RH crank movement on square taper BB - what to do?

[SuperGalactian]

Second-hand 1995 Dawes Super Galaxy in decent condition, 8sp Shimano LX on square taper BB. Exploring a creak apparently from bottom bracket (yes, I know, could be anywhere on the bike), I discovered definite slight movement in the rh crank when I put weight on rh pedal (bike stationary). Moved once only, easily felt underfoot and also visible, but no noise that I could hear. Couldn't be repeated until I applied weight to lh pedal, which showed no corresponding movement. Alternating sides like this recreated movement of rh crank every time, but still the movement was felt only on the rhs.

I suspected a bad interface between the BB taper and the corresponding hole in the rh crank, though that wouldn't explain why I had to kind of re-set it using the lh crank before it would move again.

Anyway, I removed both cranks, cleaned the tapered ends of the BB, examined and cleaned the holes in the cranks. The latter were not worn shiny all the way through the crank, but the wear pattern was not noticeably uneven. I could detect no play in the BB, which turns silently and smoothly. I put a smear of anti-seize on the tapers , re-fitted the cranks, and torqued to 30Nm.

But ... the rh rank still moves slightly under weight as described above.

I was in any case considering swapping out the chainset, chain and cassette for 9sp. Should I get a new BB at the same time?

 

[fritz katzenjammer]

If you have cleaned the components and reassembled them to the correct torque and you still have play I would replace both the bottom bracket and the crank arm. Once they worked on each other for any length of time the mating surfaces are likely both toast, I wouldn’t take the chance.