39-21665A12 – Piston Ring Set – Mercury

39-21665A12 piston ring set is an OEM-spec ring kit for small-cylinder Mercury outboards (3.5–9.8 HP). It delivers the correct piston-to-cylinder wall seal, restoring compression and reducing blow-by and oil consumption.

This set covers standard-bore pistons commonly found in early Mercury outboard motors. Replacement rings like these are essential after cylinder wear or any re-bore work to maintain optimal engine efficiency.

Install the 39-21665A12 piston ring set when you notice rough idle, decreased power, smoky exhaust, or increased oil usage. The correct ring fit ensures smooth combustion, reliable performance, and extended engine life.

Shop at Arizona Outboard Dismantlers to keep your outboard running strong and ready for the water.