7. CYLINDER HEAD/CYLINDER/PISTON ATV 50 The cylinder has an "A" mark or no A Mark mark on it. When replacing the cylinder with a new one, use a cylinder having the same mark as the old one. Measure the piston O.D. at a point 5 mm (0.2 in) from the bottom of the piston skirt. Service Limit: 38.9 mm (1.56 in) replace if below Measure the piston-to-cylinder clearance. Service Limit: 0.1 mm (0.004 in) replace if over Measure the piston pin hole I.D. Service Limit: 12.03 mm (0.481 in) replace if over Measure the piston pin O.D. Service Limit: 11.98 mm (0.479 in) replace if below Measure the piston-to-piston pin clearance. Service Limit: 0.03 mm (0.0012 in) replace if over 7-8