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does this sound like a I need a new bottom bracket ?

When I turn my cranks with no chain attached, it's pretty smoothe, no real noise and just goes for a while if I let it spin.

When I attach the chain I can turn about half a rotation freely and then it becomes stiff and seems to be in the same place each turn.

I think my bottom bracket is press fit type - it looks like cartridge bearing on either side - I've probably done a couple of thousand miles.

I did just change the cartridge bearings in my rear wheel & hub, think my chain is worn between 75% & 100% from the tool I used to measure.

this may be unrelated but im riding a lot on a turbo trainer - something is causing the chain to vibrate a lot in the lower / harder gears - but appears to be indexed fairly well.

Thanks.

  • Have you checked your chain for suppleness? there may be a stiff link that isn't flexing, effectively tightening the chain at some points. Also, does the BB bind up the same, if you rotate it backward ? – Criggie Aug 24 at 22:57
  • How does the derailleur behave as you turn the cranks? A tight link would show up as it passes the pulleys. – mattnz Aug 24 at 23:43
  • are you experiencing this uneven resistance when it's on the trainer? – Paul H Aug 25 at 0:55
  • Yes, I guess it could be a tight link / chain issue - if i flip the direction of the chain it seems to have less vibrations, I changed the quick link, seems a bit better but not ridden it yet - yes lots more vibration on Turbo trainer (Kickr Snap) when its touching the wheel. – garyconstable Aug 25 at 23:08
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When I turn my cranks with no chain attached, it's pretty smooth, no real noise and just goes for a while if I let it spin.

This does not look like a bad bottom bracket.

When I attach the chain I can turn about half a rotation freely and then it becomes stiff and seems to be in the same place each turn.

However, chain and other attached stuff creates a side load onto the bottom bracket, which may skew the crank axle a bit, and that may reveal looseness in BB's bearings.

Have you tried to wiggle the cranks side to side by hand when they are installed? If you can see or feel noticeable play, then it is a sign of worn bottom bracket.

| improve this answer | |
  • no tbh - it feels pretty solid - its strange everything seems to rotate well on its own, but not when together. – garyconstable Aug 24 at 22:08

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