Different motorcycle engine repair projects vary in difficulty. If your engine locks up then you may need to install new pistons. This is a repair most owners can do themselves.
Step 1 – Remove the Pistons
Take the cover off of the engine. Remove the pistons by pulling up and sideways. Look for damage or wear of the pistons and cylinders. If you decide they need to be re-bored, you can get that done at a local machine shop. Take the parts that have been fixed and clean and dry them. Add some oil and clean the pistons as well.
Step 2 - Install the Rings
Clean the piston rings. Make sure the gap is set to the manufacturers specifications. You can measure this gap by inserting the ring in the cylinder and sliding it up until you have it about a half inch from the top. In this position you can determine the end gap. A gap that is too small can be remedied by using a file to take a small amount off of the ring ends. Take a very small amount at a time because if you get the gap too big you will need to use a new ring. Piston rings are easy to crack. If you need to make the gap wider try it with your hands. If you need to use the ring expander, do so carefully. Slip the rings over the piston until they are in the groove, being sure that you put the markings on the top side, if there are markings on the rings. You can get various types of rings. But when you are replacing the existing rings you need to get the same rings in the same size. You can lose compression if you get the wrong size. For a 3 piece ring, put all the rings in place then stagger the placement of the gaps so that they do not line up.
Step 3 - Install the Pistons
Oil the pistons, piston rings and cylinders well. Twist the pistons around in the groove to see if they have enough oil to move easily. Look at the markings on the piston. If there is a marking on the piston, that is the front side (exhaust side). Use a ring compressor. Push the piston and rings into the cylinder by putting it in from the top and pushing down past the wrist pin hole. Now put in the compression ring and push it down all the way. You may have to tap it with a mallet. Be sure to put on the gasket and the o-ring, if there is one your engine.
Step 4 – Put It Back Together
Now reinstall the engine cover and test the engine to see if it is running correctly.
Now that you have replaced the pistons you are ready to take it out for a spin. Enjoy the ride.