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Old 04-02-08, 09:22 AM   #1
Macbike
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Chain falls between chainrings

I am fixing up a Trek 260 Mountain Track. Its about 15 years old, and has a triple chainring that is spot welded or something similar (as opposed to chainring bolts). Bottom line is that you can't take it apart. Rear is 6 speed. It was shifting poorly, I finally realized what the problem is: Spacing between chainrings seems more than normal. The chain actually drops between the teeth and gets stuck there before it gets a chance to properly engage on them. My theory is that the original chain(not on the bike now) might have been wider. I tried a new SRAM 6-7-8 chain, that was no help. Adjustments, lubrication, no change. Sometimes shifting occurs OK, but usually not.
Hope someone can help. The bike is for sale, and needs to function properly.

Thank you everyone,

Mike
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Old 04-02-08, 10:56 AM   #2
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Are you using indexed shifters? Does usually fall into one gap, or both equally?
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Old 04-02-08, 11:09 AM   #3
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Yes, the shifters are the twist grip kind, indexed.
There is more trouble going back and forth from the big ring to the middle ring. Little ring/Middle ring less problematic.
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Old 04-02-08, 11:16 AM   #4
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About the only thing I would suggest is buy the cheapest Wal Mart chain they have and hope it's "crummy" enough.
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Old 04-02-08, 11:21 AM   #5
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Could be a mis-adjusted FD.

Could be a worn crankset - the pins that pick up the chain on a shift have to be relatively sharp or the chain slips off. Got another crank you can try?
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Old 04-02-08, 11:27 AM   #6
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I adjusted the FD every which way before it dawned on me that the chain was simply falling between the rings. I don't have any spare parts other than chains. The bike is up for sale, I have a solid buyer, but not if it doesn't shift correctly. I'm going to contact Trek, maybe they can help.
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Old 04-02-08, 11:35 AM   #7
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On a 15 year old bike? Wishful thinking.

A chainring is a wear part like a tire and is supposed to be changed when worn out. There are inexpensive ones, btw.
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Old 04-03-08, 09:53 AM   #8
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Yup, go to LBS or local bike co op and get a used right crank with rings. Shoud be able to find one for $5-$10
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Old 04-06-08, 03:52 PM   #9
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Thanks to everyone for your ideas. The solution was a surprise: the chainrings are cheap stamped steel. Over time, what with shifting, stuck chains, and general abuse, the big ring was simply bent outward along its circumference. Several well placed blows with a dead blow hammer did the trick.
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