2003 ST 4 Stroke 9.9/15HP Johnson outboards Service Manual, Page 136Get this manual
POWER UNIT CYLINDERCRANKCASEPISTON ASSEMBLY Piston ring thickness Standard: 1st and 2nd 1.17 -1.19 mm (0.04610.0469 in) Piston ring to groove clearance Standard: 1st and 2nd 0.020.06 mm (0.00080.0024 in) 1st and 2nd 0.10 mm Service limit: (0.0022 in)
If exceed service limitReplace: Piston andor Piston ring NOTE: Using soft-metal scraper, decarbon the crown of the pistonClean the ring groove similarly
Piston Ring End Gap
Measure: End gap
Thickness gauge
Piston ring end gap Standard: 1st2nd 0.100.25 mm(0.0040.010 in) Service limit: 1st and 2nd 0.5 mm (0.02 in)