Shimano FC-MC16 Spindle length?

dmorton

Can anyone help me out with the required bottom bracket spindle length for some old Shimano Alivio FC-MC16 cranks?

I'm swapping bits to another frame, BB is stuck fast in original frame...although its working fine. Looked online and I can get a replacement Shimano UN26 BB for £10, however as the original is stuck fast can't find out what spindle length it is.... guesstimates with a ruler look about 113mm, although it could be 110mm. Both BB shells are 68mm

I could instead replace the whole lot....

Chunkers1980

Yeah get yourself a HTII deore. Less than 50 quid for the lot.

cooldad

You need one that gives the right chainline for the new frame.

nicklouse

depending on what chain line you want 110 - 113mm

so have a measure.

http://sheldonbrown.com/bbsize.html

dmorton

Here's where I'm a bit confused...

So the spindle length is determined by the frame, not the cranks to be used?

£50 is a lot more than £10.....

nicklouse

dmorton wrote:

Here's where I'm a bit confused...

So the spindle length is determined by the frame, not the cranks to be used?

£50 is a lot more than £10.....

nope it is determined by the chain line. that depends on what the frame needs and what the cranks give.

older frames had a nominal 47mm chain line newer ones have 50mm and there are other posibilities.

dmorton

So it's a function of the cranks AND frame......

The 'new' frame is a 2009 Scott Contessa 40.....any ideas?

EDIT: Nick I missed your post with the link to Sheldon Brown... checking that out now, cheers

dmorton

After looking at both Sheldon Brown and Park Tools, I understand what the chainline is and how I can measure the new frame's chain line at the rear. That will give me the rear chain line. However, how do I then know which BB spindle length will give me a matching chainline at the front?

Do I go back to the old bike, stick the crank back on and measure the front chain line on that? Then if that's say 45mm and the old spindle length is 113mm, then I know 113mm and these cranks give me 45mm at the front..... if that's then comparable to the new rear chainline then I need a new 113mm BB? Or if the new rear chainline is shorter I go with 110mm....

I've also thought I can short cut this. The rear wheel and cassette are from the same bike the cranks are coming from. The new and old BB shells are the same width (68mm) so if the new and old frame have the same spacing at the rear dropouts, then I need the same spindle length for the new frame as is on the old frame..... the seat tubes are the same diameter so the front derailleur should line up ok too.