Mercury Force 9.9, 15HP Outboards Service Manual, Page 135Get this manual

13Measure piston pi bore with micrometer inside

NOTE: Piston pin must fit snugly in pin bore
14Measure piston ring end gap Insert new piston ring into cylinder just above exhaust port

NOTE: Use one of the pistons to slide ring in

• ATV
• Jet Ski
• Outboard Motors
• Personal Watercraft
• Snowmobiles
• Stern Drives