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Discussion Starter · #1 ·
Usually more of an issue on a single speed, I guess. New-to-me XT crank with brand new chain ring has a lot of runout in big ring. It's hard to finesse the FD to keep the ring chain from rubbing the cage on BOTH sides. Not a problem in the middle ring. Can I resolve this issue with a spacer on one or two arms or maybe a vice grip/hammer intervention? Has anyone experienced this problem?
 

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Are you saying the you contact one side of the derailleur while in the small cog, and the other while in the large cog....

Or are you claiming that your large ring is so out of flat (planar) that you contact both sides of the derailleur simply by turning the cranks in a full revolution (without changing cogs)?


Are you sure that your front derailleur is installed correctly (height, angle)? Are you sure that your bb spindle is not causing the runnout..ie spacer set-up is correct and the spindle is not able to move side to side?

Lastly, I dont think it would be a big surprise to buy used cranks and have the big ring bent...That is the first part that would contact something (log, rock, etc) and see damage.
 

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Discussion Starter · #3 ·
The big ring travels side to side as it revolves.

davep said:
Or are you claiming that your large ring is so out of flat (planar) that you contact both sides of the derailleur simply by turning the cranks in a full revolution (without changing cogs)?
Exactly that. I had a road bike once that did this too, but not so much. I only noticed it when looking down on it--it didn't rub. From what I understand, some runout is normal except, ideally, in SS or track cranks.

davep said:
Lastly, I dont think it would be a big surprise to buy used cranks and have the big ring bent...That is the first part that would contact something (log, rock, etc) and see damage.
Everything is tight and adjusted, it's not the spindle moving in the BB shell. The big ring is brand new so it isn't bent.

My FD might be a smidge too high on the ST. I'll check that!
 
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