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Discussion Starter · #1 ·
Both of the exhaust flappers in my y-pipe are missing in action. I can not find the exhaust system parts on mercruiserparts or any other sites. This is a 91' setup with the one piece y-pipe. I found one of the flappers stuck in the lower part of the pipe and they look to be just a one piece flapper. Does anyone know the part number for these I will try to upload a picture later on if that will help. Also where I run with the Merc style silent choice through the transom 95% of the time do these y-pipe flappers serve their purpose?
 

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From what I know, there is two different kind, one for 3'' pipe and another one for 4'' pipe.


This is a Water Shutter used in the Y-Pipe on a Mercruiser Sterndrive. It will fit V-6 & V-8 Engines from 1982-87 with a 3 inch Exhaust Y-Pipe. This item replaces: Mercruiser # 99370A2




This is an Exhaust Water Shutter for a Mercruiser Sterndrive. It is used in the 4.0" Exhaust Y-Pipe 1987 & Up. These Water Shutters are sold as Each. This item replaces Mercruiser 807166A3 & 14348T.


As far as I'm concern, on my 88 7.4 with Bravo 1, I have the 3 inch model.
 

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the flappers probably dont matter too much with a single motor. they are designed to stop water from comming back up through the pipe and into the motor. this only will happed if the motor is shut off and water is forced up the pipe.

reason I say its not a big deal with a single is that you cant back up while the motor is off. now with twins you can have one motor shut off, and the other one in reverse. if your drive on the side that is not running is not all the way down water will get forced up the Y-pipe and fill your motor with water.

Been there, done that.....tore the motor apart thinking I had major issues because the motor was full of water. when we couldnt find anything wrong with the motor I started looking elsewhere......found the flappers missing on that side and I happened to move the boat with just the other motor right before it happened. it took me a while to put 2+2 together...but I finally figured it out. only cost me 3 days of my time and an unnesessary motor tear down :rolleyes:
 

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I just replaced mine with the 4in model. The 3in model is for older boats. Mine looked identical to the first pic. I got mine from ebasic from Mallory. About 30 bucks for the pair. As with even the merc brand ones they still need some trimming around the rubber to move freely.
 

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Discussion Starter · #8 ·
I have the offset one that has part number 14348 stamped on the stainless steel. I guess it is MERC part number 14348A2
 

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MarkyMark said:
the flappers probably dont matter too much with a single motor. they are designed to stop water from comming back up through the pipe and into the motor. this only will happed if the motor is shut off and water is forced up the pipe.

reason I say its not a big deal with a single is that you cant back up while the motor is off. now with twins you can have one motor shut off, and the other one in reverse. if your drive on the side that is not running is not all the way down water will get forced up the Y-pipe and fill your motor with water.

Been there, done that.....tore the motor apart thinking I had major issues because the motor was full of water. when we couldnt find anything wrong with the motor I started looking elsewhere......found the flappers missing on that side and I happened to move the boat with just the other motor right before it happened. it took me a while to put 2+2 together...but I finally figured it out. only cost me 3 days of my time and an unnesessary motor tear down :rolleyes:
Do you think there is anything to be gained by not installing them?
 

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The boat I have was making a grinding noise so I took it to a marina and he took the outdrive off and the metal part of the flapper fell out. The grinding noise was from the gimbal bearing, but the fact that the only thing left was the metal meant that the exhaust got so hot at one point it melted them. I would replace them or install them if missing. Sounds like insurance in my opinion. I was told that if you boat stalls while running that when you stop the surge of water behind your boat could run up you exhaust and into you engine. The pressure from the exhaust keeps them open. When it dies the close.
 
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