You are doing lawn mower repair when you may need to remove the piston. You have to inspect the rings and ring grooves for any damage. Usually, you may not need to remove the rings from the piston. It should be avoided actually in order to minimize the chance of breakage. Is the other surface of the rings has pits, corrosion, or scratches? That should not be the case for the appearance of the rings should be free from chips or any other damage visible to the eye. Use a ring expander if ever you need to remove the rings. Note the orientation of the rod and pin when you need to remove the piston pin as they must be returned in their proper placement. You have to remember that pistons are not symmetric, so you have to know note the orientation so you know where to put them back.