Adapting CD Magneto To Points Style Block

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  • Mumbles
    Mumbles
    Canada Member - 2 Years
    Replies: 3966
    Topics: 401
    #173279

    After assembling a replacement powerhead for a ’77 six horse I’m building, I realized the block had the smaller bearing boss on top as found on the ’76 and earlier motors which used the universal points style magneto. Wanting to keep it correct, the choices were to find and rebuild a ’77 – ’79 block with the larger boss or figure out a way to adapt a CD magneto to the freshly rebuilt RPH powerhead I had just finished. I chose the second way.

    After comparing both types of blocks and doing some careful measuring, it struck me that it just might be possible with a custom bushing. First, I turned down some 2 1/2″ aluminum round bar to size and bored it out for a good fit over the small bearing boss. Three 8/32″ stainless set screws evenly spaced around the base will hold it in place.

    Here you can see the difference between a points mag bearing boss on the left and a CD one on the right.

    The new bushing fit perfectly on the fresh powerhead but four 1/2″ spacers were needed to keep the mag plate at the correct height. The heads of the new retaining screws needed to be thinned down a bit to for clearance between them and the mag plate.

    This fix should work as the motor turns over freely with no signs of interference or binding anywhere. I know it would have been a lot quicker and easier to have used a points magneto but like I said, I want this one to be correct!

    • This topic was modified 4 days, 20 hours ago by Mumbles Mumbles.
    • This topic was modified 4 days, 20 hours ago by Mumbles Mumbles.
    • This topic was modified 4 days, 20 hours ago by Mumbles Mumbles.
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    Mumbles
    Mumbles
    Canada Member - 2 Years
    Replies: 3966
    Topics: 401
    #173287

    Some more photos.

    • This reply was modified 4 days, 20 hours ago by Mumbles Mumbles.
    • This reply was modified 4 days, 20 hours ago by Mumbles Mumbles.
    • This reply was modified 4 days, 20 hours ago by Mumbles Mumbles.
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    bobw
    bobw
    US Member - 1 Year
    Replies: 427
    Topics: 23
    #173300

    Great work!

    Bob

    1954 Johnson CD-11
    1958 Johnson QD-19
    1956 Johnson RD-18

    Buccaneer
    Buccaneer
    US Member - 1 Year
    Replies: 2874
    Topics: 802
    #173301

    Great Work-around! The lathe, greatest invention since the wheel!

    Prepare to be boarded!

    Avatar
    fleetwin
    US Member - 2 Years
    Replies: 2531
    Topics: 29
    #173403

    Boy, that is beautiful engineering/machining work indeed….The OEM retaining screws for that retainer plate are lower and won’t interfere….
    http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1977&hp=6&model=6704M&manufacturer=Evinrude&section=Magneto
    #41 304442
    Can’t wait to hear this little gem run, what happened to the original powerhead/crankcase??

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