2003 ST 4 Stroke 9.9/15HP Johnson outboards Service Manual, Page 134Get this manual
POWER UNIT CYLINDERCRANKCASEPISTON ASSEMBLY Inspect: Water jacket Clog, obstructionClean
Cylinder Bore Wear
Measure: Cylinder bore (in thrust and axil directions at three elevations )
Cylinder gauge set
Cylinder bore wear (Distance between thrust and axil measurement) Service limit: 0.055 mm (0.0022 in) If exceeds service limitReplace or Rebore
Piston to Cylinder Clearance
Measure: Cylinder bore Piston diameter Cylinder measuring position: 50 mm (2.0 in) from cylinder top surface Piston measuring position: 15 mm (0.6 in) from piston skirt end Micrometer