Front derailleur at limit, but still heavy chain rub on cage

Question

Back story: I bought a Giant Defy Advanced Pro 2 second-hand, with Shimano Ultegra components. The previous owner had used it with different components and had the original ones re-assembled before selling.

In lower gears (up to ~4th one in the back), the chain rubs on the front derailleur cage. In the lowest one, the rubbing is quite extreme.

After I failed to configure the system in a way that would avoid rubbing, I took the bike to a shop. The mechanic there told me that the cage appears to be too far from the frame, so it's not possible to avoid chain rub, but couldn't explain why this could happen (especially given components are original). Allegedly there's not too much one could do differently with the given parts.

What could be the issue here - is it possible that in fact something was mounted incorrectly, or that some custom parts were used? Any ideas how to mitigate the situation?

Update: Here's a different view on the front derailleur cage; I'll post more once I get home.

Update 2: After some hints, I started testing around by pushing the cage by hand and felt it hitting a "limit" that was not caused by the L screw. Turns out that there were two reasons:

1. The tension screw gets in the way if it's not fully in, so I put it all the way in.

2. The H screw somehow limits the movement on the lower side if it's in too deep. Screwing it back a bit allowed me to go low enough to avoid chain rub on the low side. However, now there's significant rub on the high side, because I had to move the H screw!

I'm starting to wonder whether tension on the wire is too low, although tension adjustment itself is difficult because of the screw touching other parts as above. Trying to tighten it a bit yesterday had no effect, but I think I failed to actually put enough tension - putting the wire into the holding with tension felt very fiddly, and fine-adjustment only goes so far.

As asked by Criggie, here's a side view as well:

Still happy to hear suggestions what could be wrong with my setup!

Answer 1

I have the impression that it is a low limit screw issue, but am surprised that the bike shop didn't think about it if it is the origin of the problem (it is one of the first adjustments to make when installing a front derailleur).

The picture shows the front derailleur on my bike (a GRX, but same design as the Ultegra): you can see that your cage doesn't as far inwards compared to the one on the picture. I circled in red the limit screw of the derailleur, that seems much further on your pictures (second one).

The limit screws are located here - the one you need to adjust is the L one:

Source

Answer 2

After some back and forth, the issue turned out to be related to lack of tension on the cable.

To increase tension, I put the derailleur into a position near the "trim position" (one click below top, see Shimano's manual). To keep it in place while I was attaching the wire, I simply clamped some object of appropriate size between the frame and the cage.

Before re-attaching the cable, I partially released the tension screw, so I could fine-tune and add more tension later.

After the cable was in place with more tension, I was finally able to set up positions with the L and H screws in a satisfactory-enough way. There is a tiny bit of chain rub left in lowest and highest configurations, but that's probably not a big deal.

I noticed that moving the limits further out would cause more chain rub on the other side, i.e. high front with lower back gears and vice versa. This is of course expected to some degree, but it seems more of a problem than what I've seen on other bikes. But that's a question for another day.

Answer 3

Unfortunately I don't have enough reputation to make a comment so I should probably not be proposing an answer :D

There might spacers between the chain ring and the chain guard (although this is an unlikely from the comments below). Perhaps those spacers were misplaced, displacing your chainring.

Update: this might be a dumb idea, but have you checked that cables are not rusted or blocked, thus preventing the derailer from coming all the way down?

Hope this helps!