Front derailleur drags on middle chainring?

[fionn88]

Hi guys -- I'm new to the forum. Thanks for reading.

I'm fixing up a bike I've had for ~15 years that, sadly, I wasn't able to maintain. The bike is an 18-speed Royce Union mountain bike. Aside from new tubes/tires and a new chain, everything else is original (thumb shifters, both derailleurs are Shimano).

The original chain was just too rusted, so I replaced it, and it runs nicely now. Almost. It's fine on the granny chainring, and it's fine on the big ring, but when it's on the middle ring (the one that I tend to use the most), the chain drags across the inside of the derailleur cage. Previously (when I had been maintaining this bike regularly before knee issues made riding a nightmare), I had had to adjust the low limit on the derailleur to keep it from dragging when it was on the granny ring, and it had been fine until I had to stop riding.

I'm planning on using this as a commuter bike for the next year or so, not for trails or long treks (not yet, anyway).

Any thoughts on what I can do to fix the chain drag on the middle chainring? Any suggestions/advice would be much appreciated!

[DaveM]

First thing to check is the alignment of the derailleur. The outside of the cage should be parallel to the chainrings and the bottom of the cage should just clear the top of the big chainring by 1-2 mm as it moves across.

If that's all set and nothing is bent/damaged, it would be normal that when you have the chain on the middle chainring and switch gears in the back, that the chain would start rubbing on the inside of the derailleur cage some. You would just need to adjust the derailleur a tiny bit to stop the rubbing.