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Briggs & Stratton Lawnmower/Go Cart Engine to Power a Boat

I've heard of people mounting small (5 hp or so) Briggs engines in boats to power them. I have a couple of warn out 2-stroke outboards, but they are smelly, smoky, and unreliable. Does anyone know the best way to mount a Briggs (or Tecumseh, Robin, etc) as an inboard? I know there'd have to be shafts and seals, but I'm kind of looking for ideas before I start cutting on the old flatbottom. I have a couple of vertical shaft motors, and one good horizontal.

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You could do it, using a sealed shaft and bearing, but it mightn't be the best idea, you'd still risk buggering the hull. You could take the transmission axles of an outboard, run the engine from inside the boat by meshing two transoms together to make a big upside down U what would be simpler though is to simply mount it like an outboard or if you prefer fixed prop boating you can mount it permanently at the back like an outboard that doesn't turn, it's just easier and a lot less risky than attacking the hull, unless you find a scrapper with the transmission shafts in place, take the bearing and seal assembly and seal it in to your boat...
skunkbait (author)  killerjackalope8 years ago
I may go with the outboard route. Everyone seems to be against running it THROUGH the transom. The are probably right. I'd hate to ruin a good boat on this project.
Actually if the transom is flat and not made of any really exotic materials you could just risk it, it would be a cooler project, it wouldn't be any harder to get the parts, or if the mood struck you make them... I have seen boats with an outboard style assembly that goes through the bottom spine, for deeper water, they handle nicely, because the thrust is a bit further forward you can turn in your own length...
skunkbait (author)  killerjackalope8 years ago
Transom's flat and made of aluminum. I could patch any unwanted holes pretty easily. I could run it a foot out the back so it sat down in the water. A rudder for directional control wold work once I was up to speed. I also have a trolling motor I could steer with, even if the main prop is fixed.
. IIRC, most inboard designs go through the hull, not the transom. I/O's go through the transom to a "lower unit." . If you go through the transom with a straight shaft, it seems to me that you will have to put the prop so far behind the boat (to get it in the water) that you will introduce all sorts of steering and stability problems (you'll have a lot of leverage). You will also need to mount the engine at an angle, which may (or may not) present a lubrication problem. . But if you can weld Al, then none of that should be a big problem to fab or repair.
skunkbait (author)  NachoMahma8 years ago
I'll look into that. I gues mine would be more I/O. It just seems like, once it was done properly, it sure would be nice to run the thing on a cheap, non-smelly, (reasonably) quiet engine that I can actually repair while sitting on the river-bank. I could even replace it with a brand new one for like $275. A LOT cheaper than a regular boat motor.
My dad made a fanboat out of a 250cc bike engine, from his still in use bike, he got a spare prop from a plane... Motorbike engines aren't half bad for the purpose, you keep the revs down a bit... Unless you have a tiny propeller...
skunkbait (author)  killerjackalope8 years ago
Hmmm, I do have a 185 Honda engine from an od trike. Starts everytime and runs well.
That'd have some more grunt to it and may well be more reliable, plus you could keep the gearbox, so if you felt the need you could get more speed... The other big plus would be having a self contained motor...
skunkbait (author)  killerjackalope8 years ago
I actually have a Jetski I could sacrifice if I decide to get serious! I thought about grafting it into the rear of a canoe.
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