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outdrive shell/casing

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  • outdrive shell/casing

    I have a 1989 Fours Winns 180 Horizon with a 4.3 L cobra outdrive. Question I have is not mechanical but more cosmetic. The paint is coming off really bad. I keep the boat in the river all summer, pull it out about mid season to clean the hull. Last year I noticed alot of electrolysis on the out drive when I took the boat out mid season I powered washed the outdrive it cleaned up alright but I know that wouldn't make any difference. A friend of mine had his outdrive repainted but said he wasted his money maybe who ever did it, didn't do a good job. Anyway, when I took it out this year it was alot worse, about all the paint is gone. Covered with electrolysis like a fast spreading cancer. The aluminum is starting to pit. First question what causes the electrolysis to be so bad, is there anyway to prevent it. Second, is it a waste of time to have the outdrive repainted. I would almost be tempted to buy new shell for upper and lower unit, but with it being a omc cobra that would probably be a waste of time, probably impossible.
    Thanks for time and imput, Ron

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    Re: outdrive shell/casing

    If you use a factory repainting procedure it will be as good as new. Sand or bead blast all the corrosion off it, use an aluminum prep then a conversion coating, then epoxy prime it, and finally paint it with a catalyzed (2-part) paint. Here's the Mercruiser data, the OMC will be the same just choose your final paint color instead of the black. And get the smallest quantities possible, a pint of paint will probably do 3 outdrives!:


    Is there a factory authorized repainting procedure for my sterndrive?
    Yes, MerCruiser has a refinishing procedure available. For best results we recommend this procedure be performed professionally.

    Refinishing procedure:

    This procedure should be used in refinishing MerCruiser sterndrives and transom plates. This procedure will provide the most durable paint system available in the field. The listed materials should be purchased from a local DITZLER AUTOMOTIVE finish supply outlet. The minimum packaged quantity of each material shown is sufficient to refinish several sterndrives and transom assemblies.

    1 QT. DX-533 Alumiprep #33 metal preparation
    1 QT. DX-503 Alodine #1201 conversion coating
    1 QT. DP-40 Non sanding Epoxy Primer zinc chromate primer
    1 QT. DP-401 Catalyst for DP-40
    1 QT. DAR-9000 Acrylic Enamel-black topcoat
    1 Pt. DXR-80 Delthane Ultra-additive for acrylic enamel
    1 QT. DTR-602 Acrylic Enamel Reducer-temperature range 70-90 degree F.


    1. Scuff sand to remove all blistered paint and roughen factory finish. Remove sanding dust.
    2. Follow manufacturer's recommendations and instructions on the individual containers.
    3. Apply DX-533 (Alumiprep #33) to clean and condition the aluminum.
    4. Apply DX-503 (Alodine #1201) brush on chemical conversion coating for aluminum.
    5. The DP-40 (Epoxy Chromate Primer) mixed with DP-401 Catalyst can now be applied. A .75 mil film build is recommended.
    NOTE: Allow 30 minute induction period for permeation of the epoxy chromate primer and the catalyst prior to application.
    6. The topcoat consists of DAR-9000 Acrylic Enamel Black and the DXR-80 Delthane Ultra additive, and DTR-602 Reducer. It is a polyurethane acrylic enamel system which provides fast drying, durability, high resistance to corrosion and good color and gloss retention.
    7. The type of spray gun used will determine the proper reduction ratio IMPORTANT: DO NOT use any type of aerosol spray paints, as the paint will not properly adhere to the surface, nor will the coating be sufficiently thick to resist future paint blistering.


    From my experience you're pretty much wasting your time with the paint cans except for very minor touch-up. Make sure you have fresh zincs and you should be good with the corrosion. Once the aluminum on the housing is exposed it just accelerates the corrosion process.

    I did mine about a month and a half ago and it still looks brand new. Only thing I did different was use a urethane instead of an enamel. There's some pics of the top plate on this thread:

    Last edited by 45Auto; September 30th, 2007, 07:44 PM. Reason: added old thread
    Any opinions expressed above are worth exactly what you paid for them!