Bicycle chains are the most integral part of machine because they allow the mechanical force of the pedals to be transferred to the wheels creating motion. When a chain becomes rusted, its pliability is removed from the oxidizing and the correct motion cannot be achieved. In many cases, minimal chain damage can be fixed with very little effort. Fixing the chain is helpful if the bike receives minimal use, or will quickly be outgrown by a child. In these instances it is often more economical and time effective to merely fix the chain rather than replace it.
Step 1 - Assessing Damage
Some of the most common damage is minor pitting, surface rust to the outside of the links or stiffness. These issues can be resolved. However, if you see compromised structural integrity to the chain, you should replace the chain because of safety and struggles with riding. Fortunately, a replacement chain is often under $15.00.
Step 2 - Remove the Chain
For single speed, or three speed bikes, as well as children's bicycles, there is a master link. When the links are pried apart, the chain will come off. The master link is usually a different color and distinctly different. Use a flat head screw driver to pry the side plate open. For geared bikes a chain tool is necessary. If using a chain tool, be sure the center pin does not completely come out.
Step 3 - Soak the Chain
Place the chain in a mason jar and fill with either kerosene or gasoline. This will break up any debris, sediment, gunk and begin to break down any accumulated rust. Let the chain soak for 24 hours in a well ventilated area with the lid removed.
Step 4 - Scrub With a Towel
Use rubber gloves when handling the chain and be careful to avoid any chemical splatter. Make sure that all of your clothes and towels can be permanently stained, since this is a very messy process. Scrub the chain down with a towel while working each link back and forth to remove any internal buildup. The chain should be pliable when finished. If it is not, re-soak it for another 24 hours.
Step 5 - Reattach the Chain and Apply Degreaser
Place the chain back onto the bike by either reattaching the master link, or resetting the center pin. Use bicycle degreaser at half strength, one part degrease and one part water, to clean the chain of any remaining debris. Spray down the chain liberally. Work the pedals to run the chain through the rear cassette and front cog. Next, halfway between the front cog and rear derailer, hold a towel snugly to the chain and rotate it through to pull gunk away. Run the chain through 4 to 6 revolutions. Wipe down cogs to remove any splattered debris.
Step 6 - Lubricate
Using bicycle chain lubricant liberally, apply several drops of lubricant on each chain link and rotate the chain. If you are using a geared bike, be sure to switch through all gears fluidly to distribute the lubricant. After 3 complete rotations, wipe off excess lubricant.