Thoughts on bottom brackets?

[graham bowers]

The Deore bottom bracket (SM BB52) on my tourer has a little bit of play. It's done about 7000 Km in all weathers and not always on tarmac.
I'm wondering if an XT BB would have a better sealing arrangement - anybody know please?

 

[Cycleops]

7000km on BB bearings you can replace for about a tenner is not bad going. I’m using the same arrangement and if that’s what I can expect I’m quite happy. You could try some better ones and you might get better service life.
There is more forces when using the outboard bearings of the hollowtech unlike the old square taper UN55 which can go on for intergalactic mileages.

 

[fossyant]

Up to you to see if the difference is worth it. Some things are, like hubs. At least it's not GXP (SRAM), the bearing seals are rubbish. I'll be ordering a new Uber Bike's BB as they have 25% off at the moment and it brings the price down to similar to the SRAM GXP.

 

[graham bowers]

Fair points, thanks. I've probably spent much more on brake blocks in that period so it's not a biggie.

 

[rogerzilla]

The outboard BBs like the shell to be properly faced and can fail quite quickly if they end up non-parallel. If it's done 7000km then it's likely the faces are good enough so you don't have to worry about that. The XT cups cost barely more than the Deore ones, so I "upgraded" when I transferred all the parts from a Hewitt Cheviot to a Surly LHT earlier in the year, The Deore units weren't actually gritty or worn but they'd done a fair mileage and, for a mere £15, I thought the new frame might as well have new cups. I expect the XT ones are a bit lighter, too.

Keep the old LH cup - regardless of the bearing condition, it is useful in the event that you ever want to rebuild a freewheel that's not attached to a bike rear wheel; along with the HT2 spanner, it provides a way to hold the freewheel while you unscrew the (left--threaded) cone.

 

[graham bowers]

The outboard BBs like the shell to be properly faced and can fail quite quickly if they end up non-parallel. If it's done 7000km then it's likely the faces are good enough so you don't have to worry about that. The XT cups cost barely more than the Deore ones, so I "upgraded" when I transferred all the parts from a Hewitt Cheviot to a Surly LHT earlier in the year, The Deore units weren't actually gritty or worn but they'd done a fair mileage and, for a mere £15, I thought the new frame might as well have new cups. I expect the XT ones are a bit lighter, too.

Keep the old LH cup - regardless of the bearing condition, it is useful in the event that you ever want to rebuild a freewheel that's not attached to a bike rear wheel; along with the HT2 spanner, it provides a way to hold the freewheel while you unscrew the (left--threaded) cone.

Thanks. Coincidentally, the bike I'm going to replace the BB on is a Cheviot SE.

 

[Blue Hills]

There is more forces when using the outboard bearings of the hollowtech unlike the old square taper UN55 which can go on for intergalactic mileages.

Yes, which is of course a strong argument for sticking with the UN55. Still miffed that Mr Hewitt fitted an external bearing system to my (very nice) Cheviot SE and I didn't question the spec. Can see myself changing it over at some point, buying a second hand ST Deore chainset to swap new chainrings onto.

 

[Yellow Saddle]

The Deore bottom bracket (SM BB52) on my tourer has a little bit of play. It's done about 7000 Km in all weathers and not always on tarmac.
I'm wondering if an XT BB would have a better sealing arrangement - anybody know please?

No it wont. The bearing and seal on both are identical. There's some cosmetic difference and a number on the price ticket, that's all.

Once you've removed the BB, you'll notice that only the left bearing is worn, the right side will be fine. This is because of a design flaw in the Shimano 24mm hollow axle BB.

SRAM liked the hollow axle concept but couldn't copy Shimano because of a patent. It then went ahead and downgraded the concept by putting a step in the axle where the left crank fits onto it. This step flexes wildly and pushes the bearing out of alignment. Keep in mind that these are deep groove bearings which don't like to have sideways forces put on them. Once the bearing is forced to work, under pressure, when out of alignment, it is a matter of a few hundred kilometers and it is kaput. The seal isn't to blame, it is the weak axle.

Right hand bearings never experience this problem because the axle on that side doesn't transmit torque. Torque is input from the right crank directly into the spider, onto the chainring etc etc. On the left, torque comes from the crank, into the axle (which flexes) and then over to the right hand side, into the spider and out.

Better bearings are not the answer to this problem, only a different axle can improve it. Having said that, an Angular Contact Bearing (ACB) with a 45 degree interface rather than the deep groove arrangement, works wonders. Chris King makes one. It costs the earth.

Edit: Proof that it isn't a compromised seal that causes the bearing to fail is that both sides have the same seals, but only the left fails prematurely.

 

[graham bowers]

Thanks for the detailed reply @Yellow Saddle.
I've ordered a like for like replacement.

 

[SkipdiverJohn]

Yes, which is of course a strong argument for sticking with the UN55.

I'm not interested in any bike bearing technology that doesn't use conventional ball races (caged or loose) and can be stripped down, lubricated, and adjusted externally to take out wear.
I've only recently even had any dealings with cotterless square taper cranks, which I have to say are a practical and sensible design. Up until then, everything I'd owned was fitted with cottered steel cranks.
There is loads of really, really, crap engineering to be found all over modern bikes. Most of it seems to be a "solution" to a problem that didn't even exist in the first place.

 

[Cycleops]

There is loads of really, really, crap engineering to be found all over modern bikes. Most of it seems to be a "solution" to a problem that didn't even exist in the first place.

Di2 being the very best example, but if you want to spend money needlessly then Shimano are very happy to take it off you.

 

[SkipdiverJohn]

For pro racing, I can see the attraction of Di2. But for every other sort of cycling, its completely bonkers overkill.

 

[CXRAndy]

Ive had Di2 for 5 years on 3 bikes. It's such a versatile system, extremely reliable and finger tip actuated. I love my latest upgrade or retro step, by going to triple crankset with Di2. It's made my bike a true all rounder with crisp silent gear changes with trim function to eliminate chain rubbing

 

[Cycleops]

Just like my bike with dreary old cables @CXRAndy .

 

[rogerzilla]

To be fair to cartridge units, the old cup and cone BBs generally fail because of water ingress and rust-pitted races; they are never very well sealed, because they have to be maintainable. If water doesn't get past the perfunctory lip seals on the axle, it comes down the seat tube and ruins the bearings that way. The UN55-type cartridge units have smaller bearings and may not last as long under ideal conditions, but that's irrelevant if you ever ride the bike in the rain.