# Which bottom bracket for this Brompton?



## jay clock (16 Dec 2020)

My neighbour has a Brompton and the bottom bracket has given up. Can someone advise what he needs to replace it with? I think I have the relevant tools, but if it looks like the one in the picture can someone advise what tool










do I need for it?

There only appear to be two different models available on the market depending on the year, so if there is a better quality option that someone can recommend please advise because I was assume these Brompton bottom brackets are poor quality

Thanks for your help!


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## jay clock (16 Dec 2020)

By the way, in case it matters, I think it is a two speed.....


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## rafiki (16 Dec 2020)

Brompton bottom brackets.


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## 12boy (16 Dec 2020)

I replaced mine whith a shimano UN55. I have the bottom bracket tool so its easy to do. Being a philistine I removed the plastic threaded parts of the FAG bottom bracket that came with it with some vise grips. Your LBS should pull the old one and reinstall the new if you buy the new from them. I used a 118 mm. BTW, the one piece Brompton crank spindle is ISO and the newer ones are JIS. Per Sheldon, ISO cranks will work fine on a JIS spindle, and I've found that so.


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## jay clock (16 Dec 2020)

Thanks. He does need a new spindle unless he risks the ISO to JIS situation and Sheldon had too many ifs and buts for our liking. Just a practical question, which way do the different sides of the current BB undo?....


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## Ajax Bay (16 Dec 2020)

I'll take a punt that this chainset needs an ISO square taper. Using a JIS BB is sub-optimal. Get an ISO one. A correct chainline is important.
Differences and compatibility: https://www.sheldonbrown.com/bbtaper.html
Left side normal unscrew. Right side opposite thread.


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## jay clock (16 Dec 2020)

Ajax Bay said:


> I'll take a punt that this chainset needs an ISO square taper. Using a JIS BB is sub-optimal. Get an ISO one. A correct chainline is important.
> Differences and compatibility: https://www.sheldonbrown.com/bbtaper.html
> Left side normal unscrew. Right side opposite thread.


Thanks. Having read Sheldon there are too many ifs and buts so we are going for a new changes it, new chain as that needs replacing and a new bottom bracket with JIS threads. Thanks for the thread advice as well because I can never remember


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## mitchibob (16 Dec 2020)

rafiki said:


> Brompton bottom brackets.



You just had to share the page that also has mods for disc brakes ... I'm going to stop looking.


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## Ajax Bay (16 Dec 2020)

If replacing the chainset is an option then it'd make entire sense to go JIS. The UN-300 has replaced the UN-55 as the lead Shimano square taper BB. Don't know what spindle length the chainset you choose will need but Tweeks have some UN-300s at £15:
https://www.tweekscycles.com/uk/shimano-bb-un300-square-tapered-bottom-bracket-2012876/
and via Amazon @ £14 for a 118 UN-55:

View: https://www.amazon.co.uk/Shimano-BBUN55-Square-Bottom-Brackets/dp/B008YUTWR0?th=1&psc=1


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## Gunk (16 Dec 2020)

jay clock said:


> My neighbour has a Brompton and the bottom bracket has given up. Can someone advise what he needs to replace it with? I think I have the relevant tools, but if it looks like the one in the picture can someone advise what tool
> View attachment 563649
> View attachment 563650
> View attachment 563651
> ...



Shame you're not closer as I have the correct FAG tool to remove it. I know its a retrograde step but personally I would put in an old fashioned BB with loose ball bearings, they run smooth as silk and are much easier to remove, strip and service. The sealed modern BB's are very dubious quality and the Brompton version is crap. However I do have a spare FAG ISO BB which you're welcome to if you want it.


