1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 203Get this manual
CYLINDER BLOCKCRANKCASE
PISTON RING END GAP CLEARANCE 1Measure piston ring end gap clearanceReplace piston ring if out of specification
NOTE: Ring should be level for measurement, push ring into bore with crown of piston
a-0.8 mm (20 mm) Depth Piston Ring End Gap Top 2nd Oil 0.0060.012 in(0.150.30 mm) 0.0120.020 in(0.300.50 mm) 0.0080.028 in(0.200.70 mm)