7. CYLINDER HEAD (2-STROKE)/ CYLINDER/PISTON VITALITY 50 Remove the piston rings and insert each piston ring into the cylinder bottom. Use the piston head to push each piston ring into the cylinder. 20mm Measure the piston ring end gap. Service Limit: Top: 0.5mm replace if over 2nd: 0.65mm replace if over Oil ring: 0.9mm replace if over Measure the piston pin hole I.D. Service Limit: 13.04mm replace if over Measure the piston pin O.D. Service Limit: 12.96mm replace if below 7-15