BB - External cups to square taper

[jamesbradbury]

On my hybrid, I've currently got a Shimano Deore BB51 Bottom Bracket Cup Set 68-73mm Shell which, predictably, hasn't lasted as long as I'd like. It's starting to click a bit, so I'd like to replace it, ideally with something which will last longer.

I've heard that square taper BBs have a longer life, though obviously I'd need some new cranks suitable for a triple (28/38/48). I'm hoping I can do this getting parts from Spa or Rose for under £50, but maybe I'm missing something.

Looking around, the Shimano UN-55 comes in a variety of sizes (107mm to 122mm), none of which is in the range 68-73mm, so I'm a bit confused. This Stronglight one also comes with English or Italian threading - how can I tell what I have?

Also, presumably I'd need different tools to fit it and some advice on how to get the chainline right?

[pwa]

Ask Spa to supply what you need, including the BB tool (just a socket thing that you use with a spanner). Don't forget to grease the threads well. The Shimano UN BBs just go in until they won't go any further. Spa will supply the right BB for the cranks.

[Gattonero]

It's cheaper to keep the same setup with a better BB, than downgrading to a square-taper BB.

Get an XTR BB, is more expensive but does last a lot longer, it's just better quality.
Make sure the BB shell is properly faced, and all is well greased and lept clean. Do not preload the Lh crank arm too much, the preload cap has to be barely finger-tight. Better to have a tiny amount of axial play, than having the bearings compressed: the latter, shortens their life.

[georgew]

It's cheaper to keep the same setup with a better BB, than downgrading to a square-taper BB.

Get an XTR BB, is more expensive but does last a lot longer, it's just better quality.
Make sure the BB shell is properly faced, and all is well greased and lept clean. Do not preload the Lh crank arm too much, the preload cap has to be barely finger-tight. Better to have a tiny amount of axial play, than having the bearings compressed: the latter, shortens their life.

Having had external BB on my own bikes and serviced many others, I would disagree that changing to square taper is downgrading in any way.
Even with the BB shell faced and the pre-load correct there remains the problem of water ingress with this system which places the BB in the most vulnerable position for this to happen. To swap back to square taper is the first job I do with a new bike as I know from experience that this will save me the trouble of having to replace the external BB sometimes in as short a time as a year.

[TrevA]

Spa recommend a 110mm bottom bracket for their XD2 triple chain set. Depends which chainset you are going for but the Spa website is quite good at telling you which BB you need. I'd recommend the Shimano BB rather than the Stronglight one. My Stronglight only lasted a year and was replaced by a UN55.

[531colin]

Of course moving from external bearings to square taper is downgrading.
External bearings are modern and fashionable.
Also modern and fashionable are the following, in no particular order....
Double chainwheels
"more gears than spokes"
Handlebars down round your ankles
pedaling on tiptoe just so that you can have half a yard of seatpost showing
Anything modern and fashionable is automatically the right and proper thing to do (until, of course, fashion changes)
Anybody who doesn't immediately embrace all thats modern and fashionable is either a dreadful old fuddy-duddy or somebody with a bit of experience and the intelligence to apply their experience, depending on your point of view.

[reohn2]

Of course moving from external bearings to square taper is downgrading.
External bearings are modern and fashionable.
Also modern and fashionable are the following, in no particular order....
Double chainwheels
"more gears than spokes"
Handlebars down round your ankles
pedaling on tiptoe just so that you can have half a yard of seatpost showing
Anything modern and fashionable is automatically the right and proper thing to do (until, of course, fashion changes)
Anybody who doesn't immediately embrace all thats modern and fashionable is either a dreadful old fuddy-duddy or somebody with a bit of experience and the intelligence to apply their experience, depending on your point of view.

That'll be about right.
Spa chainset,good quality and a choice of their own rings,which are also good quality.
Shimano UN55 BB,Spa recommend 110mm,I have 115mm on my two solos and tandem.
Result,bliss.
But as PWA posted make sure you slather the thread in copper grease the BB as it'll be a loooonnnnggggg time before you need to remove it

As Shimano EBB's in a word,garbage.

