807166A2 Exhaust Water Shutter / Flapper Stops Water From Backing Up Into the Motor for MerCruiser 4.3L V6 GEN

Exhaust water shutter (rubber flapper) for MerCruiser
4.3L V6 GEN+ packages with a one-piece (batwing) exhaust manifold Y-pipe —
OEM 807166A2, cross pin about 2.98 inches. Helps stop seawater from washing back into
the riser and manifold on reverse, steep launch, following seas, or hard throttle chop
(hydrolock risk).
This is NOT 807166A1 (two-piece Y), NOT 807166A3 (old-pipe retrofit),
NOT early 3" 99370A2, and NOT tip-family 60930.

Which shutter is this?

OEM 807166A2 for the V6 one-piece manifold Y-pipe era (roughly 1996–1999;
confirm SN). Same numbers as 32-08307. Package: 1 × shutter (single piece) —
often sold with 2 grommets in retail kits. Not a pair of 17ST006.

Signs yours needs replacement

·       Cracked, missing, or stiff rubber flapper — water can wash back on reverse or steep launch

·       Idle clatter that fades with throttle — often blamed on lifters or the drive first

·       Fragments in the Y-pipe bottom or drive exhaust passage (found when changing the water pump)

·       Hydrolock or “gulped water” scare after reverse, ramp launch, or hard throttle chop

·       Power feels choked — debris from a broken flapper can restrict exhaust

·       Converted from one-piece to two-piece manifolds but the old Y-pipe stayed — still this family

·       Old part stamped 807166A2 or cross-ref 32-08307 · measured pin ≈2.98"

Transom bellows leaking at the drive? Different family (e.g. 17B1003) — not this shutter.

Will it fit my engine?

“4.3” alone does not prove fit. Confirm one-piece manifold Y, old number
807166A2, or pin ≈2.98". HP/year are coarse screens only — verify serial.
*Catalog years — confirm SN. Some retail ads say through 2001; we follow serial / part evidence.

OEM & swap numbers

Replaces ref 807166A2 · cross-ref 32-08307 · catalog 710-807166A 2w
(space spelling 807166A 2 in some PDFs).

Wrong shutter? Read before you order

·       NOT 807166A1 — two-piece / 4" Y shutter (GH 17ST002 / pair 17ST003) · pin ≈2.48"

·       NOT 807166A3 — old-pipe retrofit / offset (GH 17ST004 / 17ST005) · pin ≈2.50"

·       NOT 99370A2 / early 3" Y (GH 17ST006) — not a pair of this SKU

·       NOT 60930 tip / 4-cyl family (GH 17ST001)

·       NOT center-riser Y-pipe applications — measure pin / confirm casting

·       NOT a transom bellow — no bellows adhesive / expander job

What's in the box

·       1 × Exhaust water shutter (807166A2 equivalent) — single piece

·       Retail kits often include 2 grommets with the shutter — confirm photos / pack contents

·       NOT a “pair of 17ST006” — different OEM family entirely

Related GHMarine SKUs

·       Need two-piece / 4" Y shutter 807166A1? → GH SKU 17ST002 (single) / 17ST003 (pair)

·       Need offset retrofit 807166A3? → GH SKU 17ST004 / 17ST005

·       Need early 3" Y shutter 99370A2? → GH SKU 17ST006

·       Need tip / 4-cyl shutter 60930? → GH SKU 17ST001

Install tips

Work in a ventilated area. If unsure, use a marine shop.
Y-pipe flapper job — not a drive-off bellows adhesive job.

1. Confirm 807166A2 / 32-08307 / pin ≈2.98" on a one-piece manifold Y-pipe — not 2.48" A1, not 2.50" A3.

2. If manifolds were converted to two-piece but the original Y stayed, forum sticky still points to A2 — verify casting before ordering A1.

3. Shutter is cheap; stuck hoses and finding old debris are usually the hard parts.

4. If pieces are missing, dig the Y-pipe bottom and the drive exhaust passage before installing the new flapper.

5. Do NOT use bellows adhesive or an expander — flapper job, not transom bellow.

6. Wrong old number (A1 / A3 / 99370A2 / 60930)? Stop and order the matching GH SKU.

FAQs — the bros want to know

Is this the same as 807166A1?

No. 807166A2 fits the V6 one-piece (“batwing”) manifold Y-pipe (cross pin ≈2.98"). 807166A1 fits the two-piece exhaust Y-pipe (pin ≈2.48") — GH SKU 17ST002.

I converted to two-piece manifolds — do I still need A2?

Often yes. Forum sticky advice: if the original one-piece Y-pipe was not swapped when manifolds were converted, you still need 807166A2. Confirm Y casting / old shutter / pin size.

Is this a pair for 17ST006 / 99370A2?

No. 17ST006 is the early 3" Y-pipe shutter (99370A2). This SKU is a different part for GEN+ one-piece 4.3 packages. Company pair SKUs are 17ST003 / 17ST005, not 007.

Can I run without the shutter?

Some owners run calm water for a while. Reverse, steep launches, following seas, and hard throttle chop raise backflow / hydrolock risk. Replace a cracked or missing flapper.

Does “4.3” alone prove fit?

No. Same 4.3 can need A1, A2, A3, or even early 3" shutters. Match OEM number, Y-pipe, and ≈2.98" pin — serial ranges beat horsepower claims.

Do I need bellows adhesive?

No. That is for transom rubber bellows. This is a Y-pipe water shutter / flapper.

Please note

Aftermarket replacement part. Not OEM. Not affiliated with engine manufacturers referenced above. "Compatible with", "Replaces ref", and cross-ref numbers identify fitment — always confirm with your serial number, one-piece vs two-piece exhaust path, cross-pin size (≈2.98"), and old part number before ordering.