Dumb gear question

[swee'pea99]

I'm embarrassed to ask - I've been maintaining all my own bikes for decades - but I'm stumped by what is I'm sure a very basic & obvious problem.

I fitted a new derailleur to my daughter's bike. She tells me she got about a mile before 'there were some horrible sort of grindy noises and it sort of jammed up', since when she's been riding it single speed.

Obviously something is horribly wrong with the gear setup. In big front & rear, it almost doesn't look ridiculous:

But on anything else, the mech starts folding back, until on small front + small rear it ends up at:

I feel like I need to take 8" out of the chain before it even begins to make sense, but that can't be the answer.

What have I done wrong?

Thanks in anticipation for any help/suggestions.

 

[DCLane]

It looks like the chain is only threaded round the bottom derailleur jockey wheel, when it should be round the top, then the bottom.

 

[raleighnut]

It looks like the chain is only threaded round the bottom derailleur jockey wheel, when it should be round the top, then the bottom.

Nah you can see it over the top jockey.

As for the set up. well I don't think the rear mech has the required capacity (needs to be a 'GS' version) and the chain is too long.

 

[Sea of vapours]

Is the mech in the right position on the mech hanger? I don't know what that mech is, so don't know what it should look like, but it could be that the 'top' part of the mech should be about 90 degrees further back / clockwise. Failing that, it's lack of mech capacity as well as a substantially over-long chain.
EDIT: I meant to say that there is a lug on the top bit of the mech, sitting at about 3 o'clock in the top image, which has moved in the lower image. Is there nothing on the mech hanger which that lug can sit against, keeping the top bit of the mech further clockwise when under tension?

 

[swee'pea99]

Thanks for all your replies. Yes, the route the chain takes is fine. It's something to do with the mech and/or the way it's mounted on the frame.

I'm pretty sure the mech is correctly positioned on the hanger:

The screw/lug says to me that has to be right.

Whether the hanger is correctly mounted on the frame....?

But even some not-quite-rightness there surely wouldn't account for that amount of slack?

Proper baffled, me. Thanks again. I'm stopping for tonight, it's doing my head in and the light is at last beginning to fail.

Happy solstice!