IceTee2

I'm looking for a general consensus. I have a '95 Trek 520 that I picked up as a first time winter project. This bike has reportedly less than 500 miles on it (maybe as little as 100 miles). I have gone through the wheel hubs and headset bearings. Little wear and the grease was brown and sticky but not hardened. Right now the bike is stripped to the frame, except the crankset is still in place. I'm considering having the LBS replace the Shimano BB-UL51 with a "55". The cranks spin nicely and there is no play that I can perceive. Since the BB replacement is more than I want to tackle in my garage, there is no 'learning experience' incentive. This bike is going to a friend who is just starting to ride at age 72. Thanks in advance for your thoughts.

Rolla

If the 100-500 mileage estimate is accurate and the bike has been cared for (not stored outdoors or ridden underwater), the BB is probably good to go; those cartridge units are typically good for several thousands of miles. That said, a UN55 costs all of 30 bucks, and takes about ten minutes to install.

Here's an easy test: Install the saddle and seatpost and clamp the bike in a workstand. Put your ear on the saddle and give the cranks a spin. If you hear a nice whooshing sound, it's okay; if you hear grinding or clunking, it's time to replace.

squirtdad

If it is a sealed cartridge BB and is smooth I don't see a need to change it. these should be able to go thousands of miles.

Jeff Neese

A couple of things. First, a new UN55 may not be available. It's not clear whether Shimano stopped making it altogether or if it's just another temporary supply-chain problem, but they're scarce right now. Second, if the bike is as you say and has very few miles on it, why would you replace the UN51? Just have the bike shop disassemble, clean, and repack the bearings. I do agree that it's better to let the shop do that, since they have the right tools and (presumably) experience doing it.

dedhed

UN 51 is a sealed cartridge unit. LBS isn't going to take it apart and will replace with a UN 55 or more likely UN 26 or UN300. Better to just run the existing until it gives trouble

Jeff Neese

The UN51 that's in there now is a better BB than either a UN26 or UN300, and is worth saving if all it needs is to be cleaned and greased. It's an easy job.


If your LBS is unwilling to disassemble your existing BB and will only do a replacement, have them remove it and give it back to you. Clean and regrease it yourself, then take it back to the shop to reinstall it. Or find another shop, someone that knows how to rebuild bearings. What do they do if someone needs wheel bearings repacked, sell them new hubs?

dedhed

Except that video isn't a UN 51. No LBS is going to disassemble a UN 51 cartridge and service it when a $20 UN 26 et al is a 10 minute job. Certainly not cost effectively even if they did. It's kind of the whole point behind cartridge bottom brackets. Note the label "SEALED", maintenance free, R&R when the service life is over. While I agree the 51 is better than a 26 or 300 those will give thousands of miles of trouble free service as would the Tange products.

Jeff Neese

I understand that it's better for the bike shop to sell you a new one. I'm talking about what's better for you, and your bike.

The term "sealed" doesn't mean it's permanently sealed so you can't get it apart. It refers to being sealed against water getting into it while it's on the bike. The bearings in the hubs you repacked may have been "sealed" bearings too. That UN51 can be disassembled and cleaned, and you'll end up with a better BB than a UN26. If it were me and I didn't have another shop nearby, I'd pay the LBS to remove it, and then reinstall it when I brought it back to them the next day all cleaned and greased up, just like new.

If you don't feel like messing with it and just want them to put in a new one, the Tange may be a better choice than the newer Shimano UN26 or 300. But if it really has low miles, definitely save the UN51. Someone here may offer you a few bucks for it, maybe me. What's the spindle length?

HillRider

Even if the LBS knows how to disassemble, re-grease and reassemble that UNB51, the cost in time and labor would be prohibitive compared to replacing it. If, as you say, it sounds good and has no play, just have your friend ride it and stop worrying. As noted, these things last many thousands of miles and, when and if it wears out, you will get plenty of warning. As a couple of posters here are fond of saying; "never fix a running part".

mprince

It sounds like you are trying to push what you feel is better for you, and your bike. A shop (if you can find one willing to do it) will charge more to rebuild the cartridge BB than the part is worth. Not sure how that makes a lot of sense, in reality those are not designed to be serviceable, and it's not like the BB is super rare/unobtainable or high-end as it is. Current supply chain challenges aside, just doesn't add up when there are multiple replacement options which are quite affordable.

