Bottom brackets

[Johnymak]

If a square taper bb has allready been fitted to a frame
Will any square taper crank fit it

Thanks in advance

Merry Xmas and happy New year

 

[Rickshaw Phil]

No unfortunately. Cranks usually require a specific length of BB axle so that the chainrings line up correctly. You might be lucky enough that the BB matches your chainset but really you need to measure the axle length or take it out and see what's marked on the shell to be certain.

 

[midlife]

There is also the conundrum of ISO and JIS design plus the odd Suntour /Ofmega wild card lol

 

[Ajax Bay]

If a square taper bb has allready been fitted to a frame
Will any square taper crank fit it

Read this about ISO and JIS. Yours is most likely JIS.
https://www.sheldonbrown.com/bbtaper.html
Assuming a JIS square taper BB, a JIS square taper crankset will fit. The issue is whether the chainline will be correct (middle ring in line with middle sprocket).
Without disagreeing with the above posts, broadly if you're replacing a triple (or a double) with the same, you have a good chance that the crankset will fit and the chainline will be OK.
Chain lines: https://www.sheldonbrown.com/chainline.html

 

[fossyant]

Axel length can vary. I switched from an old Deore LX to a newer Deore LX triple. It needed a shorter axel BB as the newer cranks were a lower profile.

Don't worry too much.

 

[woodbutcher]

No unfortunately. Cranks usually require a specific length of BB axle so that the chainrings line up correctly. You might be lucky enough that the BB matches your chainset but really you need to measure the axle length or take it out and see what's marked on the shell to be certain.

I am (attempting) building up a Vitus 979 frame which already has a Stronglight BB fitted . It is my intention to fit a Shimano tricolour (double) crankset . Is it likely that l might have an issue with the axel length or am l panicking too early ? PS. l cant figure out how to get the S'light BB apart !

 

[chriscross1966]

I am (attempting) building up a Vitus 979 frame which already has a Stronglight BB fitted . It is my intention to fit a Shimano tricolour (double) crankset . Is it likely that l might have an issue with the axel length or am l panicking too early ? PS. l cant figure out how to get the S'light BB apart !

Stronglight bottom brackets tend to be from the cheaper end of the scale. What format is it and what is the bottom bracket size?... Shimano BB's are pretty good for the price and you shouldn't find it hard to match one to your new cranks.

 

[woodbutcher]

Stronglight bottom brackets tend to be from the cheaper end of the scale. What format is it and what is the bottom bracket size?... Shimano BB's are pretty good for the price and you shouldn't find it hard to match one to your new cranks.

I will unscrew the Stronglight and take a photo later today with size etc. The Vitus B/B shell is threaded all the way through to match the S'light , so l don't know if that will be a problem if l swap to Shimano !

 

[woodbutcher]

This is it size 35 x 100 the axel moves smoothly and in any case l cant see how the thing comes to pieces , probably best left alone !

 

[rogerzilla]

Manufacturing tolerances vary a lot too. I have cranks and BBs from the same manufacturer (hence the taper *should* be matched) where the amount by which the crank slides onto the taper is very different. My TA track cranks slide so far onto the TA Axix BB that there is only about 2mm between the end of the axle and the seat for the crankbolt. My Shimano cranks are nothing like that, and nor are Sugino cranks on Shimano or Tange BBs (all JIS).

 

[midlife]

Just out of curiosity Mr Woodbutcher does a magnet stick to that Stronglight axle?

 

[woodbutcher]

Just out of curiosity Mr Woodbutcher does a magnet stick to that Stronglight axle?

I will try that tomorrow ....hadn't thought of the experiment . Thanks for the suggestion , l will report back !

 

[woodbutcher]

Just out of curiosity Mr Woodbutcher does a magnet stick to that Stronglight axle?

I see where your question is going and yes it is magnetic so l checked the very high spec Vitus 992 and that one is non magnetic so lm thinking titanium ?

 

[midlife]

That's what I was thinking too. I have come across high end sealed Stronglight bottom brackets with titanium axles..... Long time ago though lol.

 

[woodbutcher]

That's what I was thinking too. I have come across high end sealed Stronglight bottom brackets with titanium axles..... Long time ago though lol.

So was it simply about saving a few grams of weight or are there performance benefits . ?