# Brompton bottom bracket replacement



## simon.r (25 Jul 2017)

i've just got around to removing and greasing the BB on my few hundred miles old Brompton. It's a FAG with plastic cups - the fixed cup side of which I've sheared off the outer portion:







This doesn't affect the function, but I suspect it will be a hacksaw and hammer job to remove the remains of the cup when the time comes. 

I believe it's a 68 x 119mm JIS taper. 

Any recommendations for a replacement - something with aluminium cups would be nice!


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## simon.r (25 Jul 2017)

Ah, just found this old thread:

https://www.cyclechat.net/threads/w...m-bracket-on-a-new-ish-brompton.207170/page-2

Looks like a good old Shimano UN55 is the answer. Unless anyone knows better?


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## GrumpyGregry (25 Jul 2017)

I was about to post "Ask Adrian"


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## Kell (25 Jul 2017)

I stuck a UN55 in mine. 

Couldn't for the life of me tell you the dimensions off hand though.


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## Kell (25 Jul 2017)

And I've just realised that the link in this thread was to my thread back when I did it...


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## Kell (25 Jul 2017)

And I've just realised that the link in this thread was to my thread back when I did it...


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## Kell (25 Jul 2017)

And I've just realised that the link in this thread was to my thread back when I did it...


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## chriscross1966 (26 Jul 2017)

I favour going through the rather long-winded process to get external cups on, I've got a Shimano Alfine on one of my Bromptons, Campag ultrartorque on two of the others and the new one is getting a Chris King 24 to take an FSA crank...


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## Cadzow (5 Aug 2017)

A UN55 should fit but it needs to be longer than an 118 length BB. A JIS crank on an ISO spindle will go too far onto the spindle so it is best to add on about 4 mm to the spindle length. I've ordered a 122.5 UN55 BB and that should fit okay.


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## simon.r (6 Aug 2017)

Cadzow said:


> A UN55 should fit but it needs to be longer than an 118 length BB. A JIS crank on an ISO spindle will go too far onto the spindle so it is best to add on about 4 mm to the spindle length. I've ordered a 122.5 UN55 BB and that should fit okay.



The 118mm UN55 fits fine, no problem with the standard cranks.


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