89260 Exhaust Flapper & Clamp for 5" & 6" Outlets | JLM Marine

Exhaust Flapper & Clamp for 5" & 6" Outlets – Universal Marine Backflow Preventer

This exhaust flapper and clamp assembly is designed to fit marine engines with 5" or 6" exhaust outlets. It functions as a backflow preventer, stopping water from entering your engine through the exhaust system when the boat is at rest or during wave action. The adjustable stainless steel clamp allows for installation on both outlet sizes—simply trim the band to fit 5" applications.

This aftermarket replacement directly crosses to Sierra 18-4458, OEM 89260, and multiple other part numbers listed below. It provides reliable protection against exhaust backflow at a competitive price point.

• Fits 6" outlets without modification; trim clamp band for 5" outlets
• Includes flapper valve and stainless steel adjustable clamp
• Prevents water intrusion through exhaust during idle or reverse flow conditions

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

This exhaust flapper is a universal fit for marine engines equipped with 5" or 6" exhaust outlets. Verify your outlet diameter before ordering.

Technical Specifications

Package Contents

• 1 × Exhaust flapper valve
• 1 × Stainless steel adjustable clamp

Installation Guide

1. Measure your exhaust outlet diameter to confirm it is 5" or 6". For 5" outlets, you will need to trim the clamp band.
2. If installing on a 5" outlet, use tin snips or metal shears to carefully cut the stainless steel band to the proper length for a 5" diameter circle.
3. Slide the clamp over the exhaust outlet with the flapper valve positioned to open outward (away from the engine).
4. Position the flapper so it hangs vertically when the boat is level. Ensure the hinge is at the top.
5. Tighten the clamp securely using a screwdriver or nut driver, ensuring even pressure around the circumference.
6. Check that the flapper moves freely and is not binding on the outlet or clamp hardware.
7. Start the engine and verify exhaust gases push the flapper open during operation.
8. Shut down the engine and confirm the flapper closes fully to prevent backflow.
9. Inspect the clamp periodically for corrosion or loosening, and replace the flapper if cracking or stiffness develops.

Troubleshooting & FAQ

Q: How do I know if I need a 5" or 6" flapper?
A: Measure the outer diameter of your exhaust outlet pipe. This flapper fits both sizes—use it as-is for 6" or trim the clamp band for 5".

Q: How do I trim the clamp for a 5" outlet?
A: Use tin snips or aviation shears to cut the stainless steel band to match a 5" diameter. Test-fit before final tightening to ensure proper overlap and tension.

Q: How often should I replace the exhaust flapper?
A: Inspect annually or whenever you notice reduced engine performance, water intrusion, or visible cracking in the rubber. Replace every 2–3 years in harsh saltwater environments.

Q: The flapper won't close fully—what's wrong?
A: Check for debris or salt buildup on the hinge and flapper surface. Ensure the clamp is not over-tightened, which can distort the outlet and prevent proper sealing.

Q: Will this fit my sterndrive or inboard engine?
A: Yes, as long as your exhaust outlet is 5" or 6" in diameter. Measure carefully to confirm fitment.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.