Chain keeps coming off during front shift

[gavinb]

With no discernable pattern, i.e. gear ratios, pedal loading my chain keeps on coming off while shifting from the 53-tooth ring to the 39 ring. I am running Ultegra throughout and have a 12-25 on the rear.The front deraliar is adjusted so that is now just rubs the chain in the 39/25 ratio, still the problem continues. Every time the chain comes off is takes another gouge out of my Carbon frame and it’s pissing me off. Any ideas??

 

[Carrera]

I had a similar problem. The chain kept flying off when I released it from the big cog onto the smaller ring. Like yourself I got ****** off about it. It wasn't much fun to get my hands covered in oil while trying to get the chain back on the cogs.
My problem turned out to be badly adjusted gears and a worn bracket in my crank. Check to see if your crank is going round in an even circle. Is there any in out movement as the crank circles round? If so, you need a new bracket.
If your bracket is O.K. it has to be gear adjustment. Your bike has a number of screws you can turn to adjust the tension. If that doesn't work you can try altering the derailier, loosening it with an allen key and pushing it inwards or outwards.

With no discernable pattern, i.e. gear ratios, pedal loading my chain keeps on coming off while shifting from the 53-tooth ring to the 39 ring. I am running Ultegra throughout and have a 12-25 on the rear.The front deraliar is adjusted so that is now just rubs the chain in the 39/25 ratio, still the problem continues. Every time the chain comes off is takes another gouge out of my Carbon frame and it’s pissing me off. Any ideas??

 

[phroomters]

<--- sorry i dont really have much of a bikers vocab

This is after much stress altready working on the two screws that determine the range of your shifting capabilities

i fixed a similiar problem like that this morning where I had to bend the metal of the thing that feeds the chain into the chain ring. When I shifted the chain would just hop over the chain ring and fall off because the feeder thingy (sorry) was guiding my chain to the outside instead of keeping it inline even after i leveled it out, it was simply too wide of a range of guidence. modifcations were slight. be sure to that your chain wont rub your modified feeder when you shift in the back.

p.s. if anyone happens to know a web site that labels bike parts, i would be honored not to sound like i have no idea what im talking about

 

[daveornee]

With no discernable pattern, i.e. gear ratios, pedal loading my chain keeps on coming off while shifting from the 53-tooth ring to the 39 ring. I am running Ultegra throughout and have a 12-25 on the rear.The front deraliar is adjusted so that is now just rubs the chain in the 39/25 ratio, still the problem continues. Every time the chain comes off is takes another gouge out of my Carbon frame and it’s pissing me off. Any ideas??

It sounds like the stop is adjusted ok.
The height and angle are the other ajustments to be considered.
Take a look at those adjustments and instructions on Sheldon Brown's site:

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

The condition (including a possible tight link) wear and flexibility of the chain effect this.

You may find that the N-Gear JumpStop is required to keep this from ever happening. This device is one of the anti-derailment units that Sheldon refers to in his article.

 

[boudreaux]

If your bracket is O.K. it has to be gear adjustment. Your bike has a number of screws you can turn to adjust the tension. If that doesn't work you can try altering the derailier, loosening it with an allen key and pushing it inwards or outwards.

Mindless fiddling seldom gets it right. The repair section at www.parktool.com has the complete drill.

 

[Whitney]

You might check your chain length, as shown in the link above.

When you drop from the big to the little ring, you introduce quite a bit of slack into the chain which the rear Der. has to make up pretty quickly. You can get a little pop of the chain which can unseat it from the front ring.

If you try to simultaneously go down in front and up in the rear this can happen quite often, and if you have a chain that's a little long for the bike, then your rear Der. might not be up to the task of snapping it into line quickly enough.

This can happen regardless of the setting of the front Der.

Whit