crank question.... and bottom bracket

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crank question.... and bottom bracket

Postby pembo6 » Tue Dec 04, 2012 1:25 am

Hi. I am working on my first fixie project. I am goingg to buy a new crank online. My existing bottom bracket has square taper axle with the older style nuts (not newer Allen bolts) holding on the crank arms.

If I purchase a new cranksset for square taper, will it fit the larger nuts? Or do the newer cranksets only fit the axles with the smaller Allen bolts. My existing BB is the right size (68mm). I am just worried that the nuts won't fit into a new crank arm.
Or will I need to also purchase a new BB?

I hope I have explained that clearly??
Last edited by pembo6 on Tue Dec 04, 2012 2:07 pm, edited 1 time in total.
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by BNA » Tue Dec 04, 2012 2:50 am

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Re: crank question

Postby Dan » Tue Dec 04, 2012 2:50 am

They'll fit.
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Re: crank question

Postby BRLVR.v2 » Tue Dec 04, 2012 11:51 am

Dan wrote:They'll fit.

But the issue will be the axle length, if its an old road double it maybe toolong. A new bb that matches your crankswill get a better chainline. Have a look at sheldon brown's info . 68 mm is the shell width,the axles come in many lengths,and thats the important bit
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Re: crank question

Postby Dan » Tue Dec 04, 2012 12:40 pm

indeed...
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Re: crank question

Postby slidetaker » Tue Dec 04, 2012 12:41 pm

some deals combine BB with crank so the package will tell you what exactly is the chainline....(around 42mm)...

which you can aim to match with the cog in the rear wheel....
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Re: crank question

Postby Dan » Tue Dec 04, 2012 12:49 pm

All redundant until OP has a wheelset. For example, running a road rear with a spacer kit means its likely that any english thread BB will work, as the chainline can be adjusted with the spacers on the freehub. Different story with a track/fixed rear, which is what Dave was alluding to. In any case, original question was whether the cranks bolts would work with the new cranks....
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Re: crank question

Postby pembo6 » Tue Dec 04, 2012 2:04 pm

Thanks for the comments.

So it seems that the cranks will fit my existing BB, but it may not be at the ideal chainline. It is an old road double chainwheel.

I will be running a new flip-flop rear wheel/ hub (in the mail) and will be using a fixed track cog. So a little limited in changing the chainline at the rear (without moving wheel over and re-dishing).

It sounds like my best option is to get the new crankset and check the chainline. Fingers crossed it will be OK. If not, I will measure the BB/spindle width and see what I need to get the correct chainline.

The crank I am looking at does specify the chainline (42.5 I think??) but it does not specify what BB size that is for. The specs are......

Chainline: 43.5mm
BB Axle: Square (103) NOT included

Is "103" the BB/spindle length? How can it state the chainline without knowing what BB is being used?

Thanks again for your help.
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Re: crank question

Postby Dan » Tue Dec 04, 2012 2:32 pm

pembo6 wrote:
Chainline: 43.5mm
BB Axle: Square (103) NOT included

Is "103" the BB/spindle length? How can it state the chainline without knowing what BB is being used?



that's the chainline you'll get using a bottom bracket with an axle/spindle length of 103mm - cranks can only sit so far in on the axle before they bind, as they're tapered. Look at the link to Sheldon posted earlier. If you want a chainline that's lesser, you need to get a shorter axle, and vice versa.
Last edited by Dan on Tue Dec 04, 2012 3:35 pm, edited 1 time in total.
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Re: crank question.... and bottom bracket

Postby BRLVR.v2 » Tue Dec 04, 2012 3:21 pm

you can also look at removing the axle and flipping it as quite often they are longer on the drive side to allow for the two rings. This may bring it in a little closer. This works , I've done it before in the past on quick flip conversions.
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Re: crank question.... and bottom bracket

Postby Mulger bill » Tue Dec 04, 2012 9:47 pm

It'd be worth trying the single ring in the small ring position too, it won't look as neat but it may solve the problem.
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
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Re: crank question.... and bottom bracket

Postby BRLVR.v2 » Wed Dec 05, 2012 6:52 am

Mulger bill wrote:It'd be worth trying the single ring in the small ring position too, it won't look as neat but it may solve the problem.


I think OP is purchasing a new single ring specific crank which only has one mounting option any way.
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Re: crank question.... and bottom bracket

Postby Mulger bill » Wed Dec 05, 2012 10:38 pm

BRLVR.v2 wrote:
Mulger bill wrote:It'd be worth trying the single ring in the small ring position too, it won't look as neat but it may solve the problem.


I think OP is purchasing a new single ring specific crank which only has one mounting option any way.

:oops: Comprehension fail.
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
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Re: crank question.... and bottom bracket

Postby BRLVR.v2 » Thu Dec 06, 2012 9:49 am

Mulger bill wrote:
BRLVR.v2 wrote:
Mulger bill wrote:It'd be worth trying the single ring in the small ring position too, it won't look as neat but it may solve the problem.


I think OP is purchasing a new single ring specific crank which only has one mounting option any way.

:oops: Comprehension fail.


Old age,bud..... :wink:
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