Chain jumping off

[Moby Jones]

Can anyone help me out with this problem. My bike is only about 3 months old but within the past two weeks the chain has came off three times now. It only seems to happen when i wish to change from the large sprocket to the small sprocket.
I recently lubed my chain could this be the problem, i did remove the excess lube from the chain by using a rag to give the chain a good wipe?????/

 

[Herzog]

As the bike is new, it could be your cables stretching (this is perfectly normal). You can tighten them up a bit, and adjust your limit screw so the the front derailleur cannot shift the chain too far.

 

[amaferanga]

I guess you mean chainrings as opposed to sprockets? The ones at the front....

If shifting is ok then there's probably no need to adjust cable tension. But it sounds like you do need to adjust the limit screw so the front mech doesn't move in as far when you change from big to small. If you adjust the limit screw eventually you will reach a point where the chain won't shift from big to small - once you reach this point then back it off a little and you should get a smooth shift still, but the chain shouldn't overshoot the small ring when you shift down.

 

[Angelfishsolo]

Agreed.

I guess you mean chainrings as opposed to sprockets? The ones at the front....

If shifting is ok then there's probably no need to adjust cable tension. But it sounds like you do need to adjust the limit screw so the front mech doesn't move in as far when you change from big to small. If you adjust the limit screw eventually you will reach a point where the chain won't shift from big to small - once you reach this point then back it off a little and you should get a smooth shift still, but the chain shouldn't overshoot the small ring when you shift down.

 

[Moby Jones]

Sounds like good advice, i will give it a go. Thanks

 

[Jimmy Doug]

Limit screw problem, almost certainly. The thing is, when you make that little adjustment, you really need to ride it afterwards and check it out. Some bicycle shops don't do this. They put the bike together, put the bike on the stand and make the adjustments from there. Then, you take the bike out and find that the adjustments aren't quite correct. A common problem.