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Old 05-02-04, 05:45 PM   #1
franklen
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Front Derailleaur and Chainrings out-of-line After BB Replacement

So after I took all the time to learn how, and to replace my cartridge bottom bracket, I hop back on this week to regain my commute, and I start to hear a slight click on each downward left side pedal. It contined the same for the next day and when I tried to discover the issue by simulating a pedaling on my porch I couldn't hear the sound. On closer inspection, I notice that my chain is slightly rubbing up against the derailleur cage at a certain cycle where my chainring has a slight bend to it. I can't adjust the derailleur in any further because the screw is at its limit.

Am I stuck at having to get new chainrings, or a new front derailleur, or is it the bottom bracket (a wrong fit)? Any help is appreciated, thanks.
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Old 05-02-04, 06:26 PM   #2
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Quote:
Originally Posted by franklen
So after I took all the time to learn how, and to replace my cartridge bottom bracket, I hop back on this week to regain my commute, and I start to hear a slight click on each downward left side pedal. It contined the same for the next day and when I tried to discover the issue by simulating a pedaling on my porch I couldn't hear the sound. On closer inspection, I notice that my chain is slightly rubbing up against the derailleur cage at a certain cycle where my chainring has a slight bend to it. I can't adjust the derailleur in any further because the screw is at its limit.

Am I stuck at having to get new chainrings, or a new front derailleur, or is it the bottom bracket (a wrong fit)? Any help is appreciated, thanks.
There's several possibilities. It would help if you could be more specific about exactly what crank and bottom bracket you have.
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Old 05-02-04, 07:28 PM   #3
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If the ONLY item you replaced was the BB, chances are you installed one with a slightly different spindle length from the original.
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Old 05-03-04, 08:31 AM   #4
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The screws only adjust the inner and outer limits of the cage travel. What you need to do is either tighten the fr der cable if the chain is rubbing against the inside of the cage, or loosen the cable if the chain is rubbing on the outside of the cage.
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Old 05-03-04, 09:23 AM   #5
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Wrong BB. As Fixer said. That was the only thing you changed. Look on the body of the old bb and compare it to the new one. You should see numbers such as 68 or 78, 112, 113, 115, 118 etc. The new bb should have the same numbers as the old one.

The only other possibility would be that you did not tighten the crank bolts enough. But you would know that soon as you rode.
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Old 05-03-04, 09:48 AM   #6
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The only other possibility would be that you did not tighten the crank bolts enough. But you would know that soon as you rode.
Unfortunately, that's not the only possibility that I can think of. That's why I asked for more information. If he has a splined crankset, if he tried to reinstall it without making sure that the splines were properly alligned, that's exactly what would happen. Tightening the crank bolts more in that case would assure that the crank was completely ruined.
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Old 05-03-04, 10:20 AM   #7
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Sounds like the BB is a slightly different spindle length. As for the limit screw, the tension on the cable may inhibit you from adjusting it any further. Go to http://www.parktool.com/repair_help/...railleur.shtml - this should help you out.

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Old 05-03-04, 10:29 AM   #8
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OK, I'll check if there is a model number/name of the BB when I get home as I still have the packaging (It is a cartridge type from Shimano however). Thing is, I couldn't identify what type of BB I was removing from any markings, I just couldn't find any (this is a Diamondback MTB 10+ years old that I inherited and this would be the first BB replacement on it). My LBS checked it out (couldn't find markings either) and ordered the replacement, so hope they got it right. When I put the old and new side by side to give it the once over check they seemed as close as could be without actually measuring the mm's.

As for the crank bolts, I used a torque wrench so am pretty confident I got them tight enough, and they haven't loosened or wobbled any yet anyhow. The right crank is factory whatever came with this bike. I am, I think, going to try adjusting the cable next before going through the trouble of taking out the BB again. This will be another first for me though, it seems like this first year's learning curve has been steep mechanically, and I spend as much time working on this bike as riding it.

Just wondering, would I be able to replace the front derailleur if it came to that to adjust for the different spindle length, as opposed to replacing the BB since it is new, and I'll probably need a new front Der anyway sometime in the not so distant future?
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Old 05-03-04, 10:59 AM   #9
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Originally Posted by franklen
Just wondering, would I be able to replace the front derailleur if it came to that to adjust for the different spindle length, as opposed to replacing the BB since it is new, and I'll probably need a new front Der anyway sometime in the not so distant future?
It's best to have the correct BB spindle length, otherwise you may encounter chainline issues...

Take another look at your F-derailleur's limit screws. Did you try detaching the cable from the derailleur to see if the cage completely swings from one end to the other with the limit screws completely out?
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