89260 5/6-Inch External Exhaust Flapper · Fits MerCruiser 5-inch and 6-inch OD through-transom exhaust outlets, Replaces 18-4458, 9-44002

89260 5/6-Inch External Exhaust Flapper · Fits MerCruiser 5-inch and 6-inch OD through-transom exhaust outlets, Replaces 18-4458, 9-44002

GHMarine 5/6-inch external exhaust flapper for through-transom exhaust outlets with 5-inch or 6-inch OD. Primary catalog number 89260; cross-refs 18-4458 and 9-44002. There is no verified Mercury OEM parent number for this family. This is an external flapper on the hull outlet — not a rubber bellow and not a Y-pipe internal water shutter (807166A1 / A2 / A3).

Catalog packaging for this family is typically 1 flapper with clamp. Confirm the exact contents against your package photo / packing slip before install.

Which flapper is this?

This is the larger external rubber flapper for through-transom outlets measuring 5 inch or 6 inch OD. Same job as the 4-inch external flapper family, but a different outlet size — they are not interchangeable.

It is not the 4-inch external flapper (12644A1 / 89250 — GH 19B1002), not the 3-inch external flapper (89240 family), and not a Y-pipe internal shutter (807166A* — GH 17ST00x).

Signs yours is due

• Measure the through-transom exhaust outlet OD at about 5 or 6 inches — the larger external flapper (89260 family) is cracked, cupped, or missing.
• Following-sea water slap at the big tip outlet; the 4-inch flapper kit will not cover this OD — confirm 5/6-inch before you order.
• External clamp on the 5/6-inch tip is gone or cut into the rubber; the flapper no longer seats on the outlet lip.
• Divert: outlet is clearly 4-inch / 12644A1 → GH 19B1002. Internal Y-pipe shutters 807166A1/A2/A3 → shutter SKUs, not 23EF445.

Will it fit my drive?

This flapper is Compatible with marine through-transom external exhaust outlets where the outlet OD is 5 inch or 6 inch and the old part / catalog number falls in the 89260 family. Engine horsepower alone does not prove fit — measure the outlet OD and match the old number.

If your outlet is 4 inch (GH 19B1002) or 3 inch, or your old shutter is an 807166A* Y-pipe piece, stop — this listing is the wrong family.

OEM & swap numbers

Primary catalog number is 89260. No verified Mercury OEM parent number for this SKU. Cross-ref numbers below identify the same 5/6-inch external flapper family.

Wrong part? Read before you order

• NOT a 4-inch external flapper (12644A1 / 89250 — GH 19B1002)
• NOT a 3-inch external flapper (89240 family)
• NOT a Y-pipe internal water shutter (807166A1 / 807166A2 / 807166A3 — GH 17ST00x)
• NOT a rubber exhaust bellow / transom boot (8M0124227 — GH 17B1003)
• NOT selected by engine HP or displacement alone — measure outlet OD

What ships in the box

• 1 × 5/6-inch external exhaust flapper (89260 family)
• Clamp: catalog packaging typically includes 1 clamp — confirm against your package before install

Often ordered with related SKUs

• Need 4-inch external flapper → GH 19B1002 (12644A1 family)
• Need Y-pipe internal shutters 807166A3 → GH 17ST004 / 17ST005
• Need twin-engine 4-inch bellows + A3 shutters → GH 18BS002
• Need transom exhaust bellow → GH 17B1003

Install tips on the through-transom outlet

External hull outlet work. If you are not comfortable working at the transom exhaust outlet, use a marine shop. Do NOT use bellows adhesive or a bellows expander — those are for rubber bellow boots, not this flapper. Do NOT pull the sterndrive to install this part.

1. Confirm outlet OD is 5 inch or 6 inch and the old number is in the 89260 / 18-4458 / 9-44002 family (not 4 inch / 3 inch / 807166A*).
2. Remove the old flapper and clamp; clean the outlet lip.
3. Seat the new flapper fully on the outlet; install the clamp if supplied in your package; tighten securely.
4. Check free movement of the flapper — it must open with exhaust flow and close when reverse water pressure hits the outlet.
5. Run and inspect for spray / leaks at the outlet before returning the boat to service.

FAQ

Is this a bellow or a flapper?

Flapper only. It mounts on a through-transom external exhaust outlet. It is not a sterndrive exhaust bellow and does not use bellows adhesive or an expander tool.

Will it fit my MerCruiser by horsepower?

No. Fit is by outlet OD (5 inch or 6 inch) and the 89260 part family. Horsepower and displacement alone do not prove fit.

Is this the same as 19B1002 / 12644A1?

No. 19B1002 is the 4-inch external flapper family. This listing is 5/6-inch only.

Is this the same as 807166A1 / A2 / A3?

No. Those are Y-pipe internal water shutters. This SKU is an external through-transom flapper on the hull outlet.

What comes in the box?

One 5/6-inch external flapper. Catalog packaging typically also includes one clamp — confirm against your package photo / packing slip.

Do I need bellows adhesive or an expander?

No. That is for rubber bellow boots such as GH 17B1003. This flapper seats on the outlet and is retained with a clamp when supplied.

Please note

Aftermarket replacement part. Not affiliated with engine manufacturers named above. "Compatible with", "Replaces", and cross-ref numbers identify the 5/6-inch external flapper family — always confirm outlet OD, old part number, and package contents before ordering.