2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 142Get this manual
Cylinder block Piston diameter a: 62.95062.965 mm (2.47832.4789 in) Measuring point b: 3.5 mm (0.14 in) up from the bottom of the piston skirt Oversize piston diameter: Oversize 1st: 63.20063.215 mm (2.48822.4888 in) Oversize 2nd: 63.45063.465 mm (2.49802.4986 in)
Checking the piston ring
1Measure the piston ring dimensions and TReplace the piston ring set if out of specification
Checking the cylinder bore
1Measure the cylinder bore (D1D6) at measuring points a, b, and c, and in direction (D1, D3, D5), which is parallel to the crankshaft, and in direction (D2, D4, D6), which is at right angle to the crankshaft
Piston ring dimensions: Top ring a: B: 1.171.19 mm (0.04610.0469 in) T: 2.302.50 mm (0.09060.0984 in) 2nd ring b: B: 1.171.19 mm (0.04610.0469 in) T: 2.42.6 mm (0.09450.1024 in) Oil ring c: B: 2.342.46 mm (0.09210.0969 in) T: 2.75 mm (0.1083 in)