’ve spent the money sorting it you might as well just get a new arm off the bay or similar.

As above, they’re dead

Try a bb with slightly longer spindle …
I had similar issues on my Karate Monkey with the same cranks running ss ..2.5mm didn’t make a huge difference to chain line

Edit – Thanks for the comments.

Singlespeed_Shep – Member
Are you running triple? singlespeed?

SS with a non dished Homebrewed ‘uno’ ring, so no options for flipping and reversing.

Try a bb with slightly longer spindle …

Longer BB will give chainline issues. As it is, it’s only ok with the cranks right next to BB. 73mm BB shell… 🙁 (I could get 5 mm taken off the frame… :-/ )

Can’t face writing them off for a few thou. clearance.

cynic-al – Member
Either keep trying to sort them, spending hours and messing up every ride,

I take your point, but they don’t come loose every ride. ~One in five, which these days, would be about annually…

Grind/file the inside face of the crank arm down just enough to clear the bb cup.

Hmmm. Maybe I should have done a search 😳

http://singletrackworld.com/forum/topic/can-i-shim-a-square-taper-crank-arm-on-to-a-axlepic

are you using a normal free wheel at the back with ss spacer kit

Bit of coke can as a shim may save it but if there is any rotational play, you are stuffed ime.

singlecrack – Member
are you using a normal free wheel at the back with ss spacer kit

Afraid not. White Industries ENO screw on.

mattbee – Member
Bit of coke can as a shim may save it but if there is any rotational play, you are stuffed ime.

As far as I have noticed, there’s not been any rotational play, just sideways. I’ve pulled it apart and added some shims, and it’s all turning freely again, but it’s too wet to go for a pedal to see if it will hold. (If they are ruined, might as well try…)