Help with old brompton BB

[cimh]

Hello, first post here. My 30+ yrs old 3 speed brompton Is having a new lease of life with my Swytch kit. But it could do with some love. I would like to replace the worn crankset, sprocket and chain which is within my ability. But I am not sure about the BB. It sounds dry and has some slack but it spins and works and the bike is only used recreationally. It looks relatively easy to install a new JIS cartridge which would open up crankset options but looking at the existing bb I have a nasty feeling that it will be a pain to remove given its age.

Unfortunately as this is my first post It doesnt look like I can post photos of the BB but here is a link to them (apologies if this does not work either)
https://photos.app.goo.gl/XdAk3j15YWG6Na8u6.

The BB looks old with metal endstops each end - The chain side stop has an 8 sided nut shape the other side has 4 notches at 90 degrees to each other and a 24 ish mm hex further inboard. Being a keen diyer I dont like to admit defeat but I wonder what people think. I'd be interested in knowing its make / type and should I just use it (if it aint broke dont fix it)? Could it be oiled? Is it likely that it could be removed by a diyer with the right tools or is it a shop job.

I would much appreciate any advice. Thank you

Apols if the images do not show.

Cimh

 

[Chris S]

That's a square-taper cup and cone bottom bracket. You should be able to remove the adjustable cup (the one with a lockring on) fairly easily. You will then be able to slide out the spindle and grease or replace the bearings inside.

The fixed cup will probably be rusted in place which would make replacing the whole unit more problematic. They can be removed but you will probably need lots of a WD40 and a long extension bar on your spanner.

PS The fixed cup will have a left-hand thread. You will need to turn it clockwise to undo it. The other cup unscrews as normal.

 

[cimh]

Chris S - Thank you so much for that advice. If you have suggestions on what tool might be best for the lockring that would be great. The fixed cup looks like it would need a 36mm spanner but perhaps these old brackets were made in imperial units?

Sounds like its safest to try open up and check / grease the current bb than totally swap it out.

Finally (I hope), if I did manage to remove the bb completely would the threads in the frame still be compatible with the standard JIS bb sold for bromptons?

 

[Chris S]

You're supposed to use a lockring spanner but I just use an old screwdriver and a hammer. Give it a squirt of WD40 first.

Once you've got the spindle out you can accurately measure the distance across the flats of the fixed cup. I doubt if you will find a spanner that big, you will probably have to use a pipe wrench to remove it. I'd leave it in unless it's so badly worn that it's causing the spindle to wobble.

I don't have any specific knowledge of Bromptons but ISO and JIS bottom brackets both use the standard 26 threads per inch. The ISO spindle is slightly longer. You can still mix ISO and JIS spindles and cranks but the crank arms will sit 4.5mm further out or in depending on the combination. This article explains it:
https://www.sheldonbrown.com/bbtaper.html

 

[rogerzilla]

Big lockring spanner for the LH side (the cup itself won't be very tight) and, for the RH side, a fixed cup spanner with a mallet on the end if necessary.

 

[cimh]

Chris S. and Rogerzilla thank you both I’ll report back how I get on.

 

[T4tomo]

Sounds like its safest to try open up and check / grease the current bb than totally swap it out.

Finally (I hope), if I did manage to remove the bb completely would the threads in the frame still be compatible with the standard JIS bb sold for bromptons?

That is a sensible plan. The only reason to replace the BB if it isnt causing trouble would be if the new crank set needs a different length spindle to what's already in it. In terms of Brompton specific you can only buy the new spider crankset now (i think) vs the older one piece model (which is no bad thing, as the one piece was susceptible to failure).

Bromptons have quite a long spindle to cope with the fold, I'm not sure if your 30yr old model has same length spindle as the new ones, but I suspect it probably does, a Brompton were always pretty good at backwards compatibility for any upgrades.

One of the Brommie "experts" might be able to confirm..

 

[12boy]

Another option for the side with the nut is to put it in a table vise and use the frame itself as the lever. As far as I am concerned Shimano cartridge bearing BB will provide years of trouble free service and they are not expensive. After you get the current BB apart you may find pitting in the bearing surfaces anyway.

 

[berlinonaut]

That is a sensible plan. The only reason to replace the BB if it isnt causing trouble would be if the new crank set needs a different length spindle to what's already in it. In terms of Brompton specific you can only buy the new spider crankset now (i think) vs the older one piece model (which is no bad thing, as the one piece was susceptible to failure).

Bromptons have quite a long spindle to cope with the fold, I'm not sure if your 30yr old model has same length spindle as the new ones, but I suspect it probably does, a Brompton were always pretty good at backwards compatibility for any upgrades.

One of the Brommie "experts" might be able to confirm..

Extract from Brompton's data sheet "dscrankset":

• 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 according to Brompton mounting a JIS Spider Crankset to an ISO Bottom Bracket (like the OP wants potentially to do) ist not recommended. The other way round (ISO cranks to JIS bottom bracket) is possible, though not preferable.

 

[cimh]

Thank you all so much. Tonight the bb was removed with much less difficulty than I feared (lockring with a hammer and screwdriver) (fixed cup with a plumbing wrench) all with liberal amounts of wd40 and very little force. It was all fairly dry inside with some rust on the ball races and slight pitting in the cups. So I wll replace with the recomended 119mm JIS bb and a new crankset, sprocket and chain.

Very satisfying . . . so far

 

[T4tomo]

Thank you all so much. Tonight the bb was removed with much less difficulty than I feared (lockring with a hammer and screwdriver) (fixed cup with a plumbing wrench) all with liberal amounts of wd40 and very little force. It was all fairly dry inside with some rust on the ball races and slight pitting in the cups. So I wll replace with the recomended 119mm JIS bb and a new crankset, sprocket and chain.

Very satisfying . . . so far

See, I knew someone like @berlinonaut would know!! My chainset replacement happened pre 2013.