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Manifolds and Risers - semi stupid question...

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    Manifolds and Risers - semi stupid question...

    Merc 7.4 - can I change the Risers and Manis while the boat is in the water or is this a job best performed in a yard?
    1998 Bayliner 2858
    7.4L MPI / Bravo III
    Harbour Village Marina - Kenmore WA

    #2
    I always do it with boat in water, no problem. On reassembly, I usually put spacers on manifolds first as easier to get proper torque, and use studs to hold manifolds in place while reinserting bolts to heads.

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      #3
      Thanks - looks like its time to get busy!
      1998 Bayliner 2858
      7.4L MPI / Bravo III
      Harbour Village Marina - Kenmore WA

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        #4
        Plus one on using studs to hold the manifold and gasket in place so you can get the manifold bolts started. It’s also a great tome to replace the spark plugs and wires and pay lots of attention to the hose clamps. The new embossed ones are more resistant to cracking. Also, I’ve learned that hose clamps can actually be too tight causing internal damage to the hose. https://www.boatus.com/seaworthy/mag...hose-clamp.asp Some of it is counterintuitive until you read the whole explanation. I had to read it three times.
        P/C Pete
        Edmonds Yacht Club (Commodore 1993)
        1988 3818 "GLAUBEN”
        Hino EH700 175 Onan MDKD Genset
        MMSI 367770440

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          #5
          Well....yes it can be done...however, depending how high up the water will be in the Y pipe, it is possible for water to spill over into the bilge, if someone kicks up a wake near where the boat's docked or moored. So...being a cautions kinda guy I'd measure the diameter of the Y pipe and fab up a rubber cover of some sort to cover them while you get the manifolds installed. And yeas the stud approach to making it easy to line up the gaskets & heavy manifolds works great...take a manifold bolt to a hardware store, get 2 longer bolts, cut the heads off and then cut a slot in the end of the stud, this is so you can turn it out with a screwdriver. I did this when I did my 4.3 exhaust a few years ago...

          BTW, you can use the same trick for the bolts holding the elbows onto the manifolds, just get 2 longer bolts, cut the heads off, make a slot in the end for a screwdriver, this especially helps if you use sealer on the manifold to elbow gaskets, it keeps them from sliding around while you line up the elbows, just drop them down over the 2 long studs, start the other two bolts, remove the studs and install the last 2 bolts. Done! And as a habit I always use a thread chaser in the cyl head holes and the manifold holes for the bolts, to make sure the bolts will thread in well and the torque setting will be more accurate that way.
          Click image for larger version  Name:	IMG_2270.JPG Views:	0 Size:	2.57 MB ID:	600313
          88 Four Winns 200 Horizon 4.3 OMC
          98 Jeep Grand Cherokee 4.0/Selectrac
          07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

          Long Island Sound Region

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            #6
            Agree with 88, find out where the static waterline is in relation to the top of your Y pipe on your specific boat.
            BTW the Mercruiser Y pipe is oval at the top. You could re install the intermediate elbows on the Y pipe to gain a substantial increase in elevation while you swap the exhaust manifolds/spacers/elbows.
            Dave
            Edmonds, WA
            "THE FIX"
            '93 2556
            Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

            The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
            Misc. projects thread
            https://www.baylinerownersclub.org/f...56-gctid789773

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              #7
              Plumbers plugs (3 & 4”). Work well. I carry a couple just in case. You stick it in the pipe and torque it down to seal it.
              Glen Sherwood
              1987 3270 twin 305’s
              Coupeville, WA

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