Manifolds and Risers

Discussion in 'Sport Boats' started by PsyGrad, Oct 17, 2019.

  1. PsyGrad

    PsyGrad New Member

    May 30, 2007
    Long Island
    215 Express Cruiser
    5.0L MPI
    I have a 2001 SeaRay Express Cruiser. Engine replaced in 2007 with 5.0 MPI Mercruiser crate engine. The manifolds and risers have not been changed since. Boat is trailered and gets flushed with fresh water upon each use. Is the replacement of manifolds and risers a DIY? I have read up on some of the posts on the subject, seems like the concern is the bolt snapping. How do I prevent this, and if I can, what are the remedies?
  2. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Yes,it’s definitely a DIY project.

    As far as breaking a bolt, I would get the engine good and warm first. The heat will help free up any rust. Use a long handle ratchet or breaker bar, but don’t put too much force into it.

    You could use a torque wrench to loosen it too. They are only torqued to about 35 ft/lbs when installed new, so set it for a slightly higher number and stop if it clicks.
    Chris-380 likes this.
  3. LG111

    LG111 Active Member

    Jan 4, 2015
    44 Sedan Bridge - 06 Black Hull
    Spray penetrating oil on the bolts 24hours prior. That will help. Heat works but the manifold will get to hot to touch near the bottom at the bolts.
    OllieC likes this.
  4. 370Dancer

    370Dancer Well-Known Member

    Oct 2, 2006
    Florida - Alabama
    1998 370 Sundancer
    380hp MAG MPI Gen VI with V drives
    Even Mercruiser OEM manifolds and risers are made of iron. It's not the water flowing, but more the air corroding the moist cast when put up. If you boat in Salt, it will corrode faster.
    It is simple enough to do a visual check by first observing the outside of the joints to the engine, and the riser. If they are showing leaks, so is the inside. Chances are you have "dry joints" where the water is routed through external hoses from the manifold to the spacer if used, and then to the riser. This helps eliminate the issues of water leaking at these mechanical joints. It does not address water jacket to exhaust chamber leakage though because of corrosion. You should be able to remove the exhaust hose from the riser, and note that there is little to no condensation in the center exhaust port. May be wishful thinking, because it is a dark, damp place after you have flushed. If that's wet, then you will want to remove the riser to check the exhaust chamber's vertical walls. Water or moisture there is what leads to ingestion by the cylinders via the exhaust valves. Water doesn't compress, and bang, your engine will work very hard to make it compress.
    Most people replace exhaust components as a preventative measure rather than a reaction. Usually if you are replacing because of a leak, then there may be other damage already done.
  5. SloBurn

    SloBurn Active Member

    May 30, 2013
    Greenwood Lake, NY
    1994 270 Sundancer. 7.4L Merc. Tow with a 2006 Dodge RAM Hemi
    340 HP Merc 454 c.i.
    Yes, I have done this several times. I even broke a bolt, not a big deal as it came out with Vise Grips once manifold was off. NOTE gasket and block off plate position before removing them.
  6. PsyGrad

    PsyGrad New Member

    May 30, 2007
    Long Island
    215 Express Cruiser
    5.0L MPI
    Thanks everyone!

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