Convert Small Sears outboard

[mark_gober]

Hey everyone,

I've question that needs some answers/advice. I recently rescued a very small single cylinder outboard from the curb. It's a Sears engine and is very old. I'd give you a model/hp number, but that information was long since gone. The motor is siezed up and the gas tank has a hole rusted in it. (I didn't realize this until I unloaded my new toy at home.)

Now I realize that most people might just throw this motor away, but I'm thinking I might be able to revive/frankenstien this into something useful. Upon closer inspection of the powerhead, it looks VERY similar to a standard lawnmower engine. The bolt pattern on the bottom looks a few inches narrower than a traditional lawnmower engine. I happen to have a brand spanking new 6.5hp honda lawnmower engine that I procured at the local Northern Tool for a whopping $25. (I caught those suckers looking) Anyway, I'm thinking I might be able to modify this motor to place my Honda engine on it. In order to achieve this, I think I'd need to construct an adapter plate in between the powerhead and the lower unit to convert the bolt pattern. My only question, and I haven't explored it yet, is how that older powerhead connects to the shaft that leads down to the prop. If it is somehow coupled to the shaft of the powerhead, I'm probably in luck. I can't imagine that it has a long shaft all the way from the power head to the lower unit that is one solid piece.

I have, in recent years, seen those small boat motors that have these lawnmower engines on top instead a more traditional powerhead. Any home built types out there that might be willing to offer suggestions. Normally I wouldn't pursue such an endeavor, but the outboard was free and the replacement motor was $25. This has the makings of an extremely cheap backup motor for my humble 14' aluminum fishing boat.

 

[CATransplant]

Re: Convert Small Sears outboard

It's been done...many times. The key is the coupler between the engine's crankshaft and the driveshaft of the outboard. Until you pull the engine off your outboard, you won't have any idea of how to hook things up.

Generally, outboard driveshafts have a splined upper end that fits into a splined recess in the crankshaft. That won't work, of course, since it would be an expensive proposition, indeed to create the recess.

One guy here did this. He made an adapter plate to mount the mower engine and a coupler that fit both the crankshaft and the driveshaft. I don't remember how he fastened the driveshaft into the coupler. Setscrews won't cut it.

When you're all done with your project, you'll have something that works, but it will vibrate like all getout and will end up being less satisfactory than you think.

Still, it might be a fun project for you.