# What do I need to change a Bottom bracket on a new(ish) Brompton?



## Kell (14 Sep 2016)

I've not looked at this properly yet, but got a clunking noise on my Brompton last night. When I picked it up to have a look, the whole crankset is moving.

It may be that it just needs tightening, but essentially, I'll need the same tools for that as for removal. The question is, is the current Brompton with a Spider chainring just a simple matter of crank pullers and a Shimano BB tool? Or do I need something special?

Thanks in advance.


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## Kell (14 Sep 2016)

Also - if I do decide to replace it, what are people doing in terms of upgrading?


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## Fab Foodie (14 Sep 2016)

Kell said:


> I've not looked at this properly yet, but got a clunking noise on my Brompton last night. When I picked it up to have a look th ewhole crankset is moving.
> 
> It may be that it just needs tightening, but essentially, I'll need the same tools for that as for removal. The question is, is the current Brompton with a Spider chainring just a simple matter of crank pullers and a Shimano BB tool? Or do I need something special?
> 
> Thanks in advance.


Crank pullers and Shimano square taper BB removal tool.

I upgraded to a 50/34 Stronglight double on the same BB. Gives me 2 gear ranges. Even with the 34 you get a useful gear range over flat ground. £50 well spent for me,


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## Kell (14 Sep 2016)

Thanks for that. 

Looks like there's a Shimano UN55 in 68x118. The details on a direct replacement says it's 68x119.

Would that cause me problems? Clearly the chain line is going to slightly further in, but is it enough to make a difference?


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## Tim Hall (14 Sep 2016)

Kell said:


> Thanks for that.
> 
> Looks like there's a Shimano UN55 in 68x118. The details on a direct replacement says it's 68x119.
> 
> Would that cause me problems? Clearly the chain line is going to slightly further in, but is it enough to make a difference?


That's 0.5mm per side. I'd say you'll be fine.


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## mickle (14 Sep 2016)

New?

Warranty!


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## Kell (14 Sep 2016)

It's just over a year old. 

And done about 2,500 miles.

Might not actually need replacing, could just be that it's come a bit loose, but I figure an upgrade would be no bad thing.


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## GrumpyGregry (14 Sep 2016)

Kell said:


> It's just over a year old.
> 
> And done about 2,500 miles.
> 
> Might not actually need replacing, could just be that it's come a bit loose, but I figure an upgrade would be no bad thing.


If it is so loose the cranks are wobbling either your bb or your cranks, or possibly both, are now likely scrap.


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## Tim Hall (14 Sep 2016)

mickle said:


> New?
> 
> Warranty!


Wot Mickle says. Mind you, a few years ago we had what felt like a loose/worn bottom bracket on The Boy's bike, after one year use. Took it back to Evans, who said bottom brackets were consumable and it wasn't a warranty item. I <polite version> expressed incredulity but they wouldn't budge. Closer inspection at home revealed that the adjustable cup had come loose, easily remedied by application of BB tool, 32mm socket and suitable amounts of grunt.


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## Tim Hall (14 Sep 2016)

GrumpyGregry said:


> If it is so loose the cranks are wobbling either your bb or your cranks, or possibly both, are now likely scrap.


The BB could be shot while the cranks remain true on the square taper, so not damaging them.


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## shouldbeinbed (14 Sep 2016)

Have you got the old style FAG BB with the castellated plastic lockring?

If so, you'll need the relevant spanner, Park Tools BB4 IIRC or a bodge to get it off. I didn't have one so nipped into LBS and borrowed theirs.


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## Kell (14 Sep 2016)

I thought it might need a specific tool as it does have crenellations on the outer rings, but it also has splines which look like they'd take a Shimano bb tool.

And yes, I'm aware it's minging.


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## 12boy (14 Sep 2016)

I can't tell from the photos I pulled up if the UN55 has a plastic ring on the left. If it does I would recommend not tightening it to much, i.e. flush with the frame. I have had a number of those split from overtightening. All it really does is support the bracket on that side and tightening, or not, does not affect the cartridge bearings. If it is aluminum it won't split and you can tighten further. It is the right side that really matters. BTW, I grease the threads before installing, so as to prevent rust and sticking when later you replace it. I do not grease the square taper ends of the spindle. Remember that the right side ain't "lefty loosey, righty tighty" since the threads are reversed on the right. I replaced the original FAG bracket on mine with a Vuelta 119 mm, about 12 bucks, and it works fine thousands of miles later.


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## GrumpyGregry (14 Sep 2016)

Tim Hall said:


> Wot Mickle says. Mind you, a few years ago we had what felt like a loose/worn bottom bracket on The Boy's bike, after one year use. Took it back to Evans, who said bottom brackets were consumable and it wasn't a warranty item. I <polite version> expressed incredulity but they wouldn't budge. Closer inspection at home revealed that the adjustable cup had come loose, easily remedied by application of BB tool, 32mm socket and suitable amounts of grunt.


Not just Evans that say that


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## Kell (14 Sep 2016)

I just put a un55 in my road bike at the weekend and that had aluminium rather than plastic.


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## mickle (14 Sep 2016)

Kell said:


> I thought it might need a specific tool as it does have crenellations on the outer rings, but it also has splines which look like they'd take a Shimano bb tool.
> 
> And yes, I'm aware it's minging.
> 
> View attachment 143925



I could have sworn that you said it was new.


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## shouldbeinbed (14 Sep 2016)

Kell said:


> I thought it might need a specific tool as it does have crenellations on the outer rings, but it also has splines which look like they'd take a Shimano bb tool.
> 
> And yes, I'm aware it's minging.
> 
> View attachment 143925



Thats the FAG type I alluded to. Park Tools BB4 (tho check to be sure)

You're best off nipping into LBS and asking to use theirs as Brompton have moved away from that to standard Shimano tool style and upgrade BBs will not be of the FAG type either.


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## Pat "5mph" (14 Sep 2016)

User said:


> Use a pipe wrench, carefully.


I did this, with the aid of an old t-shirt as a buffer to avoid damaging the ring.
Not on a Brompton though, just some old bike I was dismantling.


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## Kell (15 Sep 2016)

My Shimano BB tool fitted perfectly. 

(one of these type)







They're only nylon cups, but the drive side was loose. Nipped it up a bit, but have also ordered a new Shimano one.

The UN55 seems to be pretty much bullet proof, so I think it's worth doing.


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## Kell (15 Sep 2016)

mickle said:


> I could have sworn that you said it was new.



I meant new as in 'the new style' with the spider chainring as opposed to the old one piece version.

Anyway, tightening it up has cured the clunk, but I'm still going to fit the new BB. For the sake of £15, it's worth doing.


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