Skip to product information
Usually ships in 2–4 business days.
12644A1 18-4457 Exhaust 4in Protector Flapper for MerCruiser Mercury Sterndrive
$39.59
Sale price
$39.59
Regular price
Available to Order
This Exhaust 4��� Protector Flapper is a replacement exhaust shutter for MerCruiser and Mercury sterndrive systems and matches OEM Part# 12644A1, 18-4457.
Need help finding the right part? Talk with a parts expert today.
Parts Support Hours: Monday–Friday, 8:00 AM–5:00 PM CT
Live Chat: Available 24/7
I needed a forklift part and wasn’t sure which one fit. They asked for the model and serial number, got back to me quickly, and made sure I ordered the right one. Really helpful.
Randy W. — Verified customer
Product Overview
This exhaust protector flapper is a 4-inch diameter shutter that prevents water from entering the engine through the exhaust outlet when the boat is not running. It fits MerCruiser and Mercury sterndrive exhaust systems, providing essential protection against engine damage from backflow. The flapper assembly is a direct replacement for worn or missing exhaust shutters.
Key Features & Performance
- Direct replacement for OEM part numbers 12644A1 and 18-4457
- 4-inch diameter flapper fits standard MerCruiser and Mercury exhaust outlets
- Stainless steel hinge pin for corrosion resistance
- Rubber flapper closes automatically when engine is off to block water entry
- Durable construction withstands exhaust heat and marine environment
- Easy bolt-on installation without special tools
Fitment & Compatibility
- MerCruiser sterndrive models with 4-inch exhaust outlets
- Mercury Marine sterndrive models with 4-inch exhaust outlets
- Compatible with many Alpha One, Bravo One, Bravo Two, and Bravo Three drives
- Fits most MerCruiser V6 and V8 gasoline engines with transom exhaust systems
Common Uses
- Replacing broken, missing, or stuck exhaust flappers on sterndrive boats
- Preventing water from siphoning back into the engine via the exhaust system
- Restoring proper exhaust system function after flapper wear or failure
Technical Specifications
- Part Number(s): 12644A1, 18-4457
- Flapper Diameter: 4 inches
- Material: Rubber flapper with stainless steel hinge
- Mounting: Bolt-on
- Application: MerCruiser and Mercury sterndrive exhaust outlets
Frequently Asked Questions
Q: Will this flapper fit a MerCruiser 5.0L Alpha One? A: Yes, this 4-inch protector flapper is compatible with most MerCruiser Alpha One sterndrive models equipped with a 4-inch exhaust outlet, including 5.0L engines.
Q: How do I know if my old flapper needs replacing? A: If the flapper is cracked, missing, or does not close fully when the engine is off, it should be replaced to prevent water ingress into the exhaust system.
Product appearance and specifications may vary slightly by batch. Compatibility may vary by serial number. Verify fitment before purchase.