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Thread: homebuilt surface drive - thinking out loud.

  1. #1
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    Default homebuilt surface drive - thinking out loud.

    I have an opportunity to buy a pretty busted up - but very common - Johnson 15hp 2 cycle with a strong powerhead.

    If I can come up with an adapter tube for the carb, is there any reason I couldn't turn the motor 90 degrees to make it a horizontal output shaft and build a short tail mud motor around it?

    Just curious. Thanks.

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    Johnson like an outboard? Probably not a good Idea if so. Most surface drives are just law mower engines.mine Is a Briggs and Stratton. The main thing is it is air cooled. Not sure how your application would work, but pretty easy to rig a belt and sprockets.

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    Quote Originally Posted by Don_h View Post
    Johnson like an outboard? Probably not a good Idea if so. Most surface drives are just law mower engines.mine Is a Briggs and Stratton. The main thing is it is air cooled. Not sure how your application would work, but pretty easy to rig a belt and sprockets.
    Yup, Johnson like an outboard. I have a chance to buy a lift for an outbaord also, but i think what i really want is a short tail.

    The 4 cycle engines in the 12-20hp range make a lot more torque, but weigh a lot more than the 2 cycle engine of the same power.

    If I was really running in mud I would want the torque. What I am doing is running in shallow water. I want the power without the weight and willing to do without the torque.

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    It would depend on how the oil is moved through the motor for lubrication.
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    It will work. The lube is from premix and will get to all the important parts no matter which way you mount it. Because of the water cooling you are going to have to set up a water pump of some sort. An easier build and a lot easier to mount and hook up would be an old snowmachine air cooled engine. A one cyl would be plenty if you only need 15HP.

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    WOW...15 hp! I have a 6.5hp air cooled Honda horz shaft that I'm going to make into a long tail for my Esquif Cargo at some point. I would think the problem is getting good cooling unless the water pump can be made to work somehow. Pump is in the lower unit.

    Probably better off with an air cooled horz. shaft.
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    making a long tail a friend of mine made a long tail with a 8 HP air cooled motor for the back ent of a 19 FT grumman the bigest problem was
    it had a lot of vibration an shooked a lot . no dampining on the motor an shaft, he would tale it on the BIG SUE for about
    a 15 mile trip, did it 2 times an went to the lift with a 15 hp & 2 cycle , said it was tuff on the canoe, need lots of room to turn an not tip the rig over
    SID

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    You're right Sid, takes a fair amount of room to come about. My Honda engine is pretty smooth because I think it has a counter balancer on the crank but there certainly is a great potential for unbalance on the prop or shaft and I may try a short long tail just because of that possibility.

    I've also given some thought to using an electric trolling motor which would put the motor on the end of the shaft and only one cable on the shaft by using the shaft as the ground (neg). Problem is that most of the trolling motors use a plastic prop...not suitable for a mud/shallow water motor....just thinking out loud.
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    >>>>>>>>>>>>>>>>>>> MISTAKE SID

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    I made a longtail for my coleman sq stern using a 3hp B&S. A friend gave me a prop that had been on a 15hp longtail that was worn down to about 6". Even worn that much, it was still too much prop so I off set the shaft and geared it down with chain and sprocket. It works pretty good but you do have to be careful on turns. I would stay away from water cooled motors with anything you intend to use in really muddy or weedy water as keeping water flowing to the motor will be difficult.

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    NOW...THAT's a drag scow!!
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