To refit the original
Pistons, carefully remove the piston rings and clean the grooves and rings to eliminate carbon, ensuring not to scratch the aluminium surfaces. If new rings are being installed, order the top compression ring to be stepped to avoid contact with the wear ring likely formed at the top of the cylinder bore. Before fitting the rings, push each ring down into its respective cylinder bore using an inverted piston to maintain squareness and measure the ring end gap. Test the side clearance of the compression rings, and if a ring is slightly tight in its groove, it can be rubbed down while keeping it square on an oil stone or fine emery cloth on plate glass; excessive tightness requires machining of the grooves. The gudgeon pin should fit snugly into the piston at room temperature; if it is loose, both the piston and gudgeon pin need replacement.