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Crank shaft replacement

Old 02-25-21, 02:35 PM
  #1  
Drewnash1988
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Crank shaft replacement

Hi all,

Newbie cyclist.

I have a cannondale caadx-2 gravel bike

The pedals were put on incorrectly, which ruined the thread on one of the cranks. It is a FSA crank, 40t and is 172.5mm but I canít source a replacement part anywhere. Is there a alternate brand crank set that could be used instead?

Thanks

Drew
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Old 02-25-21, 02:48 PM
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Iride01
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New bike? Maybe go back to the shop and they'll have some pity on you and get something that works for a decent price. If you change to a different brand of crank you might have to change the BB.

They can at least tell you what model crank that is. Maybe a FSA Gossamer PRO? That will mean you need to look for a crankset that also has a 30mm diameter spindle.
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Old 02-25-21, 03:00 PM
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Originally Posted by Iride01 View Post
New bike? Maybe go back to the shop and they'll have some pity on you and get something that works for a decent price. If you change to a different brand of crank you might have to change the BB.

They can at least tell you what model crank that is. Maybe a FSA Gossamer PRO? That will mean you need to look for a crankset that also has a 30mm diameter spindle.
Thank you, no luck with the shop. Evans Cycles are not in a good way at the moment. Itís a FSA Vero pro.
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Old 02-25-21, 03:10 PM
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So you're talking about the crank arm, not the crank spindle? And what got messed up is the pedal threads on one of the arms?

Something to try before giving up on that arm: take the correct pedal for whatever arm is involved and very carefully begin to thread it in, correct rotation for that arm, from the back side. If you can get it started from the back side - and are sure it's starting to thread in and not cross-threaded, then you might be able to repair the threads by threading it in all the way. Sometimes the threads are only messed up partially, and this will work. The threads in the crank arm are relatively soft aluminum, while the threads on the pedal are steel. They will cut the aluminum threads (which is how they get messed up if incorrectly installed) and can also "chase" (clean up, repair) the threads if the damage isn't total.

You could also check into enlarging the hole in the crank arm and installing threaded inserts - "helicoil" type things.
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Old 02-25-21, 03:15 PM
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Originally Posted by Camilo View Post
So you're talking about the crank arm, not the crank spindle? And what got messed up is the pedal threads on one of the arms?

Something to try before giving up on that arm: take the correct pedal for whatever arm is involved and very carefully begin to thread it in, correct rotation for that arm, from the back side. If you can get it started from the back side - and are sure it's starting to thread in and not cross-threaded, then you might be able to repair the threads by threading it in all the way. Sometimes the threads are only messed up partially, and this will work. The threads in the crank arm are relatively soft aluminum, while the threads on the pedal are steel. They will cut the aluminum threads (which is how they get messed up if incorrectly installed) and can also "chase" (clean up, repair) the threads if the damage isn't total.

You could also check into enlarging the hole in the crank arm and installing threaded inserts - "helicoil" type things.
Yes, just the arm. Thank you, really helpful. I think I need to not try and fix it myself and just give in and take it to another shop.
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Old 02-25-21, 03:16 PM
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Oh, an older square taper BB. https://shop.fullspeedahead.com/en/t...is-crankset-1x

That might make other brands of crank a little easier swap then. Just look for something that is JIS Square taper.

Back in the days I used square tapers, it was always a toss up whether another brands crank would sit the same on the BB and give you the same chain line.

BB's typically don't cost much. If that's a threaded bb then you can change it out and get whatever crankset you want that fits that shell. But then you do also either have to have the tools and knowledge or pay a bike shop to change it out.

As Camilo suggested, running the pedal into the crankarm through the backside might fix the buggered threads on the crank arm, but only if they can reach completely through to the other side. Mine don't go completely through so I've always been doubtful how many this will ever help since it usually only the starting threads that are messed up.

Last edited by Iride01; 02-25-21 at 03:22 PM.
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Old 02-25-21, 03:20 PM
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most bike shops and dedicated DIYers should be able to put a new coil in a crank arm. look up "how to repair pedal threads" and you'll find dozens of guides to fixing it. you might be able to tap new threads if the arm is not TOTALLY stripped out.
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Old 02-25-21, 04:01 PM
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Originally Posted by mack_turtle View Post
...you might be able to tap new threads if the arm is not TOTALLY stripped out.
Yabut remember that a tap can only remove metal, so the threads will likely be permanently weakened and more likely to fail. The Helicoil repair, on the other hand, will result in stronger threads than the original.
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