Sierra 18-2732-9 MerCruiser Exhaust Water Shutter Flapper - Pack of 2

The Sierra 18-2732-9 is a pack of two exhaust water shutters (also known as exhaust flappers) engineered to OEM specifications for MerCruiser sterndrive and inboard applications. These 4-inch bell-type shutters are constructed from rubber and steel and are direct replacements for MerCruiser OEM part number 807166A3.

Water shutters serve as one-way valves installed at the top of the exhaust "Y" pipe where each leg meets the rubber exhaust elbow leading to the exhaust riser. When the engine is running, exhaust pressure pushes the shutters open. When the engine is off, the shutters spring closed to prevent water from traveling back into the exhaust risers, manifolds, or engine cylinders — protecting your engine from costly water ingestion damage.

These shutters feature a tabbed snap-in design — two tabs molded into the sides snap directly into the mounting holes, eliminating the need for pins or grommets.

Key Features:

• Bell-type exhaust water shutter (flapper) — sold as a pair
• 4-inch exhaust shutter size
• Rubber/steel construction for durability and heat resistance
• Tabbed snap-in mounting — no pins or grommets required
• Engineered to meet OEM specifications
• Replaces MerCruiser OEM part number 807166A3

OEM Cross-References:

• MerCruiser: 807166A3, 1438A1, 14348, 14348A2
• Mallory: 9-42802
• GLM / Redline: 89170
• Pro Marine: 65166

Water shutters are exposed to repeated heat cycling and saltwater environments that accelerate wear and corrosion. Routine inspection and replacement is strongly recommended to safeguard your engine investment.