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Old 02-27-14, 10:42 PM   #1
Isaiahc72
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Chain going off large chainring?

I had my chain go off my largest front chainring the other night but was able to down shift and get it back on before it got out of control. However I haven't adjusted my limit screw since and also haven't had any issues like that. So I'm wondering, is it normal for this to happen every once-in-a-while? Or should I really try and restrict my limit screw adjustment to be closer to the chain?
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Old 02-27-14, 11:20 PM   #2
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It isn't normal for the chain to overshift off the large chainring, if that is what happened. I would check front derailleur adjustment. Park Tools website or Sheldon Brown website have procedures for this.
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Old 02-27-14, 11:48 PM   #3
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Quote:
Originally Posted by jyl View Post
it isn't normal for the chain to overshift off the large chainring, if that is what happened. I would check front derailleur adjustment. Park tools website or sheldon brown website have procedures for this.
^^^this^^^
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Old 02-27-14, 11:54 PM   #4
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With the bike on the stand, use your left shifter (FD) and try to move the chain off the right side of the large ring. If you can, it needs adjustment. With most FDs, the adjustment is an eighth to a quarter turn clockwise on the screw closest to the rings. Check chain wear first. Best.
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Old 02-28-14, 08:16 AM   #5
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Tiny adjustments to the limit screws (1/8 turn or so at a time ) should fix the problem. Agree, it's not normal or acceptable.
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Old 02-28-14, 08:48 AM   #6
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It can be a little bit more complicated if you have indexed shifting.

If the front derailleur is a "high normal" type (the derailleur heads toward the big ring when the cable is slack, these are less common) then you adjust the high limit screw first so that you can just get cleanly onto the big ring, then the cable tension so that the shifts to the smaller rings work smoothly.

If the front derailleur is "low normal" (the derailleur heads towards the small ring when the cable is slack, most common) then you adjust the cable tension first so that you can just get cleanly onto the big ring, then the high limit screw, leaving a slight bit of room for overshifting. If you get the high limit screw too tight, it can interfere with shifting because the derailleur may need to move a tiny bit outward past the ideal position before moving inward (depending on the design of your shifters, some pull on the cable a bit extra to clear pawls internally, then let it settle back.)

Either way, you may need to go a few passes between cable tension and limit screws.

Of course, none of the above applies with friction shifting. Set your limit screws so you don't dump the chain off, and go ride.
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Old 02-28-14, 08:51 AM   #7
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If you are in one of the smaller cogs in back, it might be a bit more likely to overshift off the front ring because the chains is already outboard. Whereas if you are on a larger cog in back the chain is inboard and slightly more resistant to being overshifted. When adjusting the front, I usually check that it works both directions in combination with different gears in back.
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