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Better exhaust flappers?

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  • Better exhaust flappers?

    Had a not-fun event last weekend. Got water up the exhaust into my port engine port manifold (dual exhaust/dual mufflers on our 28 with twin 350's). We were on a buoy at blake island for ~2 hours having lunch and the engine just made a clunk noise when I went to start it. Talk about a sinking feeling...

    Took the plugs out and cleared the water, engine seems to run fine and after a very long warm up I ran it hard for about an hour to burn any seawater out. Crossing my fingers that I got lucky, no water in the oil or bad noises. Had a little more trouble syncing the engines on plane, seemed to want to hunt back and forth on the sync gage-I'm thinking this was just me being more critical of linkage slop though. Plan on changing oil and spark plugs just because, and I pulled the plugs and fogged the cylinders when we got back to the slip. After it sat for a while I checked for water and it was bone dry so that should rule out a manifold leak.

    That out of the way... how do I keep this from happening again?! My exhaust flappers don't actively close at rest-they're about 3" open at the bottom, is there a better brand that stays closed at rest? We had a few good pitches when the boat wasn't level(4 adults on one side) but it doesn't seem like we should need to be that concerned with keeping the boat level.

  • #2
    I dont remember if you have gears or outdrives...? You can get taller risers or extensions if you have room under the floor.
    1982 2580 "HI-BOY " IN 2 DEEP 5.7LX ALPHA

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    • #3
      V-drives. I did think about risers but I'm not sure I have enough room to go up to call it "fixed" with the amount of water I had. There might be 4" of space and the floors are pretty high above water level to start with.

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      • #4
        Flappers should hang down when engines are off. We’re you getting some wave action up against the transom? My 28 has two exhausts, both protected with rubber flappers. That rubber hardens over time and will not lose the exhaust pipes, I would replace the flappers before moving the risers,
        The cruise liner QE2 moves only six inches for each gallon of diesel fuel that it burns.

        1982 28' Long Cabin "Molly Brown" sweating through a long hot summer. Massive California forest fires fill our sky with smoke. SUP paddlers and kayakers transit the harbor with abandon, thinking they have the right of way over all boats.

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        • #5
          I run 4 exhaust thru hulls with the rubber flappers and have never had an issue. My flappers close to within about 3/8" to 1/2" on the exhaust exit. Any wave action closes them completely.
          "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

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          • #6
            Originally posted by Bill V View Post
            I run 4 exhaust thru hulls with the rubber flappers and have never had an issue. My flappers close to within about 3/8" to 1/2" on the exhaust exit. Any wave action closes them completely.
            I have the same setup as you Bill with the exception that my pipes a smaller and I have mufflers-I would think that would help prevent slosh. Sounds like the flappers are just worn out and I discovered it the hard way.

            Bill what brand are yours? generic sea choice/etc or something better?

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            • #7
              Sierra brand, all new when I reported 2 years ago
              "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

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              • #8
                thanks Bill, I'll get some sierras

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                • #9
                  Might retrofit these in this winter and keep the external flaps as well.

                  Looks pretty simple to retrofit an internal flapper similar to what I/O boats have from the factory. Just pull the flex exhaust hose from the hull fittings and drill a couple holes inside, then the holes are covered by the flex exhaust hose when reinstalled.

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                  • #10
                    Based on my experience and the number of 28's running V8's with rubber flappers I suspect these to be band aides to the real problem, exhaust design and installation.
                    "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

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                    • #11
                      Do you mean specific to my boat- I would think that with mufflers mine would be slightly better off risk wise?

                      Other than taller risers do you have a suggestion for how I could improve my exhaust installation?

                      I cant find a current picture of the redone exhaust supports but this is what I have x’s 4.

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                      • #12
                        Your exhaust is full of water until it starts up thru the elbow. Lots of water already near the riser and wouldn’t take much to push over the top.
                        "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

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                        • #13
                          But how is that different than any other 28- don’t they all have similar underwater exhaust piping that stays flooded at rest?

                          It sounded like you suggested the design of my exhaust might have a flaw different than others, or were you saying that many 28’s are at risk and those flappers are just very important?

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                          • #14
                            None of the factory V8's with V-drives have more then 6-10" of exhaust full of water and that is for each engine as they have a "single" exhaust. The exhaust turns up almost immediately after coming thru transom. On mine I start up 6" after entering thru transom. Yours has 20-24" full of water.
                            "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

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                            • #15
                              I see boat dollars in my future... did some research on my mufflers and it turns out they are intended for above waterline use. 3" dynamax centek mufflers (1005001) are what I have. May put a call in to Centek but sounds like I'll be getting some new exhaust this winter.

                              Can you show/describe what yours looks like Bill? I might try to put the mufflers right behind the risers and see if the leftover space allows room for a wire reinforced exhaust hose to bend down to the transom. That would get them above waterline and "hold" less water in the exhaust. Now that I've had mufflers I've gotten used to it being reasonably quiet on plane.

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