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## berlinonaut (16 Dec 2020)

Instead of wild guessing I would, as often, simply refer to the technical doumentation that Brompton has been publishing over the years. Not too surprisingly it is a reliable source when working on Bromptons. Unfortunately it seems to be less and less publicly available - I typically refer to my archive that I created in better times, when they were easy to get hold of. Don't know why so many people ignore those documents. The datasheet for the task in question is called ds-crankset.pdf and, among other things, it states:


> • In January 2013 a new crankset was introduced with detachable chainrings, this crankset is designed to mount to a JIS taper bottom bracket, it is not compatible with ISO bottom brackets
> • We recommend using the ‘fixed chainring’ crankset (pre 2013) with a 119mm ISO bottom bracket spindle, *if using ISO cranks with a JIS spindle, tighten to 40Nm*
> •Crank bolts and pedals should be tightened to 30Nm and chainring bolts to 10Nm; these must be re-checked after approximately 50 miles of riding


So you can use the old cranks with the new bottom bracket. Which is good news as ISO-bottom brackets in the size necessary for the Brompton (68mm x 119mm) are basically close to impossible get hold of for a couple of years already. In JIS Format there are plenty of bottom brackets to choose from. The original from Brompton is available, ok and reasonably cheap. If you want higher quality or less weight you have to invest more (and have again the choice from various price levels).


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## Ajax Bay (16 Dec 2020)

berlinonaut said:


> simply refer to the technical doumentation that Brompton has been publishing over the years. Not too surprisingly it is a reliable source when working on Bromptons. Unfortunately it seems to be less and less publicly available


Which is presumably why people can't find and refer to them. Thank you for the clue which leads with a search to:
http://www.sjscycles.com/Instructions/Brompton/Brompton_Cartridge_Instructions.pdf
Brompton seems to hide its tech docs behind a 'trade account' wall. Helpful.
Edit: Don't think the chainset which the OP's image shows is a 'spider' with detachable chainrings. So maybe the current BB/chainset is pre-2013 and ISO - a 'wild guess' but, hey, this is Hampshire.


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## Gunk (16 Dec 2020)

If it has detachable chain rings it’s a JIS BB they’re readily available


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## berlinonaut (16 Dec 2020)

The tech docs used to be freely available on the Brompton web page until they massively redesigned it a couple of years ago. From then on there was a subdomain "trade.brompton.com" in the old design, that offered them. This vanished bit by bit but even today there are still some old links working but you have to kow the URL - so old deeplinks from somewhere in the interweb. For a short period of time Brompton offered in the support section of the new website an article that claimed to contain all the tech docs (which was untrue but it contained a reasonable amount). Gone again, relatively recently.
Brilliant bikes used to offer the according techdoc on each article page for a Brompton spare part. Gone since their recent redesing. SJS used to offer some, but not many in the same way as Brilliantbikes - barely none left. 
Today the best bet are older pages of Brompton dealers who know their stuff and some of the country sites as well - some of those offer older catalogues as well. Apart from that some Asian blogs contain some and others can be found on pages like issu.com and alike. It is a total pain in the ass to collect them - took me years but I think my collection is pretty comprehensive. Just that no newly created ones will be added as they do not seem to be published... God knows what Brompton wants to achieve - customer orientation on a technical level has been ripped from their agenda already for years bit by bit and it gets worse every year.


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## berlinonaut (16 Dec 2020)

Here's a tiny data sheet from the trade.brompton.domain about the issue. https://trade.brompton.com/Uploads/QPart/QPart-Datasheets/ds-bbsp_1.pdf
Not totally comprehensive but with the basic information.

Regarding alternative bottom brackets: In JIS style the best bang for the buck is the Token in 118mm with chromo axle. It is more or less in the price range of the spare part from Brompton but of better quality and less weight. There is a lighter version available as well that uses a ti-axle but is more expensive and harder to get hold of. At SJS you can get the various Ti-parts bottom brackets in a range of weights and prices.
If you want a ISO bottom bracket there is still one available from Specialized TA in two different qualities, the TA axis light, both are not cheap. There should be other ISO brackets available but I am not aware of any.


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## Ajax Bay (16 Dec 2020)

Brompton did a recall for BB replacement of 150,000 bikes built between April 2014 and May 2017 with frame numbers: 1403284144 to 1705150001. The OP's friend's bike has the serial number: 1202194675 so probably earlier than 2013.
As far as 'bang for your buck' the 118mm JIS spindled UN-55 from Amazon @ £14 to which I linked ^^^, seems good to me.


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## 12boy (16 Dec 2020)

I would have to respectfully disagree..... I have used cartridge bearings in many of my bikes for tens of thousands of miles and never had any trouble. The tool I use to remove and install them fits on a 2ft breaker bar which works a lot better for me than the hook tool or oval slot wrench needed for the ball bearing ones.


