Removing bike rust on rear cogs?
 

Is it possible to remove bike rust on the rear cog of my mountain bike? I've been looking around but can't seem to find anything about the rear cog. This is for aesthetic purposes, I'm trying to make it look nice. The bike is about 1.5 months old.

Yeah, it's possible. Why is it rusty? Are you running your chain dry (i.e. un-lubricated)?

If the bike has 8-9spd rear cluster, then you can easily disassemble the cluster and clean the cogs off
with degreaser and some nylon abrasive pads which should take care of the rust as well. If the cogs
are rusty then the chain is even more likely to be so. Flash rust goes away with a bit of lube and
riding. If the bike is 6-7spd it may have a freewheel, not easily taken apart. Just clean, lube and
ride it.

Simple. Oil the chain and ride the bike.

Unfortunately, and I left it in the heavy rain this past month to top it off.

Yes the free wheel does not have a removable pulley or anything. But, you are saying just lube it and it will come off is that corrrect? Do you have a list of things I need to buy? I have lube.

You can clean the freewheel with a toothbrush and degreaser. To get deep between the cogs, use a strip of cloth as "floss". You can buy mineral spirits in jugs from your local hardware store. WD-40 will work as well.

From what I've been reading, WD-40 does not remove rust only prevents it so to say. So I put in the lubricant and the chain and the cassette, which is probably the better term than cog I suppose, and the color looks a lot better. The cassette still looks like it has black-rust on it though. Will a degreaser help with that? I've tried scrubbing with a toothbrush, without any real formulas though. What do you suggest I could buy, specifically, to aid me in removing this rust? Here's the lubricant I have been using. Btw, does lime away work well to get rid of rust? (in other areas as well?)

http://eheli.com.au/store/images/T/Triflow11.JPG

Take the cassette off and soak it overnight in vinegar. You'll need a cassette lockring and probably a chain whip to get the cassette off. What the vinegar doesn't dissolve you can scrape away with a toothbrush. Wash with water, dry, lightly lube with your Tri-Flow and reinstall. "Black rust" may just be gunk and not rust.

This is a rather extreme solution. Just oiling the chain and riding a mile or so while shifting through all the back gears should be enough.

Black rust is most likely on the Zinc Aluminum coating rather than the underlying steel. You can't rub it off with a toothbrush because it's not an expanded molecule like conventional rust, and does not flake. For all intents and porpoises you can just leave it, your cassette will be black from grease soon enough anyway.

The discussion comes up frequently whether to oil a new chain or leave that waxy crap they put on them at the factory. This is why you should oil the chain, because if you don't your cassette and chain will turn brown with rust the first time you get it wet. I left my well oiled chain sitting in the rain every day for two years while I was at University and never got so much as a spot of rust on it.

Just oil the cogs and brush them with a wire brush. Then clean them off a bit with some mineral spirits or WD40 to get rid of the brown rust sludge and re-oil them along with the chain. You don't need a fancy bike oil for this either. Just some regular engine oil will work if you have some. But if you have to go and buy something anyway then get a quart of Mobil 1 synthetic engine oil and you'll have a lifetime supply of top quality oil for your bicycle chain and many other uses. Get the thicker 20-50 if they have it so it doesn't wash out as easily.

And obviously if you value the investment in your bike you won't leave it outside anymore. It's one thing to ride it in the rain or even leave it locked to a bike rack in the rain. But leaving it out for storage in the rain is unforgivable on a lot of levels.

Check out the links in this thread.