I bought a new bike second-hand recently and it's in good shape, but I wanted to get the rear cogs back to their true, shiny selves. I tried scrubbing them with Goo Gone and a tooth brush, but only the teeth broke free of the many layers of blackened, dried grease. A lot of people on here seem to recommend kerosene - will that do the trick? Or should I give up on this admittedly obsessive enterprise?

Kerosene or mineral spirits.
A tooth brush is fine. You can also "floss" between the cogs with a rag. The rag should be thick enough or doubled over so that you can work on two adjacent cogs simultaneously.

Al

the dried up grease can be scraped off with a plastic knife or butter knife.

you can use mineral spirits to clean off the wet grease or use a degreaser.

I keep a large box of qtips just for this purpose

Wrap a stiff piece of cloth around a thin metal ruler and sping the wheel backwards while holding the cloth between the cogs. You can use mineral spirits if the crud is too thick.

I think I'm going to go with mineral spirits as I've already got them on hand. Thanks a lot for the ruler idea, davidad! I've been using an old shirt to floss between cogs like Al said but it requires a small piece of cloth and a weird posture to get around the chainstay, so that will help.

You realize you can just remove the rear wheel from the bike to clean the rear cogs right.

foaming simple green works miracles, take the rear wheel off, coat it, let it sit. wipe and enjoy the shine.

Yeah, but mounting the bicycle on the stand puts the wheel at a convenient height and gives it an axle to spin around. I think taking it off would be more of a pain. How do you do it?

Thanks for the suggestion, too, zoodude.

By the time the cogs are caked in crud, the chain, chainrings, and derailleurs are in need of some serious cleaning, too. I generally remove the chain to put it in a plastic bottle with some kerosene and shake it up. This does a pretty good job of cleaning, but I end up wiping it down and putting it back in the bottle with fresh kerosene to get it down to truly clean. While all that is happening, I attack the dried gunk with anything that will scrape it off- usually a plastic scraper followed by cog flossing.

I've found Biodiesel to be an amazingly good solvent and it is non-flammable, non-toxic (but I wouldn't drink it) and doesn't really have any fumes. It is pretty cheap too - about the same as other diesel fuel and a lot less if you make it yourself.

Take the wheel off and place it on a table cog up. Flossing them becomes easy. As you pull in one direction, the og spins to a new location then pulling in the other direction the cogs lock and you get a good floss in that area. I usually take the cog off and soak it, but not necessary. You can soak it good with several methods noted. Scrapping through the thick stuff first saved a lot of time. You can also try flossing with some scotch brite pads and that will give it a little more abrasion and polish. I usually use a terry cloth towel doubled over. Enjoy