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Replacing risers and manifolds

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  • Replacing risers and manifolds

    So I'm thinking about replacing my risers and manifolds. Question is should I do both or just the risers. I believe these are original. And when I look at riser gaskets it says most normal are two slots and two pin holes or I could select 4 slotted gaskets. Any opinions on this. Also this is a 89 mercruiser 305. 5.0lx

  • #2
    You may want to inspect them first for corrosion etc. -- if they are freshwater only they could still have life left on them.

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    • #3
      Do you have any signs of them leaking at the gasket between the manifold and the exhaust elbow? If so then for sure an inspection is warranted. You want to see how much flaking rust there is inside the cooling passages, is there any rust in the exhaust gas passage (sign of water leaking inside) and if the sealing surfaces are still good or getting eroded. In salt water we have to replace them about every 5-7 years. Freshwater they can last much longer but that's an 89, 30 years is a long time.
      1988 Four Winns 200 Horizon
      4.3 OMC Cobra

      98 Jeep Grand Cherokee 4.0 Selectrac
      07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

      "While air doesn't freeze....rust never sleeps"

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      • #4
        Ok fellas, pulled risers and manifolds and to my surprise at least to me they didnt look to bad. Reason I pulled port side started to leak between riser and manifold. Anyways what do you guys think. Should I replace or should I maybe take to machine shop and have surfaces trued up and run. Can you tell if these are original. Also I need to replace exhaust flappers. Port missing starboard good. Is this anything to be concerned with. Should i try to fish it out of there

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        • #5
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          • #6
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            • #7
              First thing I notice is that your have the old style shutters... They need to be changed...

              http://forums.iboats.com/forum/engin...ters-explained

              As for the one that's missing, you need to pull the drive and start looking for it. It could be jammed in the bottom of the Y-pipe, lodged in the drive somewhere, or has traveled all the way through the drive... Only when you KNOW it's not jammed somewhere should you start putting things back together.

              Chris.......
              Last edited by achris; January 7th, 2019, 12:59 AM.
              xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
              The world takes on a whole new perspective when viewed from 100’ below.
              1972 Bertram ‘Bahia Mar’ 20
              2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
              (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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              • #8
                Yeah I'm gonna work at getting that out of there. Where do they mostly end up at. Can you use a magnet to get them or how do you do it. I have a friend that owns a scope I reckon I could run through it. Also could you send me the link chris for the new style flappers I need. I believe my pipe is the 4 inch oval but I'll double check. Also could that flapper plug off that exhaust port. Read your water shutter post and seen bow it wore a hole in the pipe. Thanks man

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                • #9
                  Originally posted by midnightrider1818 View Post
                  Yeah I'm gonna work at getting that out of there. Where do they mostly end up at.
                  Jammed in the bottom of the Y-pipe, or caught up on the upper shift shaft in the bell housing, or lodged in the bearing carrier in the lower housing, or shot straight out... That's what you need to determine... Pull the drive and have a look..If it's not there, start looking down the Y-pipe... You need to be SURE it's not there...

                  Originally posted by midnightrider1818 View Post
                  Can you use a magnet to get them or how do you do it.
                  They're stainless. No a magnet won't help you.

                  Originally posted by midnightrider1818 View Post
                  I have a friend WHO owns a scope I reckon I could run through it.
                  That would help..

                  Originally posted by midnightrider1818 View Post
                  Also could you send me the link chris for the new style flappers I need. I believe my pipe is the 4 inch oval but I'll double check.
                  Part numbers are in the document I posted the link to in my last post.

                  Originally posted by midnightrider1818 View Post
                  Also could that flapper plug off that exhaust port.
                  Possible, but unlikely. The exhaust gas flow would flip it round.

                  Originally posted by midnightrider1818 View Post
                  Read your water shutter post and seen bow it wore a hole in the pipe. Thanks man
                  It did... When I was 25 nautical miles out to sea!

                  Chris......
                  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                  The world takes on a whole new perspective when viewed from 100’ below.
                  1972 Bertram ‘Bahia Mar’ 20
                  2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                  (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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                  • #10
                    Well pulled drive found no remnants of shutter. Did not see it stuck in the y pipe at the bottom but I'll run a scope through just to be sure. Went ahead and ordered a new set of risers and manifolds. I bought sierra. What do you guys think about this kit. Read that you wanna use the metal gaskets with graphite in them between the manifold and risers. Anyways this is the kit I bought.

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                    • #11
                      https://nuwavemarine.com/sierra-merc...caAtSgEALw_wcB

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                      • #12
                        I followed your post and learned that I need my shutters replaced too. Thanks achris . If the elbows look ok, can just the manifolds be replaced? I have one that was welded and don't trust anymore. Are the original risers compatible with the aftermarket sierra brand? Didn't mean to hijack this one but after I saw the riser and manifold replacement thread I thought it may be answered here
                        1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                        https://forums.iboats.com/forum/engi...4-3-block-swap

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                        • #13
                          Originally posted by Chris51280 View Post
                          I followed your post and learned that I need my shutters replaced too. Thanks achris . If the elbows look ok, can just the manifolds be replaced? I have one that was welded and don't trust anymore. Are the original risers compatible with the aftermarket sierra brand? Didn't mean to hijack this one but after I saw the riser and manifold replacement thread I thought it may be answered here
                          Yes, within the 'series' all parts are interchangeable. You can use Sierra manifolds with Merc elbows. But if you are going that far, the elbows are likely close to needing to be replaced anyway, why not jump all the way to dry joints?

                          Dry joint elbows and manifolds are plenty better than the 'wet-joint'... And some of the aftermarket makers are now doing them. I know HGE are...

                          Seriously, look at dry joint....

                          Chris.....
                          xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                          The world takes on a whole new perspective when viewed from 100’ below.
                          1972 Bertram ‘Bahia Mar’ 20
                          2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                          (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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                          • #14
                            You can take wet joint risers and convert them over to dry joint. What all do you need to do to convert over to that.

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                            • #15
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                              Ok update everybody keeping with this thread. Achris was right flappers were stuck in the tube about 2 feet down probably. Was able to fish them out with a wire and a scope. Took about 45 min with these tools. Nice thing was I was able to pull em up side by side and the exhaust kind of held them so they wouldnt slide back down. Anyways here they are. The metal rod and looks like a o ring are still down there but mo way of getting them they will just have to stay. Tried about a 1 hr on them and was afraid I was gonna scratch the scope so called it quits on those. They will have to stay

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