outboard to four stroke conversion

Discussion in 'DIY Marinizing' started by essenmein, Aug 8, 2016.

  1. essenmein
    Joined: Dec 2014
    Posts: 40
    Likes: 10, Points: 0, Legacy Rep: 75
    Location: halifax

    essenmein Junior Member

    I had purchased an old fisherman 5.5 evinrude for my little boat project that had two major issues. One I could never get it running right with all the idle/high speed jet settings, and the oil slick it would leave where ever it went I'm sure is a federal offence somewhere.

    I also had an old pressure washer with a dead pump but perfectly good 5hp brigs motor sitting there begging to be used in something.

    So after a beer or three I decided I should mount up the four stroke to the evinrude lower leg.

    After some quick checks, like does the motor spin the same direction, I tore the old smoker off the outboard and had a think about how to mate the two shafts.

    I had the machinist guy at work make me an adaptor to go from the ~10mm splined shaft of the outboard lower to the 3/4" keyed shaft to mount a lovejoy style coupling.

    The adaptor is nothing more than a bit of 3/4 key shaft with a hole put in the middle that was a tight slip fit over the splines which I would then weld on, fillet around the bottom where it goes down to the gear box and a healthy plug weld to fill in the top.

    Then built a simple steel adaptor plate with holes in the same spot the original motor mounted to the lower leg, and some tabs to hold the pressure wash motor at the right height to allow the coupler to fit in there.

    I removed the internals in the leg except the drive shaft and the gear shifter, water pump impeller etc are all gone.

    Bolt the whole thing up and line up the coupling.

    I was expecting a fight to get it to run smoothly, so I was a little surprised when I first fired it up that it was perfect. In hind sight the motor shaft forces the alignment so it was always going to be fine.

    Unfortunately I only took some photos in the process.

    Now it just needs some splash guards, as I m sure salt water will make its life quite short.

    The evinrude max rpm was 4 or 5k, can't remember the exact number, and the briggs is 3600rpm, so its not going to hit the same speeds as the original motor, but no more oil slicks and fluffing about with all the mixtures to get it working right.

    Its had a couple of runs now and works nicely, also way easier on gas!

    Just need to take it apart for cleaning and coat of paint.

    Attached Files:

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