Drive side crank coming loose

[Gattopardo]

The drive side crank on the bromptom has come loose after being tightened. 

So am suspecting the the crank or bottom bracket is buggered but can't see if there is any damage.

What to do?  Shall I clean the bb square taper surfaces, and the crank mating surface.  The clean the thread and bolt then torque up.

[Jurek]

I can do you a very low mileage FOC BB and chainset from my little-used 2013 Brommie, if you can get yourself over to Forest Hill.

[Brucey]

most likely that the crank (being soft aluminium) is wrecked rather than the BB spindle (which is hard steel).

cheers

[rogerzilla]

Agreed.  It's due to it coming slightly loose and then there being enough movement for it to trash itself.  Tighten crankbolts again after the first 100 miles on a new crank, then remove them, clean the threads and put them back in with threadlock.  Never touch them again until the BB wears out.

Aluminium crankbolts fitted at the threadlock stage are a good disincentive to retightening.