Square taper bb size and chainset

[C R]

Hi all.

I have started looking for a replacement for my bottom bracket, but seem like things aren't as straightforward as I expected. My bike has a 68mm shell, but the spindle length is 136mm, size 3RR according to Sheldon Brown. I have been looking, and I can't find a UN55 with a spindle that size. My bike is probably 25 years old, and that might explain the odd size of the spindle.

My question is, is it the chainset that determines the spindle size? If so, does that mean I will need to change the chaiset if I can't get the correct size spindle?

 

[Smokin Joe]

Yes, the chainset does determine the spindle length.

 

[midlife]

That seems quite long, is it a triple? What is the make of the chainset.

 

[Milkfloat]

Phil Wood does a 135mm, but they are not cheap.

 

[iluvmybike]

The longest square tapers ones are 127.5mm. Have you removed the crankset and measured the actual spindle length? The only 136mm one I have ever heard of was a cottered type

 

[Hugh Manatee]

I'm very curious as to the chainset as well. I have a few old mountain bikes and as mentioned by others, the axle length of the old DX and XT units max out well before 136mm.

 

[tyred]

If you look on St John Street cycles or on Ebay you should be able to buy the correct spindle, or something very close too it, you could probably go a few mm longer if need be but not shorter as the chainset will probably catch the frame. The cups are still easily available if you need them.

I had this recently with my old mountain bike as I would really have liked a sealed cartridge but couldn't find one in the right dimensions so rebuilt it with new parts in the old fashioned way. If you're doing this, replace the caged bearings which will probably come with the new cups with loose ones as they will last longer - you need twenty-two 1/4" ball bearings.

 

[C R]

If you look on St John Street cycles or on Ebay you should be able to buy the correct spindle, or something very close too it, you could probably go a few mm longer if need be but not shorter as the chainset will probably catch the frame. The cups are still easily available if you need them.

I had this recently with my old mountain bike as I would really have liked a sealed cartridge but couldn't find one in the right dimensions so rebuilt it with new parts in the old fashioned way. If you're doing this, replace the caged bearings which will probably come with the new cups with loose ones as they will last longer - you need twenty-two 1/4" ball bearings.

Thanks, checked but unfortunately they don't have the 3RR axle. My problem is the cups are showing signs of needing retirement, at least the adjustable one, the fixed one I can't tell for sure. The spindle seems ok, some sign of wear but not too bad. Perhaps I'll just go with changing the cups for the time being and then replace the whole bb when it comes to replace the chainset.

 

[C R]

I'm very curious as to the chainset as well. I have a few old mountain bikes and as mentioned by others, the axle length of the old DX and XT units max out well before 136mm.

I don't know what the chaiset make is, I haven't seen any markings identifying the manufacturer. It is a double, with riveted chainrings, steel as far as I can tell, 48T and I think 42T, though I haven't actually checked the size of the small one.

 

[C R]

The longest square tapers ones are 127.5mm. Have you removed the crankset and measured the actual spindle length? The only 136mm one I have ever heard of was a cottered type

Yep, total length is 136, this corresponds to the old Japanese 3RR size according to Sheldon Brown:
https://www.sheldonbrown.com/bbsize.html

 

[midlife]

Is it a cottered chainset?

 

[C R]

Is it a cottered chainset?

Square taper.

 

[tyred]

In my case, (early 90s low end MTB), I had a further complication of 70mm shell and the only cartridge BBs I could see in my size were Italian threaded. My cups were definitely BSA. I think mine was 136mm too IIRC.

 

[raleighnut]

The cups might be OK, don't forget the bearings only make contact on a very narrow 'track'.

 

[C R]

In my case, (early 90s low end MTB), I had a further complication of 70mm shell and the only cartridge BBs I could see in my size were Italian threaded. My cups were definitely BSA. I think mine was 136mm too IIRC.

I found a 70x134 spindle in sjs, no good for me though, I need 68.