# chain falls off front big ring



## blantonator (Apr 25, 2007)

I just put a new FD and my chain comes off every once in a while, what did i do wrong?


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## amicus (Mar 2, 2007)

blantonator said:


> I just put a new FD and my chain comes off every once in a while, what did i do wrong?


You need to adjust the limit screws on the derailleur


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## superflychief (Mar 25, 2008)

Depends which way it's falling off. If it's falling off the towards the bike, you need to adjust your barrel adjuster counter clockwise (effectively lengthening the housing) till it stays put. If the chain falls off the ring towards the outside of the bike then you need to adjust the outer limit screw. It's the screw on the FD that's labeled "H". If they aren't labeled then just tighten one or the other to learn which way they move the derailleur. When you tighten the high limit screw it shortens the derailleurs path not allowing it to go too far past the big ring. Basically you have to tighten the screw till you just have no rub between the cage and the chain in the big front ring and small ring in the back. Problem solved. Check out Park Tools website. They have a great tech section that explains virtually every part on a bike.


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## pgk (Jun 30, 2008)

Here ya go.

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


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## gnatman (Jan 14, 2009)

After setting the limit screws as described above, also check that the front detrailuer is aligned with the chainrings.


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## FBinNY (Jan 24, 2009)

gnatman said:


> After setting the limit screws as described above, also check that the front detrailuer is aligned with the chainrings.


*Check the alignment first*, since you'll have to re-adjust the limit and trim settings after moving the FD.


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## frmrench (Apr 10, 2009)

FBinNY said:


> *Check the alignment first*, since you'll have to re-adjust the limit and trim settings after moving the FD.


And as a rule, I always set my FD cages so they're ever so slightly towed-in. Almost parallel with the chainrings, but not precisely so.


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