In most cases, a rusty motorcycle chain is not a safety issue. Unless the chain is rusted all the way through, your bike is not going to stop running or fall apart. However, rust detracts from the overall beauty and elegance of your bike. While you can remove the chain from your bike in order to clean it, it is not necessary to remove rust.
Put blocks under your bike so the rear tire is elevated off the ground. This allows you to spin the rear tire and easily move the chain into position for cleaning.
Cover as many exposed parts of your bike as possible with large cloths or shop rags. As you scrub the chain, cleaner and debris will splatter.
Spray both sides of the chain with WD-40. Allow it to soak into the chain for five minutes.
Put on protective goggles. Spray WD-40 onto a fingernail cleaning brush and vigorously brush both sides of the chain. Work in small sections, getting the chain as clean as possible. Spin the rear tire of the bike to move the chain as you clean.
Wipe the chain off and inspect for any remaining rust. Respray any rusty spots with WD-40 and allow it to soak in for 5 minutes. Spray your fingernail cleaning brush with WD-40 and scrub any difficult spots until they are clean. Wipe as much WD-40 off the chain as possible with a clean cloth.
Spray your chain with motorcycle chain lubricant. Pay special attention to the O-ring at each link connection.
You can substitute kerosene for WD-40.
Use WD-40 in a well-ventilated area.