Bottom Bracket for C456

kieron_67

Hi guys

Ive recently brought a carbon 456 and am looking at putting my shimano xt M571 3 speed crankset on to it,

The problem is i dont know how to work out the bottom bracket size and the data sheets on the crankset dont seem very informative to me.

So does anyone have any ideas on the axle lenght i will need for the BB, i know its a 73mm English but not sure on the axle lenght,

Thank you

bennett_346

I'm not really sure what you are asking but if you know it's a 73mm then put a 68/73mm bottom bracket in with the correct spacers in the data sheet, usually none for 73 but you may as well check. If by axle you mean the crank axle then they're all the same if they're HTII so with the right spacers installed it will fit.

Chunkers1980

Are you sure that's an XT?

If I search on the M571 code I get an octalink LX crankset. In which case I recomend taking it out, reading the code and buying like for like.

benpinnick

I presume you typo'd and meant M771? A fairly recent XT 9 speed crankset. Thats hollowtech II, and you need 1 spacer on the drive side only.

kieron_67

hmmm i'm not sure it says M571 on the back of the arm but the decals on it are the XT decals.

I just need the lenght of the axle for the BB, its an old hollowtech design not the newer one.

bennett_346

How about you measure it?

kieron_67

i dont know how i can measure it when its a brand new frame and never had a bb fitted to it, the frame i am taking the cranks from is an entirely different size

kieron_67

This is the BB i am looking at

http://www.wiggle.co.uk/shimano-deore-e ... m-bracket/

I just dont know how to calculate the axle lenght, ive contacted On-one but so far no replies

benpinnick

Youd be better buying new cranks for that money!

Chunkers1980

Yeah - that's a crazy price.

You can get a Deore HTII set with BB for about £55. If your rings aren't worn they may just fit striaght on the HTII chasis.

New BB from there on in will set you back less than £15, and kept going for longer by stuffing grease into them, as I've just discovered.

Chunkers1980

Oh and you remove the need to know anything about axel length (shell width) until you fit, then just workout how many (if any) spacers to use each side.

bennett_346

Yes but surely you have the BB that you want to buy that to replace, which you could measure/read of the info if its printed on it.

kieron_67

yes i do have the bb but its a 68mm one so i thought the axle lenght might not be the same

bennett_346

Got ya. Well i think i'd just buy a new set of cranks personally, you're going to have to in the end anyway!

Anonymous

Well starting with what's easy - the C456 is a 73mm BB shell.

Existing crankset, what size shell was the frame it came from, and did it have spacers?

If it was 73 also, no spacers, then all is good, get 68/73 BB no spacer required, fit the cranks.

If it was 68 and had spacers, get 68/73 BB no spacer required, fit the cranks - I think? (i.e. crank axle length will be right for 73 as the spacer(s) were to fit it to 68).

If it was anything else, then you have a problem.

Whatever the case, I'd have thought just get a 68/73 BB, forget the spacers, see if the crank fits.

bennett_346

deadkenny wrote:

Well starting with what's easy - the C456 is a 73mm BB shell.

Existing crankset, what size shell was the frame it came from, and did it have spacers?

If it was 73 also, no spacers, then all is good, get 68/73 BB no spacer required, fit the cranks.

If it was 68 and had spacers, get 68/73 BB no spacer required, fit the cranks - I think? (i.e. crank axle length will be right for 73 as the spacer(s) were to fit it to 68).

If it was anything else, then you have a problem.

Whatever the case, I'd have thought just get a 68/73 BB, forget the spacers, see if the crank fits.

He was and wants to use Octalink with it

kieron_67

ive removed the bb from the donor frame and its a 68x113,

if i get a 73x113 will that be ok for the new frame?

thanks

leaflite

As mentioned you're probably better off getting a nice shiny new deore crankset.

supersonic

Download the tech manual for the crank you have and look what length axle you need for a given chainline.

If you go HT2, the BB is included with spacers.