chain grinding on derailleur

bikeguy said:

Hello,

I'm riding a Nishiki sora road bike and I'm having a problem with my chain grinding on the front derailleur. The only way I can stop it is by pulling the big ring shifter and even then it grinds sometimes. Any way I can fix this problem? I've also noticed the bike flexes quite a bit when I really put the pressure on the pedals, and I think this is what is causing the grinding. This bike has an aero down tube, buts it's so weak and flexy that the whole bottom bracket moves when I apply a lot of power. I think the grinding is eating up quite a bit of power. If I can't fix this problem, I'll get a new bike (Giant, Kuota (used) or Cannondale).

-Bikeguy

Are you crosschaining?

I have an Allez Sport and have noticed that it flexes quite a bit too. I've only noticed it when I'm using a trainer as I don't look down at my BB when I'm riding on the road. The only time the chain rubs against the F Der is when I've crosschained it. I either adjust the trim or change gearing to alleviate the problem. If you really want a new bike though, neither of those are recommended solutions. 😉

Edit: Try googling or doing a search on this forum for some information on gear inches to see which gears are similar in the big and small ring. There was a thread here recently that went into detail but I don't remember which one.

From what you say, it sounds like simple derailleur mis-adjustment.

IF it ONLY happens when you're applying FULL power (standing up and hammering uphill), then I could see your frame flexing enough to dramatically effect chainline.

Otherwise, I'd just go back to the basics with your front derailleur adjustments--primarily your upper limit screw.

http://www.parktool.com/repair_help/howfix_frontderailleur.shtml

http://sheldonbrown.com/derailer-adjustment.html#front

Thanks for the links neil0502, I don't know anything about how to adjust derailleurs. About the rubbing, I can get it to rub for over 30 minutes, the lower gear I go in, the less flex, the less it grinds. The grinding coincides with when the crank is parallel to the ground. It grinds big time when I'm in the big ring and like a 14-13 or 12 rear. It grinds less in the small ring, but still there when I move up to 14-13-12 rear. Will try adjusting it.

-Bikeguy

bikeguy said:

Thanks for the links neil0502, I don't know anything about how to adjust derailleurs. About the rubbing, I can get it to rub for over 30 minutes, the lower gear I go in, the less flex, the less it grinds. The grinding coincides with when the crank is parallel to the ground. It grinds big time when I'm in the big ring and like a 14-13 or 12 rear. It grinds less in the small ring, but still there when I move up to 14-13-12 rear. Will try adjusting it.

-Bikeguy

if you go to the shimano web page you should be able to down load the adjustment instructions / diagrams that the stuff is sold with , one thing is your frame may be bending but that´s not the cause of the problem unless your name´s Hinchcapie or Zabel .

The problem is almost inevitable so the best option is to choose which is your least used gear where some grinding won't trouble you. Here is the way I do it:
Ride your bike and change into the particular gear that grinds the most. Dismount. Adjust your derailier so the gap between the chain and the derailier increases and clears a space. Make sure, however, that the shifter still moves your chain over onto the big crank.
More than likely, you'll find that this adjustment will transfer the problem to another gear on an outermost cog. Unfortunately my very low gears presently grind but I know I can shift the problem to less used (bigger gears).

bikeguy said:

Hello,

I'm riding a Nishiki sora road bike and I'm having a problem with my chain grinding on the front derailleur. The only way I can stop it is by pulling the big ring shifter and even then it grinds sometimes. Any way I can fix this problem? I've also noticed the bike flexes quite a bit when I really put the pressure on the pedals, and I think this is what is causing the grinding. This bike has an aero down tube, buts it's so weak and flexy that the whole bottom bracket moves when I apply a lot of power. I think the grinding is eating up quite a bit of power. If I can't fix this problem, I'll get a new bike (Giant, Kuota (used) or Cannondale).

-Bikeguy

bikeguy said:

Hello,

I'm riding a Nishiki sora road bike and I'm having a problem with my chain grinding on the front derailleur. The only way I can stop it is by pulling the big ring shifter and even then it grinds sometimes. Any way I can fix this problem? I've also noticed the bike flexes quite a bit when I really put the pressure on the pedals, and I think this is what is causing the grinding. This bike has an aero down tube, buts it's so weak and flexy that the whole bottom bracket moves when I apply a lot of power. I think the grinding is eating up quite a bit of power. If I can't fix this problem, I'll get a new bike (Giant, Kuota (used) or Cannondale).

-Bikeguy

I had the same problem today.

Went out for a 4 hour spin earlier and for the first hour had to adjust the top
screw several times to completely stop that rubbing sound.

Got to the derailleur mech and you will see two small screws at the top of the mech.
Adjust the upper screw (as you do so you should see the derailleur move).
This should stop the grinding of chain on derailleur guard.

This reminds me of one aspect of friction shifter that I liked. You could adjust the front derailer position on the fly and never experience that annoying grinding noise.

Thanks guys, I played around with the 2 screws and I got it to stop grinding on the big gears which I use a lot. I really have no need of the small chainring.

I have noticed though that I can't back pedal without the chain going slack and popping off. What kind of problem do I have here?

-Bikeguy