Krov9

So I just bought an old Suntour Vx set for € 30, mainly for the RD. I might want to use the FD too, but the chain has done some pretty nasty looking damage on it (see pic).

What do you think could and should be done here? Should I sand it smooth? Try to find a replacement? Discard it? Use it as is? Thanks for helping out a novice

Iride01 

You can do any of those things that make you comfortable. I wouldn't even bother trying to sand it smooth. I'd just put it on and use it until it gives me a real reason to not use it.

If it lasts you one season or twenty more riding seasons, then you saved that much wear and tear on the part you'd replace it with.

With the chain and everything else in place, someone will have to look hard to see that little bit of ugliness. Likely that will only be you.

Crankycrank

+1 with what Iride01 said. Try it first as is and if it works fine just leave it as is. If you find the chain is getting hung up on the cage then sand the cage smooth. If that doesn't work it's time for a new derailleur.

dsbrantjr

if it works leave it be. Never Fix A Running Piece.

Iride01 

One more thought though. And purely speculation, but the excessive wear may have been from the DR not being parallel to the chain and it was leading with the nose whenever it shifted up to the bigger ring. Is there perhaps a little more indication of wear toward the tail end of the outer cage plate?

dsbrantjr

Or by being poorly adjusted and ridden with the chain rubbing over an extended period.

Krov9

This is my best guess how it ended up that way. I have my eyes on a replacement that could be had for less than 10 €, but I think I'll give this a try first, as suggested. I'm not that experienced in (working with) derailleurs, having ridden IGH bikes most of my life.