Front derailleur tuning issue: chain drops when shifting to largest cog, but is very difficult to shift into largest cog and when limit screw is pushed back in even 1/4 turn chain doesnt go up at all (more pics and info in comments)

https://preview.redd.it/17r5jyd1drgd1.jpeg?width=2268&format=pjpg&auto=webp&s=719626031a08d53b85f8c0dfeb05108f23dd1bca

Front derailleur height

The tooth step is 42-53, the FD is older Suntour and scavenged along with chainrings, though appear to be in good shape. The chain is 10 speed. Derailleurs are operated by friction shifters. When operating it takes an extremely long time for the chain to catch, and if it catches at all 50% chance it drops. Opening the limit screw pretty much guarantees a drop, and closing the limit screw doesnt push the chain far enough at all. Is there a parts compatibility issue or is the setup wrong?

It sure looks like your middle chainring is on backwards. Those are usually beveled and if it is on wrong then it will increase the distance between your middle and large rings, resulting in poor gear changes.

You also need to align your rings. There’s a single nub on the inside of each ring. On your middle it seems to be in the 8 or 9 o’clock position. On the small ring it is more like 2 o’clock. I can’t see what’s happening with the big ring from that photo. The big ring should determine everything as that has the chain catching pin which hides behind the crank. The ring may also have a nub. Line the middle and small rings up with that. And if there’s no nub on the larger ring, then at least get the middle and small aligned.

I agree with the other poster about derailleur alignment. The inside cage is usually the parallel on one older derailleurs and that needs to align with the chainrings. Also, those older derailleurs have a lot of flex and that doesn’t translate into good shifting.

Then there’s your large ring which doesn’t seem to have much for pins and ramps. I’m just going by slow motion in your video to conclude that. Modern chainrings usually have at least four sets of pins and ramps to help the chain climb.

So you’ve got some optimizing to do, but should all work. Parts bin drivetrains are always a challenge to troubleshoot.

The hard to shift is because you’ve clamped the cable incorrectly. You need the cable to go up and over the little tab like this: [https://i.sstatic.net/H2TNb.png](https://i.sstatic.net/H2TNb.png) It looks like you’re going under the little tab.