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  1. #1
    Seaman
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    Default swapping from OMC 800 to Mercruiser

    If I change my I/O from it's present OMC 800 to a Mercruiser system, which Mercruiser will work on my particular boat? I have a 1984 Proline 23' walkaround with a OMC 3.8, 185 hp stringer. I don't need more power, so I'd be satisfied with a 4.3. I also want something that's as simple and reliable as possible, without breaking the bank. I am not sure which Mercruiser type, the Alpha One, Gen two, or otherwise, would suit my purposes.
    I've been told that instead of rebuilding the part of my transom where my current transom seal goes, I can attach a plate to cover it and mount the Mercruiser outdrive to that. Are there any pros and cons of going that route? I don't mind doing the rebuild, I can do anything and have a very solid transom to start with.
    Assuming that I go ahead with the swap, what year 4.3 should I be looking for, and EFI or carbureted?

  2. #2
    Moderator Bondo's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    Well,...........

    "what year 4.3 should I be looking for, and EFI or carbureted? "

    Any of them are Fine,........
    Newer is Always Better,..And It'll be Pretty New,+ Expensive for the EFIs........

    "the Alpha One, Gen two, or otherwise,"

    Either of these would be a Great Choice,.........
    Bravos are Expensive,+ Harder to find,........ As well as Over-kill for what you want......
    I'd try to stay away from the old Pre-Alphas,..... Also known as Mod.1s......
    There are also a few others,.... But the Alphas will be The drive for you......

    "I can attach a plate to cover it and mount the Mercruiser outdrive to that."

    Nope,......... Won't Work,...... Don't even Think about it..........
    Mercruisers Need 2" of transom Thickness,...... Total.....
    Just Epoxy in a few pieces of Plywood,+ be Done with it,..... It'll be Plenty Strong,+ Last Forever......


    I've been involved with Several of these Same Refits,..............
    There's Really only 2 ways to Go,.............
    Either go out+ Buy a Donor Boat,..... 1 that has the Motor,+ Drive You want,......
    Then Bone it Out,.... Junk It.......
    That way you HAVE All the little pieces that make Everything fit together,..... Otherwise it'll Break the Bank in No Time......
    Or,............
    If your Pockets reach your ankles,.............
    Buy Everything Brand New,+ Have SomeBody Else put it together For you......................

    Good Luck..........
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
    Seaman
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    Default Re: swapping from OMC 800 to Mercruiser

    Thanks. I will most likely be shopping around for a donor boat.

  4. #4
    Seaman
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    Default Re: swapping from OMC 800 to Mercruiser

    I see that quite a few people have looked at this post. Are there others out there that have done this conversion with ideas about it?

  5. #5
    Supreme Mariner Haut Medoc's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    Bondo prettty much has it covered.....
    I can't think of anything much to add....
    Other than make sure this is the boat you want to keep.....
    I think you will be hard pressed to find a donor that will be as cheap as you would like.....
    Then, you still have the task of installing the new package.....
    IMHO, you would be better off looking for a newer boat with a Merc. or Volvo package, keeping in mind that Merc.'s are much more plentiful with regard to spare parts & service as well......
    If you can find a donor/ new boat with a closed cooling system, better yet!
    & Try to stay away from the one piece manifold/riser set-ups.......Good Luck!........JK
    Disclaimer!: In my inexpert opinion......

  6. #6
    Lieutenant Commander mkast's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    I've noticed complete power packages sold on EBay, 5.7 small block with an Alpha 1, for as little as $2000.
    From Mercruiser:
    Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

  7. #7
    DJ
    Guest

    Default Re: swapping from OMC 800 to Mercruiser

    You can buy complete stern drive packages for similar prices close to similarly sized outboards. The I/O's are actually a little cheaper.

    See link below.


    http://www.dougrussell.com/Products/...=47&Category=6


    The folks at Doug Russel are very helpful.

  8. #8
    Moderator Bondo's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    My Point above is that IF you buy a Repower Package like the 1s above,.........................

    You'll be Short Abunch of Little Pieces,................
    The Controller,.........
    Wiring for the Boat-side of Things,......
    And Alot more Stuff...........
    And,....
    Those Little Pieces will Drive the Price Up about what you Paid for the Package,..... Or More..........

    With a Donor Boat,........
    You've Got it All...................
    Any Grease is Better,..... Than No Grease at All.......

  9. #9
    Lieutenant Commander
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    Default Re: swapping from OMC 800 to Mercruiser

    What's up with the stringer? Wouldn't it be much cheaper to find used stringer parts?

    Sounds like a wack of dough and time otherwise.

  10. #10
    Seaman
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    Default Re: swapping from OMC 800 to Mercruiser

    The stringer system is already 20 yrs old and some parts are next to impossible to find. For instance, last year I had to replace the distributor. That part was made by Prestolite, no longer in business. After much searching I bought the only one I could find on Ebay. Same thing for the trim pump and motor mounts.
    I really like the boat, which is in good shape and gives a really good ride, so I'll probably keep it for a few more years. I just need a good, reliable drive system that I can find parts for when needed.

