2009 Yamaha F40 Outboard Service Manual, Page 234Get this manual
Cylinder block
Checking the piston ring end gap
1Level the piston ring in the cylinder with piston crown2Check the piston ring end gap at the specified measuring point b
Checking the piston ring side clearance
1Measure the piston ring side clearanceReplace the piston and piston ring set if out of specification
Piston ring side clearance: Top ring a: 0.020.06 mm (0.00080.0024 in) Second ring b: 0.020.06 mm (0.00080.0024 in) Oil ring c: 0.040.18 mm (0.00160.0071 in)
Piston ring end gap (reference data): Top ring: 0.150.30 mm (0.00590.0118 in) Second ring: 0.300.50 mm (0.01180.0197 in) Oil ring: 0.200.70 mm (0.00790.0276 in) Measuring point b: 10.0 mm (0.39 in)