Crazy idea... lawn mower motor in a Johnny OB?

[UGLandrum]

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[1946Zephyr]

Re: Crazy idea... lawn mower motor in a Johnny OB?

oh my

 

[BigB9000]

Re: Crazy idea... lawn mower motor in a Johnny OB?

ehhhhhh......... a lot of issues here.

that engine was probably never meant to be used near, in, or around water.
and probably wasn't designed to push a boat along at 4500 PRM for an extended amount of time.

I think, it'll work for a little while, until it overheats. ..or the flywheel/coil(s) rust.

 

[UGLandrum]

Re: Crazy idea... lawn mower motor in a Johnny OB?

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[kenmyfam]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Very adventurous. Not something I would recommend. Too many issues
to list !!

 

[Vic.S]

Re: Crazy idea... lawn mower motor in a Johnny OB?

An interesting idea for a project

The gearcase is held by 6 bolts, I think one is hidden by the trim tab!

The shift rod disconnects at the top. Hidden under the carbs I guess.

Presumably the mower engine is air cooled
So you'll need to make provision for the air supply to and from the mower engine when fitted in the outboard

How will you deal with the exhaust. Presumably at present exhausts to a dry silencer ... you'll retain that and remove the old water pump?

I hope the mower engine revs are in the right sort of range to drive the outboard gearbox.

We will expect to see pictures of it "up and running" when you have completed the conversion.

 

[R.Johnson]

Re: Crazy idea... lawn mower motor in a Johnny OB?

I would suggest a pak of steel wool, and a set of knitting needle's for those part's you can't find.

 

[Chris1956]

Re: Crazy idea... lawn mower motor in a Johnny OB?

You will need to fabricate some kind of driveshaft spline (female) to mate with the male splined driveshaft. You will need to rig up the shift shaft to move up/down manually to shift from FWD to neutral and reverse. As mentioned, don't forget to rig up some exhaust pipe. You will need to get a prop with a lot less pitch, since you are dropping the HP so much.

I would think it would be less work to fix up the original motor, and you would have a better product.

 

[G DANE]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Indeed an interesting idea, only it would be a lot easier, cheaper ( i bet ) and way better to repair the powerhead that is already fittet to the mid-section. I exa. the 20 - 25 HP power head is in displacement similar to a 6 HP lawn mover, motor, putting out 6 BHP at 3000 rmp. Could sound like an easy fit to get a dumped lawnmower and put it on, but count the hours to your first trip !!!

 

[Silvertip]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Mower engines are usually governed at 3600 RPM. So right from the git-go you are about 2400 RPM short of what the original power head provided. They are noisy. That and of course the lost 76 horespower. And restricting the exhaust by sticking it in the water will cut power as well. If you have lots of time, like to waste money on projects that provide satisfaction in that you can say "I've done that" but it wasn't practical, then by all means go for it. But my vote is to fix the engine to make it reliable. My view is that if you consider adding oil to a tank of gas "pesky", they the labor of doing this project becomes a big "huh-what"!!!!!!!!!

 

[GatorMike]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Interesting concept because just the other day I was thinking about putting my 115 Johnson powerhead on my lawnmower. Think about it, I would never have to worry about it bogging down in high grass again. I too ran into some snags though, like I would have to buy about 200 ft of garden hose to hook up the muffs and there is nowhere to mount rod holders on that silly lawnmower.

 

[1946Zephyr]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Not to mention that mower wouldn't have enough room left for a beer cooler.

I would like to see about puting one of those 300hp V8 powerheads in a small street rod. Now there's a cool project.

 

[wilde1j]

Re: Crazy idea... lawn mower motor in a Johnny OB?

I would consider getting a set of oars ...

 

[Chris1956]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Instead of a 115HP Lawnmower, how about building a short shaft jet outboard with a bedpan, an old prop and a heliarc welder, plus a driveshaft.

 

[mitchell6]

Re: Crazy idea... lawn mower motor in a Johnny OB?

So that's what I can do with the old 135 Johnson head I got under my porch but it on the riding lawnmower. It's got 1 burned up piston but still should shoot the mower aross the they yard.
GatorMike figured out the garden hose issue hook up a water trailer behind the mower with some kind of pump to the old outboard that way you don't have to have a garden hose that you will run over sooner or later

 

[wbeaton]

Re: Crazy idea... lawn mower motor in a Johnny OB?

UGLandrum,

Lots of folks have rigged up lawnmower engines to outboard lower units. However, they usually choose much smaller motors to work with. The big 85 hp lower will eat up a lot of power. If you want to build an outboard from a lawn mower motor by all means go ahead. I toy with the idea somedays, too. The problem as I see it isn't that it won't work with what you have, but rather you are trying to cobble something from inappropriately sized parts. Look for a smaller lower unit or a much larger powerhead. I'd suggest picking up an 18-20-25 OMC midsection and lower unit to mate to your 12 hp. A good used +/- 85 hp motor is not expensive or hard to find.

 

[cajuncook1]

Re: Crazy idea... lawn mower motor in a Johnny OB?

Just a thought:

Partout your your current outboard--ebay or craigslist.
-sure you could get decent amount for your lower unit, powerhead, etc...

Since you are willing to settle for 12hp Briggs and Stratton and not concerned with power or speed:

- Use the money you get from parting out your current motor and the money you would have use to fabricate pieces and parts for your project and buy a good used and good running 15hp, 18hp, 25hp outboard.

Hope things workout for ya!

cajuncook1

 

[bob johnson]

Re: Crazy idea... lawn mower motor in a Johnny OB?

run, the men in the white jackets are coming!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

yeah...I think a hairball lawnmower-outboard LU conglomeration that was never ment to meet, all fashioned from garage tooling, and prayers...and maybe some silly putty.... would be way way way less of a head ache than a finiky 1970 something 85 hp Johnson!!!!!

YEAH

I mean i think. Yeah.

bob

 

[1946Zephyr]

Re: Crazy idea... lawn mower motor in a Johnny OB?

run, the men in the white jackets are coming!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

yeah...I think a hairball lawnmower-outboard LU conglomeration that was never ment to meet, all fashioned from garage tooling, and prayers...and maybe some silly putty.... would be way way way less of a head ache than a finiky 1970 something 85 hp Johnson!!!!!

YEAH

I mean i think. Yeah.

bob

Hey, anyone ever watched "Junkyard Wars?"

 

[McGR]

Re: Crazy idea... lawn mower motor in a Johnny OB?

So basically you want to trade one of the better outboard motor designs ever,that was capable of pushing a typical rig between 30 to 40mph for a crazy rig that may push your boat 2mph with the wind at your back?...

Why not fix the 85hp instead? They were quite good motors. I have a 34 year old 1976 85hp (exact same as yours) that still runs great. In fact, I am going to sell it this spring and I'm afraid that I may be trading up to something worse.

Parts are generally available for that motor and they are fairly easy to work on. I think it would take considerably more effort to do what you are suggesting.