One of the easier fixes for the motorcycle rider is installing new motorcycle piston rings. If you've removed the pistons and the damage is more severe, you might need to have the motorcycle engine re-bored. You'll need new pistons and rings then, too. The procedure is the same in both cases.
Step 1 - Prepare the Pistons and Cylinders
Remove the engine cover and pistons. Pull the pistons up and to the side. Check the pistons and cylinders for sign of wear or damage. If you find they need re-boring, send them out to a machine shop for the work. When you receive the rebored cylinders back, wash them well with soap and water. Dry them, then clean and oil the cylinders. Clean the new larger pistons by wiping them down.
Step 2 - Prepare the Rings
Wipe down the rings, making sure they are clean and smooth. You'll see that each ring has a very small gap that is set to the engine manufacturer's recommendations and based on the size of the bore. This can vary between .08 and .25 millimeters. You measure it by placing the ring in the cylinder and pushing it to within one half inch of the top of the cylinder. Using the piston to do this squares the ring and guarantees an accurate measurement. If the rings don't meet specifications, adjust them by very carefully filing the ends of the ring.
Step 3 - Install the Piston Rings
Piston rings are hard and brittle and break easily. You can use a ring expander to stretch the rings for the piston, or you can use your fingers. The danger of using the ring expander is over spreading the ring and snapping it. Different types of engines use a different number of rings, too. On a four stroke engine, you can have a one-piece ring or a three-piece ring. One at a time, slide the rings down the piston and into the grove near the top. Be careful not to twist or overlap them. If using the three-piece ring, stagger the gaps around the piston one-half to one-third rotation to help maintain compression.
Step 4 - Replace the Pistons and Engine Top
Make sure entire surface of the rings, piston, and cylinders is oiled well. Replace the pistons and engine cover by reversing the pattern you used when you removed them.
Remember: Piston rings are made different sizes to fit different engines. Always use the recommended size piston ring. Trying to improve the engine compression by using a large size ring only results in an incomplete seal between the piston and the cylinder.