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Discussion Starter · #1 ·
Hey everyone,

I have a Trek (can't remember the model) that my brother just gave to me. I have to change the crank set on it. Where you screw in the pedal to the arm is stripped. I actually have another crank set at home that I can use. But when I put it on, the crank teeth hits the bracket that the derailleur is mounted to.

This derailleur bracket is attached to the bottom bracket. So I took the bracket off and was going to put a post mounted derailleur on, but I am unsure if it will work.

Any thoughts?

Thanks in advance,
Kevin
 

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Different cranksets often require different bottom brackets. Example: One may be designed for a 108mm spindle and the other may require a 116mm spindle to maintain the same chain line. I'm guessing that your good crankset may require a longer bb since it's hitting the bracket.

As far as I know most front derailleurs work on a 50mm chain line. You can measure this. It's the distance from the center of the seatpost to the middle ring.

Sheldon Brown: http://www.sheldonbrown.com/chainline.html
 

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Discussion Starter · #3 ·
Thanks for the info. But if I am using the same derailleur and the same bottom bracket how do I determain what size of crank I need to buy?

Kevin
 

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The bb requirement will be available from the manufacturer. Some stores list the details in the product info. Example: http://www.niagaracycle.com/product_info.php?products_id=6363. The product info states "use 110-113mm spindle".

You can work backwards by measuring your bb spindle. Then look for cranks that use that length. I don't have calipers to accurately measure something like that, so I would use a big C-clamp (then measure the clamp) or use a couple of squares.

Good luck with it.

edit: Sheldon Brown lists some spindle lengths for various cranksets: http://www.sheldonbrown.com/bbsize.html
 

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Discussion Starter · #5 ·
Thanks for much for all the feedback and help. I put a regular clamp derailleur on and there is no issues. Everything is working perfectly.

Thanks again.
Kevin
 
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