A colleague of mine has a nice saying - "Just because something could be done, doesn't mean it should be done"

Andrew R Stewart 

In my years of working with the Shimano tapered square cartridge BB units I know of none that were cleaned and regreased by a shop or the rider. Zero. Not that it is impossible, just as others have said not cost effective. Shimano has made no design or assembly provisions for rebuilding these units. Brfore I would begin to try to do this I would want a good replacement on hand, just in case I were to find out why this is not something done Andy

Jeff Neese

When you say they're not meant to be serviceable, that's true with regard to replacing bearings or refacing surfaces if things are worn, but they are easily disassembled and repacked with fresh grease, if that's all it needs. It's not super high-end, but it's a lot better than the current offerings by Shimano. Yes, to pay a bike shop to do the rebuild may not be cost-effective (depending on their hourly rate), but the OP has already repacked his headset and hubs, so if he can do that, all he would need to do is pay the shop to remove and reinstall. That should be cheaper, and he'd end up with a better bottom bracket. Why would you toss a perfectly good UN51? If you found one NOS but the grease was hardened and stiff, would you just throw it out?

It's really a shame. All of my bikes are square taper and most of them have UN55s. The current crop of Shimano are a downgrade, so my next one will probably need to be Phil Wood or at least Velo Orange or Tange.

ThermionicScott 

One could consider them a "downgrade" from Shimano's old construction, but it really just seems to bring them down to the same level as most other cartridge BBs that use two cartridge bearings, pressed onto a spindle, separated by a cylindrical spacer (Tange, Velo-Orange, IRD, etc). The UN300 I bought recently out of curiosity seems well-made, if nothing else. I think it all comes down to the bearing quality and sealing, really.

Jeff Neese

That was my conventional wisdom too, until recently. You'd just throw a new UN55 in there and for the price, that was the way to go. But now they're not available, and bottom brackets of the same quality are more expensive. That changes the equation.

I'm not advocating for rebuilding the UN51 just because he can. I'm really trying to discourage downgrading to a UN26 or UN300 just because it's easier, when he has what sounds like a perfectly good UN51 that just needs to be cleaned and refreshed. To get something at least as good, he's going to have to spend more money than a UN26 costs.

And let's not forget that he's talking about a '95 Trek 520. It deserves better than a UN26. If it was mine it would probably get a Phil Wood bottom bracket.

70sSanO

I believe the consensus is to let your 72 year old friend ride the bike with the UN-51.

If there is a perceived need that a replacement will be necessary for your friend, buy a UN-55 as a backup if you can find one.

Removing a square taper crank, just for the sake of it, is worse than potentially having to replace the BB down the road.

John

John Valuk

If the BB is smooth and nice, then you don't need to do anything.

If and when the time comes to replace the BB, then one could put in a UN-55 (if they can find one; now discontinued), or a Shimano UN-300, or an Interloc Racing Design QB-55, or any of a bunch of other options.

jasoninohio

If the bike has low mileage and no signs of wear then the bottom bracket probably doesn't need any attention, I think that's the consensus right?

Re: servicing cartridge bearings, I did find it funny that the external bottom bracket in the video linked above says "Do Not Disassemble" right on it... The square taper cartridge BB uses standard cartridge bearings like from a skateboard wheel; sure you can pry the seal out and mess with the actual bearings, and maybe you get it put back together right, but isn't the whole point of cartridge bearings to eliminate needing to re-pack them? And in the case of the bottom bracket, it's cheaper to just replace the whole assembly instead of pressing new bearings on to your existing spindle (plus the tapers could be worn).

For the best of both worlds just retrofit it to a cup and cone BB and grease it as much as he wants haha

Andrew R Stewart 

Philosophically I agree with not downgrading and being able to service what you already have. I grew up in the LBS world when one could get der cage plates, various springs and screws and other sub assembly bits (remember the Campy cabinet?) We rebuilt many IGH hubs, ders, brake calipers besides the usual bearing servicing back then and we offered three brands of freewheels with custom cog sizes. But, you know, the industry has moved on from that business model. For better or worse.

One aspect of this shifting of the service/business model is that manufacturers don't need to make their products user serviceable. Again for better or worse. This means that they can assemble products with designs that are not meant to be taken apart and reassembled and don't offer the support bits (not meaning the bearings but the plastic seals, clips and retaining rings) that can become damaged on disassembly. So sure, one might be able to unpress fit the innards and find that the reassembly needs other then just bearings to work again reliably. Andy (who runs some Shimano UN units and some Phil ones on his bikes)

John Valuk

Some bottom brackets that were referred to as "cartridge" units were constructed in ways that did not use standard "bearing cartridge" assemblies.

Today, yes, we mostly see designs that are based on standard bearing cartridges.