Shimano UN55

[PRP]

hello,
how many km [or miles] have you got out of a shimano UN55 bracket bearing before replacement was needed? thanks

[RonS]

My Raven has 31,000km and it’s still on the original.

[brummie]

Yeah, the UN55 BB's did last well. I have also been mighty impressed with the long lasting bearings in the FSA headsets Thorn fitted as standard.

[WorldTourer]

Yeah, the UN55 BB's did last well. I have also been mighty impressed with the long lasting bearings in the FSA headsets Thorn fitted as standard.

Curious how headsets became an "install it and forget about it part" (a Chris King headset, or even those's FSA headsets, will probably last, without any maintenance, for longer than the average bicycle-traveler’s travel career), but BBs remain a source of worry. Of course, BBs are more susceptible to road salt, or water ingress during water crossings.

I got about 25,000 km out of the Shimano UN55 on my expedition bike before I ended up switching to different cranks and BB (Shimano XT and Hope, respectively). I then installed the Shimano BB on a bike for local use that probably did about 3,000 km before being sold.

[mickeg]

I almost never hear of a square taper cartridge bearing bottom bracket failing.  And I do not think I know anyone personally that has ever had one fail.

I have spares on the shelf, not because I am fearful of them going bad in the near future, it is more of a fear that I will not be able to find the size I need later if I need one.  Thus, I saw it more as an insurance policy.

I did a group tour in 2012 with a dozen other riders for a week.  One rider had an external bottom bracket fail, the bike was still under warranty, the manufacturer sent a new bottom bracket to a bike shop on our planned route.

I have four friends that have bought Trek Checkpoint bikes, all bought shortly before or during Covid.  Now a second one has had an external bottom bracket bearing fail. 

When I first built up my Nomad Mk II a decade ago, I was nervous about bottom bracket enough that I considered buying the cup and cone parts so that I could clean and re-grease it any time I felt that it was warranted, but now a decade later I am no longer worried about the Shimano cartridge bearing ones.  I have the cup and cone parts with spindle on the shelf, but it probably will never get installed.

[UKTony]

25,000k so far on my Mk2 Nomad. Not in extreme riding conditions.

If you do a search on Ian Wallis on this forum his riding companion, VintageTourer, reports that Ian had done roughly 60,000 km with the UN55 on his Mk2 Nomad before it started to fail and he had to source a replacement (in Indonesia?) before continuing his epic journey.

[PH]

I've had and seen mixed service lives from UN55's and the UN5X's which just have a different cup, a lot of that depends on use and if any additional sealing has been used, but I think there's a fair degree of luck as well. I've had one last less than 10k miles and another 30k, as with all cup and cone bearings it's also surprisingly easy to overtighten, which may have been the case in the shortest lived. I don't think the sealing is great, I know people who've gone to the trouble of fitting grease ports.  I've never done so, but I do offer them a little help by smothering them in marine grease. I do the same with sealed bearing BB's, my oldest IRD one is coming up to the same mileage as my longest lived UN55.
I've had the same experience with headsets, some cheaper cup and cone bearings just let the rain pass straight through, some hardly last a winter before the bearing are sliding rather than rotating. Those with bearings in a cage can be worse than loose or sealed. The FSA that Thorn use are decent, but taking extra measures to keep the water out is worth it, again I just smother them in marine grease, when new and when the forks come out for a service. I've only had one go notchy, the nice thing about sealed bearings is the ease of replacement, having three bikes on the same headsets makes having spare bearings in stock worthwhile (Actually I bought up a couple of headsets when they were on offer for less than the price of bearings!)