Bicycle Mechanics - Rear derailer chain rub

I'm running a 1 x 7 setup, with a 46-tooth chain ring. When the RD is lowest gear (28-tooth), the chain rubs on the jockey wheel cage. It shifts fine otherwise and doesn't seem to have any problem in any of the other gears. Any ideas? Thanks.

Looks to me like your chain is at least 4" too short, maybe even 5". RD should NOT be straightened
out like it is in the pix. www.parktool.com and look under the repair button top right and under RD
adjustment for pix of the proper alignment.

Wow... even a noob like me knows that RD is not a happy camper. Disintegration in 5...4...3...2...1... KABOOM!

"KABOOM" might not be the worst fate for a Shimano Tourney - but aside from such - the Tourney does require more chain. If that's a pretty new cassette, get another chain for the bike. And don't start pulling links until you know what you're looking at.

Well, the instructions that came with the derailer said to wrap the chain around the largest front chainring and largest rear sprocket and add two links, which is what I did. The Park Tool book says to add one link, iirc. Sheldon says something similar.

Here's a picture of the derailer with the chain on the smallest cog, for the sake of comparison. The chain is new, so if I add links, can I just add those I took off originally?

It looks to me as if you need to add one or maybe two links.
A link of chain is one inch, includes both inside plates and outside plates.
You need to use the special Shimano link pin when joining chain. Do not reuse the old pins that were removed from the chain.

Al

I might back off from my original 4"-5" recommendation but you need at least 2", maybe 3"
more chain. Your second pix shows the RD cage about where it ought to be for the middle
of the cassette, not the smallest cog. You can reattach the the removed links, likely safely
with a chain tool, or with an appropriate master link or the shimano pins as per AL.

I was having problems with the master link on my chain, so I bought a new Shimano 6-7-8 speed chain (116 links) and installed it. I didn't take any links out. If this looks OK (smallest cog left, largest cog right), then you were right with the 4 or 5 inches. I think this is about 4 links longer.

Here's a picture of the derailer with the chain on the smallest cog, for the sake of comparison. The chain is new, so if I add links, can I just add those I took off originally?

Yes. But there's a bit of finesse to not getting tight links.

Approximate rule of thumb. Put the chain on the Big-Big cog & sproket. The derailleur pulleys should be about 45 degrees to the ground.