[bazzo]

I have recently built a bike using a real mix of components.i got the frame which is 531 of a scrap man. It came with campagnolo friction levers, campagnolo brakes and levers and a campagnolo front and rear derailleur. I have fitted new bb and compact chainset, wheels with 7 speed cassette. I have remained the down tube shifters and front mech, rear mech had to go as it wouldn't run the gearing I needed for local hills. It now has a Shimano tiagra long cage rear mech.

My problem is the gears are slipping on the smaller cogs, as all the drive train is new it is obviously not wear, not sure whether I have chain length and tension right. Anyone got any ideas. Is the long cage rear mech too much.

[MikeF]

And yes what's fashionable can be sold at a high price.

On my hybrid, I've currently got a Shimano Deore BB51 Bottom Bracket Cup Set 68-73mm Shell which, predictably, hasn't lasted as long as I'd like. It's starting to click a bit, so I'd like to replace it, ideally with something which will last longer.

I've heard that square taper BBs have a longer life, though obviously I'd need some new cranks suitable for a triple (28/38/48). I'm hoping I can do this getting parts from Spa or Rose for under £50, but maybe I'm missing something.

Looking around, the Shimano UN-55 comes in a variety of sizes (107mm to 122mm), none of which is in the range 68-73mm, so I'm a bit confused. This Stronglight one also comes with English or Italian threading - how can I tell what I have?

Also, presumably I'd need different tools to fit it and some advice on how to get the chainline right?

107-122mm refers to the length of the BB spindle. It needs to be the right length to give the correct chainline and will depend on the crankset. Details on Spa website for example. The 68/73mm measurement is the width of the BB shell on the frame, so that's why the figures are different. I can't comment on the conversion, but BB52 supposedly has better seals than BB51.

[gregoryoftours]

On my hybrid, I've currently got a Shimano Deore BB51 Bottom Bracket Cup Set 68-73mm Shell which, predictably, hasn't lasted as long as I'd like. It's starting to click a bit, so I'd like to replace it, ideally with something which will last longer.

I've heard that square taper BBs have a longer life, though obviously I'd need some new cranks suitable for a triple (28/38/48). I'm hoping I can do this getting parts from Spa or Rose for under £50, but maybe I'm missing something.

Looking around, the Shimano UN-55 comes in a variety of sizes (107mm to 122mm), none of which is in the range 68-73mm, so I'm a bit confused. This Stronglight one also comes with English or Italian threading - how can I tell what I have?

Also, presumably I'd need different tools to fit it and some advice on how to get the chainline right?

I agree with Gattonero about trying a better spec external bb first, but not with his assertion that square taper is a downgrade! I think that would be true only if external bbs lasted as long as a decent st bb. You haven't really got a lot to lose trying a better quality external bb, it would be a cheap experiment- You'd have to buy tools for both types of bb if you swapped over to square taper in addition to a new chainset. The xt bbs are not a whole lot more than deore model, and may well be a lot better sealed.

The deore ones are [inappropriate word removed] - the few I've seen have lasted a matter of months of not particularly hard use. I think that it was Brucey said that part of the reason they didn't last long is because they didn't come with enough grease in them, I dunno about the xt/xtr - maybe there is enough grease in those ones but maybe you could also open it up to check before use. Personally I'm not confident in my ability to do that without damaging the seals, so I'm just running an xt one un-checked. Hardly any use yet so I can't comment on its longevity.

If the bottom bracket shell of you frame is not faced properly it means that the bearings on either side might not be completely parallel - this could contribute to premature bb wear. The external bbs that I've seeen have all died from water ingress though. With an internal bb the bearings on both sides are in one sealed unit so frame prep is not as critical.

