Problem with new setup
Hello, I have upgraded by myself my road bike from Sora to 105, except for the chain and the sprocket, both DA. All is working well, but the sprocket in the smallest cog rubs against the second smallest or goes against the drops, up to how I adjust the smallest top rear derailleur screw. It's a 50/34 crankset with a 11/28 sprocket. Also when I start pedalling in that smallest cog the two or three first pedal wheels the chain wants to go to the second smallest, but it returns to the smallest, and all the way it's rubbing and noising. I think perhaps the chain is too long or too short, or the rear derailleur is bent, or the B-tension derailleur screw it's not properly adjusted, but when I tight or untight this screw nothing happens, I haven't tighten it at most but until half the way nothing happens. I have thought also if there has to be some spacer between the 2nd smallest and the smallest cog. Is there any solution? If the chain is too short is it easy to add some link? Many many thanks and sorry for my english.