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Old 10-09-2018, 10:23 PM
Zm040311 Zm040311 is offline
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Default lawn mower with outboard engine

So i just got a 1974 mercury 4 cylinder outboard engine for free with 85 hp and i have a old lawnmower frame and transmission and im asking for ideas about how i can go about this project
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Old 10-09-2018, 11:45 PM
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Well you'll have to come up with a way to cool the engine, as these pull water from the lake to cool it down. This is why people who winterize their boats use a pair of water muffs and hook it up to a garden hose. Otherwise you'll overheat the engine.
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Old 10-10-2018, 12:32 AM
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Quote:
Originally Posted by Zm040311 View Post
So i just got a 1974 mercury 4 cylinder outboard engine for free with 85 hp and i have a old lawnmower frame and transmission and im asking for ideas about how i can go about this project
Are you making a boat out of a lawnmower chassis? That engine needs water going through it

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Old 10-10-2018, 05:30 AM
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I'm guessing it has a wet exhaust... That will complicate things significantly.

If you can figure that bit out, you'll need a very large radiator, as boat engines are really designed with cold (comparatively speaking) water in mind. Where a car engine likes its ~180 recirculated water, boat motors are designed for a much lower supply temp.

Plus... The mower transaxle will never handle that kind of power. Something's going to snap. Most riding mower transaxle can't even handle the full power of the stock engine. The engines are sized to spin the mower deck, not just move the mower.
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Old 10-10-2018, 07:25 AM
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while it makes sense to design an engine for lower water temps (otherwise the temp difference can cause stress cracks)
I don't see how the engine couldn't be cooled with recirculating water from a nice big radiator setup.

I mean all that's needed is to stop the engine from overheating (say keep the recirculating water from boiling) I doubt it raised the incoming water temp by more than 20C when it finally,
leaves the engine again.
So a supply temp of 70-80C should be good IMHO...

It's unlikely the engine has a narrower passageways for the water, since you need a certain amount of thermal mass to cool the engine and it's easier to move more water at a slower rate than less water at a higher rate (pressure and such)

And by that tiny little impeller I see in the waterpump here
And how it's set up I'd say it's a fast spinner and producing near to neglible pressures..
frankly I have a hard time imagining how that thing could suck up water if the engine ever ran dry...

But true.. you have to make sure the cooling is sufficient if you don't want this to end quicker than it started.

What makes it very uncomfortable to use in a kart is that these engine are designed as vertical engines.
and converting that to a horizontal shaft might be a task of it's own..
just the mounting tabs alone will likely haunt your nightmares for a while.

'sid
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Old 10-10-2018, 07:32 AM
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Sid, I'm guessing he wants to use it in that mower in a vertical shaft configuration, simply swapped out for the stock vertical shaft engine. At least that's the impression I get. It's why I mentioned the strength of the driveline being a problem
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Old 10-10-2018, 08:02 AM
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Oh right!

but still mounting will be non trivial at least.. since I doubt the mounting plate for a -let's just say- 10horse single cylinder is up to par for a 85 horse four cylinder engine's weight and inertia.

And IIRC larger boat motors typically HANG
(mounting spot is on the upper most cylinder)
while lawm mowers typically have the engine bolted to the deck.

So at least there would be some serious bracing to do IMHO.

And you're perfectly right.. IF that's an intended "simple swap" then all of the driveline will be shredded to pieces within the first few seconds.
if PO's lucky enough the belt goes first otherwise there'll be metal shreds flying all over the "now no longer to be mowed" lawn

'sid
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