Chain jumping off lower pulley

[Mike_P]

Had what I thought was a stretched cable to the rear derailleur but after much fiddling could not get the irregular noise of the chain slipping on a cog to go away and then, with the bike upside down, spotted the chain running on the side of the lower pulley. Is that pulley unduly worn?

The derailleur was new earlier this year.

 

[fossyant]

Yes, the jockey needs replacing, but why - I think your cage might be bent or the drop out - not seen wear like that before.

 

[Mike_P]

Looks like another new derailleur

 

[fossyant]

PS the lower jockey isn't stiff ? Or the chain not lubed.

 

[fossyant]

Looks like another new derailleur

Post a picture with the bike upright, but take a picture from low down from behind the bike. The mech cage should be parallel to the wheel.

 

[fossyant]

PS don't ever diagnose problems with a bike upside down (hate folk doing this even wheel changes), or turning the pedals the wrong way. Your bike doesn't work like that, and you'll get ghost shifts. You could get new jockeys for a tenner.

 

[Ming the Merciless]

Teeth don’t look unruly worn. They’d be sharks teeth if so. Sometimes a chain can jump off The lower if you hit a bumpy bit and the derailleur doesn’t hold the tension well enough. More common on mtn bikes but roads are getting tougher. Put chain back on lower wheel and see how you get on.

 

[Darius_Jedburgh]

PS don't ever diagnose problems with a bike upside down (hate folk doing this even wheel changes), or turning the pedals the wrong way. Your bike doesn't work like that, and you'll get ghost shifts. You could get new jockeys for a tenner.

Exactly. It always surprises me that problems can be diagnosed with the bike in an unnatural position.

Teeth don’t look unruly worn. They’d be sharks teeth if so. Sometimes a chain can jump off The lower if you hit a bumpy bit and the derailleur doesn’t hold the tension well enough. More common on mtn bikes but roads are getting tougher. Put chain back on lower wheel and see how you get on.

My thoughts too. Seem to be plenty of life in those wheels. They can be almost worn away and still work.

Not enough info to diagnose accurately.

 

[fossyant]

The lower jockey doesn't look right - might have been stiff as the teeth should look like the top jockey.

 

[Mike_P]

Does this help

It is a Shimano 11 speed and the wheels do differ i.e.

 

[Darius_Jedburgh]

Agreed the teeth are more worn, but not worn enough to cause problems.
So what else is going on? Photos are little use.

 

[Darius_Jedburgh]

Does this help
View attachment 532426
It is a Shimano 11 speed and the wheels do differ i.e. View attachment 532428

Not really. We cannot see what is going on with the deraillieur. Too dark and the wrong angle.

 

[Ming the Merciless]

This is what worn wheels look like. Even these weren’t really shifting badly. New ones are running smoother.

 

[Ajax Bay]

Keep those jockey wheels out of the 'blame game'. Both the wheels in the OP image are fine (see first one below).
When they wear they go 'ninja' (images 2 and 3 below ).
The dark and difficult to see image shows the chain 'cross-chained' largest sprocket to large chainring (I reckon). The tension jockey wheel has a job to do, more so when cross-chaining. And I agree with @fossyant's 'deal with the bike the right way up' plea.

the irregular noise of the chain slipping on a cog

How irregular? Or is it regular? How do you know that the irregular noise is "the chain slipping on a cog"?
Can you hear it on all sprockets or just one? Does which chainring make a difference? Can you hear when applying power (ie up hill or starting)?

 

[Mike_P]

The chain was on the smallest chainring, it was lubed on the 16th (Fenwick's Professional) and has since done 106 miles, 6243ft up. The reason for flipping the bike was to tighten the cable bolt using an Allen key bit in a screwdriver and that's when I spotted the chain off the wheel. Another photo;

Think the cage is bent