Chain Dumping off small front chainring

[Fifelad]

Going demented, changing beautifully through the gears but for every 20 times its ok boom it dumps off the front ring ,especially under tension. Usual checks low/high limit screws set fine.Took into the LBS and they have checked my own efforts at tuning the gears, everything ok, they have even checked the frame, a new front changer fitted also. The LBS mechanic did notice that the REAR mech hanger was a bit off so sraightened it. Worked a treat until nearly back at the house and off it went again. The rear mech is worn and needs changed anyway.I am assuming the if the rear mech is a bit off it could affect the changing at the front? only other thing I can think off is that the front chain rings could be replaced although they are not that bad and should have a bit of life left in them yet.Has anyone had a similiar scenario ? opinions please

 

[Spoked Wheels]

The limit screw is the only thing I can think of really. So I'm curious to learn what it is if it turns out to be something else

 

[Cycleops]

If you've changed the front derailleur and adjusted it it can't be that, so must be the rear one, unless the chain is too loose or the chain wheel is warped.

 

[Crackle]

Sometimes the angle and height will cause it to drop the chain. Experimentation might be needed and yeah. ^ dog fang as well.

 

[Roadrider48]

Slightly bent rear mech hanger?

 

[Svendo]

Worn chainring, sometimes not holding onto chain well enough as it drops?
But I'd also recommend the dog fang, or if the seat tube is not round/too big/delicate carbon then a 'blade' style chain catcher.
But good luck, I find FD adjustment a proper dark art, and have to go back to the start with any adjustments. RDs I can usually work out what small adjustment is needed but with FDs I have to get the tech doc out and start from scratch. Doesn't help when the last time I tried I had the wrong tech doc, and the limit screws had swapped positions between shimano 4400 and 4500, which was confusing until I checked the actual derailleur model number.

 

[Nigelnaturist]

Wouldn't think the RD will effect it much as the chain is at the top when its shifted not the bottom like the rear, I would suggest worn ring, I get the very odd off on the large which i think is probably front rear gear combo.

 

[Fifelad]

Thanks for the input folks

 

[Gravity Aided]

Or the twist shifter could be giving you problems.I'm figuring the LBS would have caught that, or misalignment of FD. Dog fang may solve all woes.

 

[Fifelad]

I'm alien to dog fang prey tell.....

 

[cyberknight]

I'm alien to dog fang prey tell.....

aka chain catcher, stops the chain falling off the lower chain ring

 

[derrick]

Dog fang will not stop it dropping off.

 

[mrbikerboy73]

I had the same going from small to large, worn chain and front ring were the culprits.

 

[Racing roadkill]

It's all about the rotational speed of the cranks when you change up / down. If you use Di2 / EPS, it's all taken care of, but with mechanical shift, you have to make sure you back off on the front downshift, or speed up before the front up shift, other wise you risk an embarrassing dechaining.

 

[Fifelad]

Thanks for the input folks I hear you roadkill and I do apply the principles you have described but it should not be happening on my other bike for example, granted with a much higher spec in ultega it does not happen at all even if one forgets where the chain is positioned