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.

 

[SuperGalactian]

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.

Thanks, that confirms what I suspected. In any case, I don’t like not knowing the state of that BB, so a fresh start will give me peace of mind. I will of course do the proper bedding-in process with the new components.

 

[midlife]

The steel of the axle is way harder than the aluminium of the crank so the axle tapers should be OK. However, as it's all off it's just as well to replace the BB for peace of mind.

 

[mickle]

Is the bb cup tight in the shell?

 

[SuperGalactian]

Is the bb cup tight in the shell?

As far as I can tell - I’ve put the cranks back on for now. There’s no discernible play in the axle, however I pull/push/wiggle it. I’ll report back when the replacement parts arrive next week. I need to see the new BB to remind myself which side is LH thread!

 

[C R]

As far as I can tell - I’ve put the cranks back on for now. There’s no discernible play in the axle, however I pull/push/wiggle it. I’ll report back when the replacement parts arrive next week. I need to see the new BB to remind myself which side is LH thread!

Drive side has a reverse thread.

 

[simongt]

Second-hand 1995 Dawes Super Galaxy in decent condition

Bought a 1991 Super Galaxy a few years ago. Very good condidtion for it's age, but first move was to take it into my LBS for a thorough service etc.. No issues with the bike, but if your's had put in a lot of miles, I agree with others that the BB & chainset combination has probably seen a lot of miles and is best replaced.