When modifying your motorcycle you may choose to change the size of your sprockets to affect your gear ratio. In changing sprocket size, you will also need to adjust the length of your chain. The easiest way to do this is to purchase a stock length so you can cut the motorcycle chain to fit your new sprockets. While you can purchase official chain breaker tools, you can cut a motorcycle chain using just a few common tools you probably already have. The key is to remember that you really aren't cutting anything at all.
Identify the length of chain that must be removed to provide you with the right size drive chain for your motorcycle. Use a white paint pen to mark the link where you need to "cut" the motorcycle chain.
Grind the top and bottom heads off the rivets connecting your marked link to the rest of the chain.
Lay the chain on your work surface, near the edge, and attach two c-clamps on either side of the link that you ground the rivet heads off. You want the chain to be "standing up" just as it would be on your sprockets and not lying on the link faces.
Pry the face of the link off the ground rivets. Use a hammer to work your large flathead screwdriver like a chisel as the faces of the link will be tightly pressed onto the rivet body. When the face of the link comes off, dissemble the rest of that link (it will pull apart easily with the face off) and discard the chain you have now "cut" from the length you need.
Spray some WD-40 on the link before you attempt to pry the face off the rivet pins. This will help free the face.
Always wear gloves and safety glasses when attempting to cut a motorcycle chain. Grinding metal or even prying the face off can cause serious eye and hand injuries if the metal flies free and you are not adequately protected.