Chain dumping off small front ring

[Fifelad]

I had previous trouble with this and thought all was cured when after new front changer then new chain rings fitted and a dogtooth chain catcher fitted the problem was sorted then recently on the odd occasion the bloody thing has done it again arrghhhh ! I am thinking just a small tweak of the limit screw to stop the changer moving too far in and see how it goes. So much for the chain catcher doing its job.....it has happened when there has been a bit of tension on the chain at the foot of hills, but the chain has been in a straight line and not on a small ring at the back to when changing from big ring to small at the front ie no severe cross chaining. Not a good feeling not knowing when its going to happen and when I thought the problem had been sorted once and for all !

 

[Sittingduck]

As mentioned, adjust the limit screw. Tis what it's there for

 

[robgul]

+1 for the limit screw .... but, which way is the front mech sprung? (i.e. the default position before you connect the cable) - if it's to the smallest ring then the cable may be slack ... I have found that a little bit of tension on the cable even when the mech is at the default and stopped on the limit screw is better ... and reduces the risk of the chain unshipping.

I assume the chain is the correct length for chainring/cassette combo?

Rob

 

[derrick]

Tweak the limit screw.

 

[cyberknight]

Is your front mech to high or twisted ?
I used to have the same issue till i lowered the height of it

 

[Fifelad]

Thanks for the input troops

 

[migrantwing]

As @cyberknight said, drop that mech down as low as it will go without touching the chainring teeth. Shifting will be sweeter, too.

 

[Globalti]

Tweaking the stop screw and messing with the cage height won't cure it; the problem is that some front derailleurs clack across so fast that they simply throw the chain off. I'm surprised the dog tooth thingy isn't preventing it. I had this problem a lot when I got my first decent road bike and after some embarrassing "offs" when the chain came off at the foot of a climb I fitted a K-Edge chain catcher, which sorted it out. I now always fit one to my bikes.

 

[shouldbeinbed]

I'm another vote for tweaking the mech height & position before adding aftermarket catchers, better to exhaust every possibility to mend the problem than simply mitigate it.

 

[cyberknight]

If your mech is adjusted correctly you shouldn't need a chain catcher, sure they are nice as a back up for when shifting under load ( ask Andy Schleck ) but not every day, i dont have them on any of mine and i dont have issues.