Why does my chain keep falling off?

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elg's picture
elg
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Joined: 22 Jul 2009

My new sofrider has an odd problem. The chain keeps falling off of the front sprocket. Mine is an 8 speed, so there is no front derailleur, (which at least makes it easier to put the chain back on).

I've had the bike for about a week, and on every ride I've taken the chain has fallen off at least once. It seems to be tied in with shifting, but I've got the wheel cluster derailleur adjusted so that it shifts perfectly.

What could be the problem? Is the spring on the tensioning arm adjusted wrong or too weak? Short of tossing out the gearing and installing an internal geared hub, what can be done to fix it? Any advice would be appreciated.

John Zabriskie's picture
John Zabriskie
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Joined: 16 Nov 2009
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Re: Why does my chain keep falling off?

Ed,

Check for a bent tooth or two on the chainring (while the chain is off). They should all be in line & not twisted or offset. A straightedge across a group of teeth will give you a good idea if all are straight or not.

Doug Burton's picture
Doug Burton
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Joined: 1 Mar 2008
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Re: Why does my chain keep falling off?

Ed,

You might also run the "B tension screw" in a bit and try it. These chains err on the long side for length, and the combination of slack B-tension, plus long chain, plus a bump or something that gets the chain bouncing a little, can derail it.

http://www.sheldonbrown.com/derailer-adjustment.html

Best,

Doug

elg's picture
elg
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Joined: 22 Jul 2009
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Re: Why does my chain keep falling off?

John and Doug,

Thank you for the advice. I checked for tooth alignment on the sprocket and found no problem, so I tightened up the tension per the link in Doug's message. Time will tell, but I didn't drop the chain during my ride to work this AM.

Ed

Gromit's picture
Gromit
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Joined: 6 Mar 2008
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Re: Why does my chain keep falling off?

I wonder if an N-Gear Jump Stop would help to keep the chain on the chainwheel?