If your chain doesn’t respond to the wipe-down treatment, you must get serious. Dirty, oily chains need degreaser to clean them up. This is strong stuff, so take care not to let it seep into bearings, where it breaks down the grease that keeps things well lubricated and running smoothly.
A chain box helps keep you and your chain clean
I prefer liquid degreaser, which you can apply with a brush, to the spray cans. Spray is more wasteful and harder to direct accurately. But whether you use spray or liquid, you need a brush. Washing-up brushes work well; they’re cheap and you can buy them in regular shops. Bike shops sell special sets of brushes, but my favourites are paint brushes. You can cut off the bristles about halfway down, so what remains is firm but flexible. Keep the brushes you use for your drivetrain separate from those for frames, rims and disc rotors. Use rubber gloves to protect your hands from the degreaser.
Take your bike outside, as this business always gets messy. Keep the bike upright, with the chain in the largest chainring at the front. Dip the brush into the degreaser and work it into each link in the part of the chain that’s wrapped around the front chainring. Do both sides, then turn the pedals around and work on the next section of chain. It takes a few minutes for the degreaser to work, so let it soak in, working around until you are back where you started.
Clean the chainrings next, front and back, picking out anything that’s stuck between the chainrings or between the outer chainring and the crank arm. Clean up the derailleurs and the jockey wheels on the rear derailleur too, otherwise they dump dirt straight back onto the clean chain. Hold the back wheel upright and scrub the cassette clean. If there is compacted muck stuck between the sprockets, scrape it out with a stick or skewer. You can buy a special little brush if you want but remember: the world is full of sticks, which cost nothing. Be especially careful with the degreaser at this point: keep the wheel upright to prevent it from getting into the rear hub or into the freehub (the ratchet mechanism inside the cassette).
Using a clean brush, rinse off all the degreaser with warm water. Jetwashing may be tempting but don’t – ever! The protective bearing seals cannot withstand jet-wash pressure and the grease that makes bearings run smoothly is soon displaced by water. If your drivetrain is really dirty, you may now decide to repeat the job. Once everything is as clean as possible, dry the chain by running it through a clean rag and re-lubricate. Sprockets and chainrings don’t need lubrication. Pop a drop of oil on the derailleur pivots, front and back, and wipe off the excess, otherwise it just collects dirt.
A tidier option for regular cleaning is a chain-cleaning box. This is a case that fits over the chain, with little brushes inside that scrub the chain clean. Fill the reservoir with degreaser, then snap the box over the lower section of chain.
Pedal slowly backwards. Most boxes have a button that you press to release degreaser onto the chain. Don’t pedal too quickly or you’ll splash degreaser out of the back of the box. Keep going slowly until you’ve used up all the degreaser. Unclip the box and take a fiveminute break to give the degreaser time to break down the dirt.
Rinse off with clean, warm water. If your chain was extremely dirty, you might repeat the process. Dry your chain with a clean rag and re-lubricate. It’s worth cleaning the chain box with a little fresh degreaser straight away, so it is ready for next time.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Chain hygiene: regular chain wipe-down”