Mercruiser V6/V8 I/O exhaust shutters explained. (only applies to 4" systems)

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
(EDIT: There is a parts list in last post of this thread)

There seems to be a lot of confusion around exhaust shutters for SBC and V6s I/Os.. (this also applies to most BBC as well).

From the start of the 'R' series and the new inner transom plate (1982), up to about 1995 the shutters used were the single plate on a shaft type. These worked well, until they didn't. Given enough time the tabs on the shutter that sit on the shaft would eventually wear though the shaft. If you're mildly unlucky the shutter will lodge in the bottom of the Y-pipe and eventually wear a hole through it. That will let water into the boat... Not good!. I know this from first-hand experience :eek:

Once Merc realised the problem with the old style shutter they redesigned them and the Y-pipe. The new Y-pipe is used from about 1996 (corresponds roughly with the advent of the Vortec heads). The new style shutters are a 2 piece 'clapper' design and the part number is -807166A1, with one notable exception, the 'batwing' (single piece) manifolds of the V6. It has a different Y-pipe and so a different shutter. The number for those shutters is -807166A2. By now we hope all batwings have been replaced with the more conventional 2 piece system. But the shutters remain the same, the A2 number. (unless the Y-pipe has also been changed in the conversion).

If you have a pre-96 engine and need to replace the shutters, they supersede to the new design and the number is -807166A3. It comes assembled with a carrier to fit straight onto the top of the old Y-pipe. When this shutter needs replacing, you use the same number.

So, in brief.
-807166A1... for new style (1996 and on) Y-pipe (except batwing V6s).
1637188302791.png

-807166A2... for batwing V6 manifolded engines. Or ones that have been converted, but still have the original Y-pipe.
1637188476912.png

-807166A3... replacement for all old style (1982-1995) shutters. Use this number when replacing them too.
1637188391256.png


Chris...
(At the bottom of this thread is a new post with all the part numbers, and what you need if you plan on converting to dry-joint exhausts.)

The difference between 'wet joint' and 'dry joint' exhaust systems explained.

Line drawing of the old and new style shutters.

Shutters, old, new.jpg
 
Last edited:

Volphin

Lieutenant
Joined
Jun 5, 2011
Messages
1,405
I concur Moose. Chris, this would make a helpful sticky as does come up so often.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Ayuh,.... I ain't opposed to that idea, at All,....
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,319
Nice write up Chris. Good job! And I agree, throw it in the adults only section.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Thanks for the support guys... It's now linked in the sticky section. I did this because, as Volphin pointed out, it does come up a few times, and there's always confusion... Hopefully, a lot less now.. :)

Chris.........
I'll see what I can do about photos and I'll add as I can.
 
Last edited:

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
After a few false starts I have eventually made a fairly full list of the parts Merc have used over the years with the different exhausts. This just applies to stern drive engines, not inboards. If people think I should add inboard part numbers, let me know.

Wet joint
Manifolds
V6 – 99746A17
V8 – 860246A15

7° (4”) parts

Exhaust elbow – 807988A03
Inter elbows (with NO riser)
V6 - 14478T01
V8 - 11086T (port)
V8 - 14343T (stbd)
Y-pipe - 807130A4 (Originally -44266T)

14° (3”) parts

Exhaust elbow – 98504A3
Inter elbows (with NO riser)
V6 – 99758A1
V8 – 94444A1 (port)
V8 – 94443A1 (stbd)
Y-pipe - 99877A10

Dry Joint
Manifolds
V6 – 864612T01
V8 – 865735A02

7° parts

Exhaust elbow – 864309T02
Inter elbow (with NO riser)
V6 - 14478T01
V8 - 11086T (port)
V8 - 14343T (stbd)
Y-pipe - 807130A4

14° parts

Exhaust elbow – 864591T02
Inter elbow (with NO riser)
V6 - 865947A01
V8 - 865951A01
Y-pipe - 807130A4

Chris.......
 
Last edited:

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,759
(EDIT: There is a parts list in last post of this thread)

There seems to be a lot of confusion around exhaust shutters for SBC and V6s I/Os.. (this also applies to most BBC as well).

From the start of the 'R' series and the new inner transom plate (1982), up to about 1995 the shutters used were the single plate on a shaft type. These worked well, until they didn't. Given enough time the tabs on the shutter that sit on the shaft would eventually wear though the shaft. If you're mildly unlucky the shutter will lodge in the bottom of the Y-pipe and eventually wear a hole through it. That will let water into the boat... Not good!. I know this from first-hand experience :eek:

Once Merc realised the problem with the old style shutter they redesigned them and the Y-pipe. The new Y-pipe is used from about 1996 (corresponds roughly with the advent of the Vortec heads). The new style shutters are a 2 piece 'clapper' design and the part number is -807166A1, with one notable exception, the 'batwing' (single piece) manifolds of the V6. It has a different Y-pipe and so a different shutter. The number for those shutters is -807166A2. By now we hope all batwings have been replaced with the more conventional 2 piece system. But the shutters remain the same, the A2 number. (unless the Y-pipe has also been changed in the conversion).

If you have a pre-96 engine and need to replace the shutters, they supersede to the new design and the number is -807166A3. It comes assembled with a carrier to fit straight onto the top of the old Y-pipe. When this shutter needs replacing, you use the same number.

So, in brief.
-807166A1... for new style (1996 and on) Y-pipe (except batwing V6s).
-807166A2... for batwing V6 manifolded engines. Or ones that have been converted, but still have the original Y-pipe.
-807166A3... replacement for all old style (1982-1995) shutters. Use this number when replacing them too.

Chris...
(At the bottom of this thread is a new post with all the part numbers, and what you need if you plan on converting to dry-joint exhausts.)

Line drawing of the old and new style shutters.

View attachment 189689
Excellent information but I can't enlarge diagram to fully view! I had an 86 SR Amberjack back in the 90s (v8S) that didn't have any shutters. My 1995 Proline (V8s) did. My recent 86 restoration did have them but one motor's was almost disintegrated. I also had to buy new Y pipes due to salt water corrosion. One new pipe had notches for the new style shutters (I assume) . The other one didn't. I had to notch the older pipe. I could not see or notice any major differences in the pipe other than notches. If there are, please let me know. THX
 
Top