bottom bracket play - do I really need to change it?

[Nonsteeler]

My bottom bracket has a bit of play. It is clearly noticeable without a chain (maybe 1-2mm) and sometimes while cranking slowly and very defined  (eg  climbing). Apart from that no sensible  problems yet . My questions: What will happens if I don't replace it any time soon? Can I ruin any other parts of my bike? Can it completely breakdown - out of a sudden?

It is a cartridge BB, Ultegra 6500 series (9 speed times). It has done about 25 000km. The BB and the crank (also Ultrega 6500) is now on my fixie cyclo-cross (39x18). So on the one hand it does much less mileage now but it gets its (very) fair share of off-road abuse plus some serious downhill spinning.

[mrcharly-YHT]

The play will cause increased wear in the rest of your drivechain, and I believe can lead to damage to your bottom bracket shell (this is just a personal belief, unbacked by interwebs research).

I say replace as soon as affordable.

[vorsprung]

My bottom bracket has a bit of play. It is clearly noticeable without a chain (maybe 1-2mm) ... Can it completely breakdown - out of a sudden?

I think it will start to make a funny noise and then fail quite quickly
Would I attempt 100 miles with a bottom bracket like you describe? No.  If I did do 100 miles would I get away with it? Probably....

[Nonsteeler]

hmm okay, bottom line (so far) is that I should wait until I hear voices umh noises from down below and then change it ... and if I feel less adventurous change the BB asap, right?

[PhilO]

The play will cause increased wear in the rest of your drivechain, and I believe can lead to damage to your bottom bracket shell (this is just a personal belief, unbacked by interwebs research).

The lateral movement might, I suppose, cause the chain to rub against the cage of the front mech and cause wear there, but I suspect that you'd replace it due to annoyance at the constance noise if that was happening. I can't think of any other way that it could cause drivetrain wear - it certainly won't damage the BB shell. Obviously, if you find that the chainrings are getting close to the chainstays then you should swap it immediately.

There's a theoretical risk that the bearings could fail catastrophically and cause the BB to jam solid, but I've not heard of it happening.

Bottom line: I wouldn't change it until it's materially effecting the ride. I once got another 18 months out of a Shimano Octalink BB on my MTB that had the amount of play you describe.

[mrcharly-YHT]

How can it damage the shell?

Torque, and the angle that it applies to the shell.

This can distort the shell. It's how the frame of my Mercian died.

Replace it asap.

[Nonsteeler]

Thanks PhilO for your reply. This how I more or less  feeling most of the time. As it is a fixed gear bike there is less drivetrain to damage than on a MTB. But then I don't wanna kill the frame for good which is mrcharly's point. I am shivering.  Haven' t though of it yet.

[PhilO]

How can it damage the shell?

Torque, and the angle that it applies to the shell.

Torque from what, about what axis?

Genuinely interested - I'm struggling to visualise a failure mode which could apply the sort of forces that would be needed to damage the frame. 

Ah! Just spotted that this is on a fixie. In that case, the consequances of total seizure would be more serious than my initial response accounted for. That might move me towards a 'replace it' line, but on safety grounds rather than potential for damage.

[mrcharly-YHT]

Torque from pedalling.

The forces are pretty large - most people can exert enough to bend the chainstays.

If the axle is loose in the BB, the direction of the forces changes. The actual amount of torque could be increased depending on the point at which the axle is pivoting.

If the bearings are perfect, then the axle 'pivots' about the centre.

If the right-hand bearing is worn, the pivot point will now move to the left-hand bearing (when pressing down on the right-hand pedal with crank at 3 o'clock).

That's just added about 60mm to the lever arm formed by the pedal, crank and BB axle.

[PhilO]

Hmmm... Not convinced.  If I'm interpreting your description correctly, I can see a theoretical risk, but the number of factors which would have align make it very, very, unlikely in practice.

Still, at 25,000km the BB certainly doesn't owe Nonsteeler anything, so if he has any doubts I wouldn't discourage replacement.

[hubner]

I also don't see how loose bearings could damage the BB shell. It seems to me that as long as the cups are fitting normally, the forces acting on the shell would be the same regardless whether the bearings are loose or not.

I reckon you could keep on using it until the bearings disintegrate.

Also, I don't think it will cause increased wear in the rest of your drivechain either, except for if the chain is rubbing on the front mech. There is some side to side movement of the chain during pedalling anyway. Chainrings, cranks, and frames are not completely rigid.

[Zoidburg]

Swap it out if its on a fixed.

You might unship the chain, which is never good.

[PloddinPedro]

As others have already said, at 25,000k it owes you nothing. If you're prepared to run wornout components such as this, I can't help wondering what condition the chainring, sprocket and chain are in? You've said it moves (laterally I assume) about "1 or 2 mm" If it's really shifting 2mm from side to side (and the cups haven't unscrewed at all) this has to be in the bearings and I think that's a lot of wear. Zoidburg's point is a good one - you can't afford to take chances with a fixed gear transmission; I certainly wouldn't risk it.

What precisely is the reason for delaying fitting a replacement? If it's in a low mileage steed, the next 25,000k are going to take an eternity; over such a timespan, an extra 12 months or so is completely irrelevant.

If it's a budget issue, just fit a cheapie (although personally I don't think the very cheapest are good value for money and it takes just as much time and effort to put in a cheap one as it does a half decent one.)

[Nonsteeler]

Thanks for all your input. I ordered new a BB which was 16 quid (a shimano 105); should arrive any time soon. And yes, it is getting worse (after 25km yesterday) but still no sounds.

What precisely is the reason for delaying fitting a replacement? (...) I can't help wondering what condition the chainring, sprocket and chain are in?

Laziness. Two weeks ago I did my yearly complete service of the drivetrain and noticed the problem. Because I like to ride this bike I put everything together and continued riding it. At same time I just do not fancy to dismantle the whole front drivetrain again (... ok no need to undo the chainring once more) after a couple of weeks. Sure, the reason for servicing was to detect such a problem. But in former times using the 32mm wrench once a year per bike seemed enough. So I was wondering if could postpone replacing the BB a bit. Oh and the rest of the drive train is in a good state, thanks for asking  .

[mrcharly-YHT]

IME, you should never delay.

I had a slightly loose bb. hm, it seems to have worked loose on one side, I'll tighten it. 25miles later. It's working loose again. re-tighten, order replacement.

50miles later. It's really loose now.

Check things. BB is fine. Shell is distorted. After seeking advice (including from Mercian), frame is binned.

Don't delay.

[David Martin]

If the cartridge is fitting into the frame OK then it will not damage the BB shell. Sounds like it is in need of replacement so just sort it as and when. It is  most unlikely to fail catastrophically, but should be changed.

..d

[Nonsteeler]

Okay, just to round it up - the old BB did yesterday its last 22km, the new one is already fitted, so the only question is: What to do with the old BB? Any suggestions for a remotely useful/less post-pedaling life?