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Old 08-07-08, 05:44 PM   #1
Walter
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Chain rub on front derailleur

I need some advice and/or ideas.

I just swapped out a Campy Chorus (aluminum) crankset on my Reynolds 853 LeMond for a Zipp 300 (CF) set and cannot tune out a small amount of chain rub in the 53-12 combo.

Here's the specifics: The Campy Chorus was a 108mm square taper BB. I'm using a 108mm American Classic ISIS BB with the Zipp. These are the correct size BBs. I'm using a Centaur FD (clamp on).

My LBS installed the Zipp (I didn't have the right BB tool) and told me about the rub. I went to the Park Tools site and was able to get rid of much but not all of the rub and am pretty certain that adjusting the FD is not the answer but I'm willing to listen.

I've noticed that there's a "bulge" on the inside of the outside arm of the FD. I assume that's to aid shifting but it's where I'm getting the rub.

The Zipp crank arm is thicker than the aluminum Chorus.

If I adjust the High screw anymore the cage rubs on the crank arm and I can't have that.

Are there any answers or am I a victim of the FD design and the "chunkiness" of a CF crank arm (and if I am are there other FDs I should look at?)

Thanks
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Old 08-07-08, 07:37 PM   #2
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i'm not running nearly as high-end components, but i just had the problem with the little 'bulge' to aid shifting. i'm not too versed on road components, but the issue might be in the shifter, that's where mine was. just had to mess w/ the cable tension where it routed into the shifter, and it did the trick. is it possible your new Zipp FD is bent?
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Old 08-07-08, 08:42 PM   #3
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Where is the bulge? If it's towards the rear of the FD, try rotating the rear of the derailler towards your cranks and see if that gives you enough chain clearance without interfering with the cranks. If that doesn't work, it sounds like you just need a longer bottom bracket.

I have sort of the opposite issue on one of my bikes. I couldn't tune out a small amount of chain rub in my 30-27 gear combination. The front derailler was hitting the frame so no amount of adjusting the low stop screw would help. I ended up swapping out the front derailler from a 105 9 speed to a 105 10 speed (to solve a different issue) and I got lucky in that the new derailler had more inward travel before contacting the frame. No more chain rub!
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Old 08-07-08, 08:52 PM   #4
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Kind a very simplistic answer, based on your input, would be to try more tuning on the FD. Specifically, the height of the FD on the seatpost can make dramatic changes. Tweak the height and angle of the FD and see how that goes. Just keep in mind that each time you change height and/or angle, you must go through the whole FD alignment proceedure again. It's not all science. There is some amount of art to FD alignments and it's often worth a little experimentation to get better results. Be patient and keep trying. Just keep a close eye on exactly what you change and what the results are. Once you get the best results you can with height and angle tweaks, then fine tune with cable tension.


Here's the Park Tool proceedure:

http://www.parktool.com/repair/readhowto.asp?id=75

This is an excellent reference, but, as I have already stated, there is a certain amount of art to FD alignments. I've seen some really good mechanics use vastly different methods to get good results. Start with the Park and go from there.
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