Another Chain Falling Off Problem

[JtB]

I've recently had a new chain, cassette and chain set fitted (although I didn't do the chain set myself). Since then the chain has fallen off several times (and jammed between the small chain ring and the frame), each time on changing down to the small chain ring. After it fell off the first time I adjusted one of the front dérailleur limit screws so the dérailleur moves just far enough to the left so as not to rub on the chain when the chain is on the small chain ring and largest rear sprocket. So I can't limit the front dérailleur movement any more otherwise it will rub on the chain, and yet the chain has still fallen off several times since.

The first time this happened I was on a hill climb and changing up through the rear gears (although not to the smallest sprocket) whilst at the same time changing down to the small chain ring. I've subsequently been able to reproduce this several times by gently pedalling along the flat and changing down to the small chain ring while the chain on the smallest rear sprocket.

Any ideas anyone?

 

[13 rider]

Chain catcher is the easiest fix . I used to have issues on my hybrid chain coming off between frame and chain rings fitted a dog fang chain catcher cheap easy to fit no more issues

 

[GlenBen]

Agree with the chaincatcher.

Was the chainset the same? Did it require a different sized bb axle?

 

[boydj]

Best to go up through the rear cogs to about half-way before dropping to the small ring. Switching rings with the chain at either extremity at the rear is much less reliable.

 

[Psycolist]

Best practice, so I am told, is that the outer chain ring on a triple should be used on the smallest rear cogs, the middle chain ring on the middle rings of the cassette and the inner chain ring only used with the larger rear cogs. Its all about the chain line, putting the chain on the opposite extremes at both end causes excessive chain wear and problems such as you describe. However, if it was all working OK before changing the chain set, I would check that the new chain set has been tightened onto your bottom bracket properly. If it has, then I reckon there is a miss match of bottom bracket and chain set.

 

[Ajax Bay]

putting the chain on the opposite extremes at both end causes excessive chain wear and problems such as you describe

While I agree with your best practice, I don't think cross chaining causes the problem the OP describes.
I winced reading "by gently pedalling along the flat and changing down to the small chain ring while the chain on the smallest rear sprocket". Seems like a limit screw issue to me. I'd be prepared to put up with a bit of rubbing in LOW gear if that meant my chain didn't fall off. Also technique (reiterating/reinterpreting what @boydj said): change down to small chainwheel later (and not under (climbing) load) ie change up (ie to bigger sprockets) on the cassette BEFORE changing at the front. If you need to do a double change, do it in the middle of the cassette.

 

[JtB]

The front mech is bent and seems worn since there's quite a bit of movement. Also, my gear changing technique was lacking, so from now on I'll be changing to the small chain ring while still on a large sprocket, then changing to a smaller sprocket after the chain has moved to the small chain ring. Many thanks all for the comments and education - lesson learnt.

 

[Ajax Bay]

gear changing technique . . . from now on I'll be changing to the small chain ring while still on a large sprocket, then changing to a smaller sprocket after the chain has moved to the small chain ring.

Sorry that my post was not clearer, but this is not what I recommend. Anticipate what gear you're going to need ahead and in the middle of the cassette (ie after having moved up/down the cassette) change to the smaller/larger chainring so that the range of gears you'll need a few hundred metres ahead is the best option. To avoid a large gear ratio jump, you may need to 'double change' if you have a compact (50-34): as you change to the small chainring, click down the cassette one or two to a smaller sprocket. And vice versa, as you change to the large chainring, click up the cassette one or two to a larger sprocket.