Bottom Bracket BSA 1.37 vs BSA 1.375

[Andy in Germany]

I'm trying to fit a new BB onto a bike and it won't fit. On closer inspection the old BB is a BSA 1.37 and the new one is a BSA 1.75" Nowhere can I find a BSA 1.37" BB on sale or even a reference to the different sizes. Am I missing something or is this a really unusual size?

 

[figbat]

The BSA thread is 1.37" x 24 tpi - any BSA BB you buy should be this. I'm not aware of a BSA 1.75", so not sure what your new BB is?

 

[FrankCrank]

What bike is it?

 

[Ajax Bay]

I'm trying to fit a new BB onto a bike and it won't fit. On closer inspection the old BB is a BSA 1.37 and the new one is a BSA 1.75" Nowhere can I find a BSA 1.37" BB on sale or even a reference to the different sizes. Am I missing something or is this a really unusual size?

The BSA / British and ISO standards are interchangeable:
1.370" X 24 tpi
1.375" X 24 tpi
Vast majority of threaded BB shells will take this (68mm for road, 73mm for MTB).
UN-55 superseded by UN-300 and many other cartridge BB makes (and spindle lengths).
Since the 1.37" refers to the BB shell diameter I'm not surprised a 1.75" BB will not fit.
Edit: I realise your text 1.75" is a typo for 1.375" - see line one above.
Bike Gremlin for more and pictures.

 

[Andy in Germany]

The BSA thread is 1.37" x 24 tpi - any BSA BB you buy should be this. I'm not aware of a BSA 1.75", so not sure what your new BB is?

The new one is a normal BB, the old one is a tiny bit smaller and fits the frame.

 

[Andy in Germany]

The BSA / British and ISO standards are interchangeable:
1.370" X 24 tpi
1.375" X 24 tpi
Vast majority of threaded BB shells will take this (68mm for road, 73mm for MTB).
UN-55 superseded by UN-300 and many other cartridge BB makes (and spindle lengths).
Since the 1.37" refers to the BB shell diameter I'm not surprised a 1.75" BB will not fit.
Edit: I realise your text 1.75" is a typo for 1.375" - see line one above.
Bike Gremlin for more and pictures.

I'm not sure what's causing the problem then. The standard cartridge I've ordered (and fitted to other bikes) is too big to fit into this BB thread.

 

[FrankCrank]

Again, what bike is it?
If it happens to be an old Raleigh, or a variant of, from some years back, a standard BB will screw in a couple of threads, then no more.
I believe same goes for French and Italian bikes, but have no experience of these.

 

[Ajax Bay]

Again, what bike is it?
If it happens to be an old Raleigh, or a variant of, from some years back, a standard BB will screw in a couple of threads, then no more.

But the BB Andy's replacing is an "old BB - BSA 1.37".

 

[Ajax Bay]

Think we need pictures Andy (old and new, with writing), or at least share what the frame is, if you can tell.

 

[All uphill]

The late great Sheldon Brown says that 1.370" is the British Standard while the 1.375" is the ISO standard. He also says that they are interchangeable.

On the other hand a Bikeradar article on BBC says 1.375" is the Italian standard, but that has conventional (righty- tighty) threads on both sides.

I'm not sure if that helps...

 

[wafter]

Could possibly be a tolerance-stacking issue; BB at the fat end of the range and BB shell at the tight end... might be worth trying to find the actual dims of each standard and measure the examples in hand.

 

[Andy in Germany]

Again, what bike is it?
If it happens to be an old Raleigh, or a variant of, from some years back, a standard BB will screw in a couple of threads, then no more.
I believe same goes for French and Italian bikes, but have no experience of these.

It's made by Gudereit. A pity, as it's a nice bike, but we'll strip it for parts and scrap the frame next week.

 

[wafter]

If the BB shell is the only problem, consider my tolerance-sticking suggestion above. Also worth trying other BBs, chasing out the threads with a BB tap (of you have one) or opening up the threads in the frame slightly by applying abrasive paste to them and working the old, knackered shells in and out