  11. #11
    Senior Chief Petty Officer
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    Default Re: swapping from OMC 800 to Mercruiser

    Parts are not that hard to find. Doug Russell has just about every part. Even the motor mounts and trim cylinders. They actually have brand new trim cylinders in stock. Of course they are very expensive but you could find it. Surprised you have trouble finding a trim pump. They're all over the place if you search the internet. You probably could have swapped out the distributor for a Mallory. I'm in the same boat (no pun intended) as you. You can repower with a brand new OMC 800. They are available, or you could just get a rebuilt one. My case is in good shape and when it comes to rebuild, I am just going to take it off and haul it up to the shop. Got to be cheaper this way than buying one from dougrussell.com. You could always plug the hole and throw an outboard on back.

  12. #12
    Seaman Apprentice
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    Default Re: swapping from OMC 800 to Mercruiser

    Would Mercruiser part no. 827691A1, transom adapter plate,
    work in this application?

  13. #13
    Moderator Bondo's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    Quote Originally Posted by JIm
    Would Mercruiser part no. 827691A1, transom adapter plate,
    work in this application?
    Without a Picture,........ That # means Nothing to Me,........

    Maybe somebody's got a Look-up on it............
    Any Grease is Better,..... Than No Grease at All.......

  14. #14
    Seaman
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    Default Re: swapping from OMC 800 to Mercruiser

    I looked up the part at a couple of web sites and although I couldn't find a pic of the plate I did find out that the price is around $800 from BAM in Florida. I don't know what you get for that, but it sounds kind of pricey for an adapter plate.

  15. #15
    Moderator Bondo's Avatar
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    Default Re: swapping from OMC 800 to Mercruiser

    Personally,.......... I use Epoxy,+ Plywood........

    The Only "Adapter Plate" I've ever seen,.....
    Allowed a Merc. to be bolted into an old Volvo cutout...........

    It's another of those "Little Pieces" you get from a Donor Boat,........
    I cut out the Merc. Hole from the outer transom of the Donor,+ Trim it to Fit the Old Hole..........
    Once you establish the Position of the New Hole,.......
    It's just a matter of Grinding, Glueing, Grinding, Filling, Sanding, Flairing,+ Sanding,...........Alot.......
    Any Grease is Better,..... Than No Grease at All.......

  16. #16
    Seaman Apprentice
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    Default Re: swapping from OMC 800 to Mercruiser

    It can be viewed at www.mercurypartsexpress.com.
    Click on "Parts for Mercury Marine Products" and enter part
    no. 827691A1. Shows to be about $1000.00 but if you
    Google the part no. it can be found around $750.00.
    A long long time ago, Don S. posted a picture of it but I
    have not figuired how to do that.

  17. #17

    Default Re: swapping from OMC 800 to Mercruiser

    the alpha is a good dependable drive. will work on anything up to 200 to 250 hp. the bravos are a bit over kill for your application, and would amount to some more expensive dead weight.

    im a little peeved at mercuiser EFI systems right now, so take what im about to say in that context, and solicit openions from other people. EFI sucks for boats. when it works, it works awsome. instant starting, more power, better fuel effiency. when it is not working well, it is usually not working at all. a sensor, voltage drop, relay, small leak, any little thing and you will be looking for a tow home.

    a carburator, while not as effecient, and a bit less power, will get you home weather it is working perfectly, leaking, sucking air, partially clogged, whatever. and when it does go down, getting it fixed or replaced wont put you in the poor house.

    simpler is better for boats IMO. you could have a dead battery, and throw your alternator belt and a carberator will not know the differance. again, im just a bit jaded with EFI at the moment.,

  18. #18
    Supreme Mariner
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    Default Re: swapping from OMC 800 to Mercruiser

    biggest issue you have is transom strength.
    by the mid 70's most stern drive hulls could be had with merc or omc stringer. so by then most had 2" transoms.
    some did not.
    the stringer drive transmits fwd thrust to the hull stringers the mercs transmitted fwd thrust to the transom.
    we repowered a 72 hull from omc stringer to 5.7 merc EFI with a genII drive,
    total cost was about 20K. would have been more but no transom mods other than fillling the hole were required.
    once you remove all the OMC stuff take the boat to a glass shop with the template for the cutout and tell them to call you when its done. after that its just a time consuming job of installing the parts.
    in this area the transom will set you back about 700 dollars. but as Bond-o and others have pointed out, its not hard just takes time and can be messy.
    our shop is not set up for glasss work and I quit doing it years ago due to safty concerns.
    gotta watch out for fire marshall Bill ya know.

    no tech questions by PM, they wont get answered.
    you have to be trusted by the people that you lie to .

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