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## berlinonaut (17 Dec 2020)

Ajax Bay said:


> Brompton did a recall for BB replacement of 150,000 bikes built between April 2014 and May 2017 with frame numbers: 1403284144 to 1705150001. The OP's friend's bike has the serial number: 1202194675 so probably earlier than 2013.


Clearly. For one it has a fixed chainwheel - which means the bike was built before April 2013; affected by the recall were only bikes with JIS bottom brackets and spidercrank anyway. Secondly from the serial of the OP's friends bike you can see that it was built in February 2012. So totally unaffected.


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## rogerzilla (17 Dec 2020)

The FAG one often gets a bit stuck and then the metal tool simply chews up the plastic cups. It isn't my favourite design.


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## Gunk (17 Dec 2020)

berlinonaut said:


> Clearly. For one it has a fixed chainwheel - which means the bike was built before April 2013; affected by the recall were only bikes with JIS bottom brackets and spidercrank anyway. Secondly from the serial of the OP's friends bike you can see that it was built in February 2012. So totally unaffected.



If it is a fixed chain wheel then it will need a IOS sealed BB. No longer available from Brompton.


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## berlinonaut (17 Dec 2020)

rogerzilla said:


> The FAG one often gets a bit stuck and then the metal tool simply chews up the plastic cups. It isn't my favourite design.


They have been using a Thun one for a couple of years already, FAG is long gone. Never had a problem with the FAG cups anyway - usage of proper tools and sorrowful handling of it avoids any issues.


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## berlinonaut (17 Dec 2020)

Gunk said:


> If it is a fixed chain wheel then it will need a IOS sealed BB. No longer available from Brompton.


As said before: ISO bottom brackets in Brompton size are close to impossible to get hold of for a couple of years already and Brompton themselves are no exception. But, according to Brompton and again as said before, you can use the JIS bottom bracket with the older fixed cranks despite they were originally used on a ISO bracket. So where is the problem?


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## Ajax Bay (17 Dec 2020)

Problem - just needs care. Measure the current ISO spindle and procure a JIS cartridge BB with a spindle 4mm shorter, if I read Sheldon's advice correctly (I have not needed to do this).
(Sheldon): "If you install an ISO crank on a JIS spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length." The 118mm spindle quoted above is for a Brompton 'spider' chainset with a detachable chainring.
But this discussion maybe nugatory.


jay clock said:


> we are going for a new chainset, new chain as that needs replacing and a new bottom bracket with JIS


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## Gunk (17 Dec 2020)

berlinonaut said:


> As said before: ISO bottom brackets in Brompton size are close to impossible to get hold of for a couple of years already and Brompton themselves are no exception. But, according to Brompton and again as said before, you can use the JIS bottom bracket with the older fixed cranks despite they were originally used on a ISO bracket. So where is the problem?



It’s just at odds at the advice I received from Brilliant Bikes.


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## 12boy (17 Dec 2020)

I've used a JIS 118 BB for years on my Brompton with the one piece, and then when I switched to a 2 chainring 110 BCD set up, put the same one piece on a Xootr Swift with a JIS BB and put another couple 1000 miles on that without a hiccup. That has a 1 x 8 derailleur system and I like the one piece because it is lighter than an aluminum 2 piece and because it had 54 teeth which added a couple of gear inches over the 52 it came with.


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## jay clock (17 Dec 2020)

thanks for all the comments on the obvious levels of deep knowledge on the subject. Problem is solved by ordering a new chain set, a new bottom bracket and a new chain..


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## Tenkaykev (19 Dec 2020)

jay clock said:


> thanks for all the comments on the obvious levels of deep knowledge on the subject. Problem is solved by ordering a new chain set, a new bottom bracket and a new chain..



Missed a trick there @jay clock :
"Problem is solved by ordering a new chain set, a new bottom bracket and a new chain Brompton"


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## jay clock (19 Dec 2020)

The parts Arrived from SJS today, and all fitted. The really difficult but I thought might be removing the old BB, but it was actually fine and the BB shell was immaculate inside.

All fitted and looks fantastic. Thanks to everyone for their advice


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## 12boy (19 Dec 2020)

Shiny and new....looking good, amigo.


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