3alarmer

...would it be possible to post a photo or three of what you have there ? It is true (as has been mentioned already), that not all front derailleurs work well with all cranks and chainrings. (Or work at all, for that matter). Since it is an "inherited" project, maybe it was not well thought out to start with ? Anyway, my apologies for the current state of how threads in mechanics, asking for help with simple problems, all seem to degenerate into a stream of arguments. At this point, I would be reluctant to make any suggestions at all. But I also date back to the days when it was routine practice to bend the leading edge of the flat plates on front derailleur cages, to make them shift much better.

I'm just not really sure that bending will either work well in your case, or is even a good or bad idea.

I think I understand the issue to be: that the cage you have is pretty wide, so in order for the inner plate to contact and push the chain onto the large ring of your double crank, the whole cage ends up so far out that it interferes with the crank arm. I personally would not use bending in such a case. It might work, or it might not. It's possible that rather than flattening the derailleur cage as you are intending, you might get away with bending just the interior leading plate edge, inward, so it throws the chain sooner. Then your cage won't end up so for outboard as to interfere, and you can just use the limit screw to reduce throw. Hard to predict how well that might work.

Also, make sure you've got good alignment of the cage. Sometimes if the derailleur is a little cockeyed on the seat tube, either the front or rear of the cage will interfere with the crank.