If you do decide to go square taper straight anyway you'll need an external bb cup tool which may also come with a preload cap tool to get the external cranks and bb out, a splined bb tool for internal bbs to install the st bb (I'd get a fairly low profile one that enables you to hold the tool in place with a regular crank bolt and a washer) and an 8mm allen key to install the square taper chainset.. Good idea to buy a square taper crank puller too; if you're like me you'll end up pulling the cranks off a few times before you've finished!

You'll need to measure the width of the BB shell on your bike frame and buy either a 68mm or 73mm model of UN55 English thread, the spindle length of which should be matched to your chainset. Your current Deore setup will have a chainline of 50mm.

If you buy a new shimano chainset you are limited to Altus as that's the only square taper left as far as I can see that's halfway decent. The next spec up Alivio is octalink only - definitely not an upgrade. The quality of the Altus chainset is fine in my opinion, although a little heavy. It's also 7/8sp only, although I've run plenty of 8sp chainsets with 9sp setups with no problems. If you wanted you could probably swap your 9sp chainrings onto the new cranks. Looking on the Rose bikes site it is suggested that a 122mm bottom bracket spindle length is required to achieve a chainline of 50mm for this chainset. If you buy one of the Spa cycles touring chainsets you'll have to ask them what bottom bracket spindle length you need to get a 50mm chainline - I think it will differ from what they normally suggest because they're assuming a road bike chainline.

[meic]

My Tiagra external BB started clicking before 3,000 miles, it was irritating but nothing more.
At 4,500 I took off the seals, washed and regreased the bearings with waterproof grease and have now reached 6,000 without the click returning yet.
The FSA that was on before did 7,700 before being removed due to clicking and play, I had left it too late and one side had rusted, so the bearing cartridge was replaced (£2) and top hat seals (£2) and it is ready to go back on when the Tiagra dies.
The Tiagra cost £10.

So it may not be as trouble free as my UNxx's (17,000) have been or my TA Axix light (13,000) but not worth ditching a crankset over.

[reohn2]

Current price for UN55's is £14.49 at CRC,£9.20 at Rose(but there's £7 postage).I bought four @ £7 a pop last time they were on special at CRC
Usually I get 20k out of them.
Yes you've got fork out £35+post for a c/set from Spa,but the overall conversion cost is reaped over time, and you don't have to keep stripping UN55's every pharts end to keep them sweet,just fit(with plenty copper slip on the treads) and repeat every 20K miles .

FWIW,my BB51 went crock at less than 1K,despite me stripping it down when new,popping off the seals and being very careful to fill it with Shimano grease and assemble with correct preload,etc.

No contest IMHO.

[Gattonero]

Of course moving from external bearings to square taper is downgrading.
External bearings are modern and fashionable.
Also modern and fashionable are the following, in no particular order....
Double chainwheels
"more gears than spokes"
Handlebars down round your ankles
pedaling on tiptoe just so that you can have half a yard of seatpost showing
Anything modern and fashionable is automatically the right and proper thing to do (until, of course, fashion changes)
Anybody who doesn't immediately embrace all thats modern and fashionable is either a dreadful old fuddy-duddy or somebody with a bit of experience and the intelligence to apply their experience, depending on your point of view.

"downgrading" is not meant to make a joke out of someone, or to stir an argument. It refers to old technology vs. new one.
FYI I have a few of my bikes running with sq. taper and feel ok.

The point here is, this chap has a new technology crank and wants to put an older one.
No need to write funny things. Just put a better quality BB and keep everything else as it is. It makes a lot more sense than replacing the whole block of parts just because of a single one.

cheers

[alexnharvey]

Rather than downgrading I would consider this change to be using the most appropriate engineering solution for the problem. Where long service life is preferred over weight and performance gain through stiffness, square taper is the long life choice. I do hope the new large threaded T47 solution is better than external and press fit bottom brackets.

If you are fitting a cartridge square taper bb, do yourself or the next owner a favour and use some proper anti seize rather than grease.

[MartinC]

I think Gattonero has a fair point. I would choose ST for most applications but if the OP already has an external BB chainset then the simplest and cheapest solution to try is a better quality external BB. The External v. ST debate is a bit of a red herring.