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Cranks Bottoming out on BB --- wont spin. ISIS

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Cranks Bottoming out on BB --- wont spin. ISIS

Old 07-25-13, 09:42 AM
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jeremyb
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Cranks Bottoming out on BB --- wont spin. ISIS

I am trying to install a FSA Carbon Pro Compact ISIS crank. I have a 108mm ISIS BB that I thought was the right size.

When I tighten the drive side down, the crank bottoms out on the BB bearings and then the crank doesnt spin at all. Am I doing something wrong or do I just need a longer BB axle like a 113mm?

I emailed FSA, no response yet. These cranks are about 4 years old so couldnt find technical info on their website. Thanks for any help!
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Old 07-25-13, 10:07 AM
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Originally Posted by jeremyb View Post
I am trying to install a FSA Carbon Pro Compact ISIS crank.
I have a set of those that I ran for ~6 years.

I have a 108mm ISIS BB that I thought was the right size.
ISIS bottom bracket lengths are standardized for the application. Road doubles use a 108mm spindle which is the narrowest.

When I tighten the drive side down, the crank bottoms out on the BB bearings and then the crank doesnt spin at all. Am I doing something wrong or do I just need a longer BB axle like a 113mm?
The bottom bracket is the right length. Something is probably wrong with it, its installation, or maybe the bottom bracket shell width.

I emailed FSA, no response yet. These cranks are about 4 years old so couldnt find technical info on their website. Thanks for any help!
The cranks likely have nothing to do with it. The spindle has a crank stop 16mm in from the end which the crank arm must bottom on - otherwise it may not be square to the axis with that issue on the drive side producing chain ring wobble and perhaps derailleur setup issues. If the bottom bracket gets tight when that happens there's something wrong.

You might share what brand bottom bracket you're using and see if some one had similar issues with the combination. I used an American Classic bottom bracket with mine (they're rebuildable and light).

A couple other tangential notes:

1. You might need to torque to the high end of spec to get the crank arms to bottom correctly. My chain rings weren't running straight until I figured that out.

2. If you're using them with a 9-speed chain you might need thin (less than 1mm) spacers on one of the chain rings to avoid rub in the smaller cogs. I had no usable overlapping gears between rings until I observed that the rings on my FSA Carbon Pro Compact cranks were closer together than my Campagnolo cranks and spaced them back to that dimension. Le Tour makes 0.6mm spacers specifically for adjusting 10 speed cranks to 9 speed spacing.

Last edited by Drew Eckhardt; 07-25-13 at 10:17 AM.
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Old 07-25-13, 10:13 AM
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Originally Posted by Drew Eckhardt View Post
ISIS bottom bracket lengths are standardized for the application. Road doubles use a 108mm spindle which is the narrowest.



The bottom bracket is the right length. Something is probably wrong with it, it's installation, or maybe the bottom bracket shell width.



The cranks likely have nothing to do with it. The spindle has a crank stop 16mm in from the end which the crank arm must bottom on - otherwise it may not be square to the axis with that issue on the drive side producing chain ring wobble and perhaps derailleur setup issues. If the bottom bracket gets tight when that happens there's something wrong.

You might share what brand bottom bracket you're using and see if some one has similar issues.

As a foot note if you're using them with a 9-speed chain you might need thin (less than 1mm) spacers on one of the chain rings to avoid rub in the smaller cogs. I had no usable overlapping gears between rings until I observed that the rings on my FSA Carbon Pro Compact cranks were closer together than my Campagnolo cranks and spaced them back to that dimension.


It's a Crank Brothers Cyan BB ----- it has a spacer for 68 and 73 BB shells ---- I tried both and same issue. I'll measure the actual BB shell tonight. The seller told me it was an ISIS crank ---- I know this crank also came in Octalink ---- is it possible that's the issue? Would an Octalink crank even fit onto an ISIS BB? It slid on easy, didnt have to force it on.

The BB axle spun freely before the cranks were installed ----- I installed non-drive side first and that didnt bottom out.
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Old 07-25-13, 10:21 AM
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Originally Posted by jeremyb View Post
It's a Crank Brothers Cyan BB ----- it has a spacer for 68 and 73 BB shells ---- I tried both and same issue. I'll measure the actual BB shell tonight. The seller told me it was an ISIS crank ---- I know this crank also came in Octalink ---- is it possible that's the issue? Would an Octalink crank even fit onto an ISIS BB? It slid on easy, didnt have to force it on.
Octalink uses eight splines like the name implies.

ISIS has ten.

You're not going to interchange them without using a very big hammer or hydraulic press.
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Old 07-25-13, 10:23 AM
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Thanks, I'll try again tonight, maybe take some photos too. I've installed a lot of bottom brackets and never had this issue.
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Old 07-26-13, 10:57 PM
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Originally Posted by Drew Eckhardt View Post
I have a set of those that I ran for ~6 years.



ISIS bottom bracket lengths are standardized for the application. Road doubles use a 108mm spindle which is the narrowest.



The bottom bracket is the right length. Something is probably wrong with it, its installation, or maybe the bottom bracket shell width.



The cranks likely have nothing to do with it. The spindle has a crank stop 16mm in from the end which the crank arm must bottom on - otherwise it may not be square to the axis with that issue on the drive side producing chain ring wobble and perhaps derailleur setup issues. If the bottom bracket gets tight when that happens there's something wrong.

You might share what brand bottom bracket you're using and see if some one had similar issues with the combination. I used an American Classic bottom bracket with mine (they're rebuildable and light).

A couple other tangential notes:

1. You might need to torque to the high end of spec to get the crank arms to bottom correctly. My chain rings weren't running straight until I figured that out.

2. If you're using them with a 9-speed chain you might need thin (less than 1mm) spacers on one of the chain rings to avoid rub in the smaller cogs. I had no usable overlapping gears between rings until I observed that the rings on my FSA Carbon Pro Compact cranks were closer together than my Campagnolo cranks and spaced them back to that dimension. Le Tour makes 0.6mm spacers specifically for adjusting 10 speed cranks to 9 speed spacing.
Update: I contacted FSA they said to use a 113mm BB, bought one and installed tonight, works fine!
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Old 07-27-13, 01:54 AM
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i think so,I've installed a lot of bottom brackets and never had this issue.thanks
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