Brompton bottom bracket woes...(not older BB type)

truman sparks

Active Member
So - I have a 2017 Brompton S6R, which has now had 3 bottom brackets fail, the latest one failing after just one month...

For the past 18 months, I've clocked up around 60 miles per week commuting to work , so bike has maybe covered 4k miles, all weathers, mostly cycle path (tarmac). I'm tall, 90kg and spin, rather than grind...

When replacing BB (which I've done on many other bikes without issue), I don't think I'm overtightening the 'composite' shells, and would have thought that the splines of the fitting tool would make the plastic material give way before doing damage to the bearings (always the drive side failing) - I stand to be corrected though!!

Nearest Brompton dealers are 60 miles away, hence DIY approach.

Any suggestions before I fit number 4?

TIA
 

u_i

Well-Known Member
Location
Michigan
What do you mean by failing? I normally use BBs with replaceable cartridge bearings and on very rare occasions had some rusted or getting deformed bearing balls, but I never had a BB that stopped turning.
 
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truman sparks

Active Member
Thanks for replies - all BBs have been post-recall type and by failing, I mean having excessive play on drive side (so much movement the square taper spindle can be moved 4 - 5mm).

I’ve not been able to trace a 119mm UN55 BB, only 118mm and not sure this will work? Latest failure accompanied by metallic grinding sounds, giving impression that bearing has collapsed...:sad:
 

u_i

Well-Known Member
Location
Michigan
By play do you mean up-down or in-out? If it were in-out, there should be no difference between left and right, but with up-down/front-back your drivetrain should become crooked, so I am baffled.

In my memory there was quite a bit of reserve left in the Brompton's BB-crank combination, at least from the nondrive side ~5mm, but you can exploit the latter with a spacer. I.e. yes, 118mm should work.
 

simon.r

Person
Location
Nottingham
Thanks for replies - all BBs have been post-recall type and by failing, I mean having excessive play on drive side (so much movement the square taper spindle can be moved 4 - 5mm).

I’ve not been able to trace a 119mm UN55 BB, only 118mm and not sure this will work? Latest failure accompanied by metallic grinding sounds, giving impression that bearing has collapsed...:sad:
118mm will work. I have one fitted in my Brompton.
 
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truman sparks

Active Member
Many thanks to all for advice - the play in drive side is vertical rather than lateral/side to side - definitely goosed...

Might also add that u/s BB removal was straightforward and no brute force required, so problem definitely not precipitated by excessive tightening.

Number 4 BB just fitted - Brompton original, but will bear in mind that 118mm will work (without spacer?). Going to send the old BB back to Brompton and see what they say...
 

Kell

Über Member
I have a Shimano UN55 one fitted in mine. Can't remember the width off-hand, but I had no trouble fitting myself, and not had any resulting chain issues.

ETA: just looked back at my order history and I ordered a 68/115.

I can't swear that this one was for the Brompton as I also got one for one of my other bikes, however, in this order was a pair of Brompton Marathon Plus tyres, so I'm going to assume it was.
 
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rogerzilla

Legendary Member
I think I'm using a 113mm but I remember moving spacers in the chain tensioner and hub to keep a straight chainline. I'm using a Sugino XD RH crank, anyway.
 
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