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  1. #1

    Question Fitting Mercruiser Transoms

    I cut out the transom today to fit a pair of new Mercruiser Alpha 1 Gen 2 transoms. The job went well by making carefull use of the paper templates provided. The transom of my Settimo Velo (http://www.facebook.com/group.php?gid=179427293999) is of ply construction so I've sanded and sealed the end grain of the cut outs and bolt holes with a good coat of epoxy.

    Mercruiser's installation instructions do not recommend the application of any form of sealant between the outer transom and the hull. The outer transom has a deep rubber seal all the way around it, so I guess that this will be good enough to make a water tight seal against my nice flat transom when it is torqued up to the inner transom?

    Is it best practice to fit Mercruiser Transoms without sealant, or would you apply some?
    The Project: http://www.facebook.com/group.php?gid=179427293999

  2. #2
    Join Date
    Dec 2010
    Location
    Big white NE house with black shutters
    Posts
    126

    Default Re: Fitting Mercruiser Transoms

    The seal is applied dry from the manufacturer. Just be certain that you have sealed off all the holes you drilled for the bolts.

  3. #3
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,450

    Default Re: Fitting Mercruiser Transoms

    One thing you can do is, Before installing the bolts into the holes or nuts on the bolts, you can put some marine rtv on the bolt shafts/nut heads. Not a lot but enough to create a good seal when tightened. There will be some relaxation of the bolts (not much) but some and the added silicone will make sure to seal the thru holes. I agree with GotBoat, No added sealent for the large O-RING.

    Also when the time comes for setting up your shifting let us know as we have the EXACT proceedure for standard rotation anyway. Not sure about counter rotation but it can be found.

  4. #4
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    3,176

    Default Re: Fitting Mercruiser Transoms

    Before you install your used transom assemblies, replace that rubber seal that goes around. Do not reuse the old seal.

  5. #5
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,227

    Default Re: Fitting Mercruiser Transoms

    Terminology varies from one region of the planet to the next, so I'm offering a friendly FYI here, if I may;
    Transom = in his scenario; the nearly vertical "structural" component at the hull's stern area, perpendicular to the hull's length. (traverse, croisillon)
    Gimbal Housing = Merc's stern drive component that allows the mounting of the Stern Drive to the hull's Transom.
    Again..... an FYI only.
    ************************

    Settimo Velo, I just looked at your photos..... you've done some very extensive and very nice work, from the looks of it.
    Great job! I may ear mark your album and check in from time to time. Keep up the good work!

    I agree with Chris..... replace the rubber seals if these are used Gimbal Housings. That particular seal must sit "proud" of it's groove, in order to offer the correct amount of compression, once the Gimbal Housing is tightened against the Transom.

    No offense KGHOST, but I'm of the belief that silicone has little to no place in a Marine environment. Boat Life's "Life Caulk" or one of the 3M products would better suit the requirements here, IMO. The benefit being, the duration of performance, over that of silicone.

    .
    Last edited by RicardoMarine; 01-29-2011 at 09:25 AM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  6. #6

    Default Re: Fitting Mercruiser Transoms

    Thank you for all of your replies and the nice comments about my restoration work!

    They are brand new transoms so the o ring seal is perfect. The holes in the boat are drilled (as per Mercruiser spec.) 15 mm for the eight M10 studs. I could attempt to seal these 15 mm holes with caulk but just question the purpose of doing this if I do not also attempt to seal the main cutout. So, I guess the question is should apply a good underwater marine caulk to seal both the bolt holes and the cutout? These are designed to be protected from water ingress by the main o ring seal but is it common practice to trust this or to apply additional sealant inside of this - to the bolt holes and cutout?
    The Project: http://www.facebook.com/group.php?gid=179427293999

  7. #7
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,227

    Default Re: Fitting Mercruiser Transoms

    You are correct! The stud/bolt pattern is within the circle of the rubber seal.
    Intrinsically, you'd think that this would provide adequate stud/bolt sealing....... and I believe that it will!

    I have no issues with using a sealant both in the groove, and on the actual sealing gasket, of the Gimbal Housing.
    Life Caulk would be my preferrence here..... maybe 3M 4200 next.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  8. #8
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    3,176

    Default Re: Fitting Mercruiser Transoms

    Sorry, I miss read your original post. I thought they were used housings. FYI, installing them is a two person job. Have some one inside while you are on the outside watching, making sure that your new o-ring seal does not protrude from any part of the new housing while tightening. Make sure you tighten them to the correct torque.

  9. #9
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,450

    Default Re: Fitting Mercruiser Transoms

    Here is a pic showing what I was trying to explain. when drilling thru a transom for anu accessory even mounting a outboard I have ALWAYS added some caulk/Marine RTV at the locations shown. It acts like a sealing washer.

    The factory does not do this when installing a transom but it can not hurt.......

    Attachment 1642

  10. #10

    Default Re: Fitting Mercruiser Transoms

    I see what you mean. The job is now done and that is just how I sealed up the stud holes through the transom. I will post some pictures on my Facebook Group at the weekend. Thank you all for your help.
    The Project: http://www.facebook.com/group.php?gid=179427293999

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