’60s lark / seahorse swap

[putback]

I have a 1961 lark 3 40 hp cable shift and a ’62 super sea horse 40 hp electromatic. The lark being pre 1962 has the potential crankshaft problem. The Seahorse gear case is locked up and has the potential elect shift problems. Both have good compression neither have been stripped down yet. Question is how difficult or even possible is it to use the Sea horse powerhead on the Lark 3. It probably seems more effort than its worth but I have a hull about ready for power and the lark 3 is the perfect match. 12 months and this is all I can find in my area.

[chris-p]

Boy, where are you from. These motors are everywhere in my area!

Potential is the key word here. Me personally if I were you, I would run the Evinrude, and not worry about the crankshaft. Yes they were weaker, but how many have you actually seen break? Don’t know, how about you guys that serviced these in the 60s/70s, was this an actual problem?

[kerry]

In the late 70’s I had a 1961 Johnson 40 break the crank. Two hour tow upriver to the ramp. No warning. I still see the Bigtwins of the suspect years for sale, so maybe its the luck of the draw, but not with my $$$. (or, not without a backup kicker. I was a teen, didn’t plan for bad luck.)

If you have too many, AND not enough, you're a collector.

[garry-in-michigan]

I believe the powerheads are interchangeable, but have never tried it. . . . . ❓

[1946zephyr]

Yes, they are interchangeable. I have done it. Yours is even closer in design, between the two than mine were. But like Chris says. Just run the Lark until it dies, then use the Super Sea Horse powerhead.

I once put a 1968 Lark X powerhead on a 1959 Johnson RDS -21B and it worked awesome!! Five more horse, without any mods, plus I had a 50:1 motor.

I also had a ’61 Lark III and it was a nice unrestored copy. Very reliable motors, in my opinion and will last for years if treated right. One good preventative for keeping the crankshaft from breaking, is make sure that your prop and drive pin are in top knotch condition, because it’s when these motors over rev without a load, is what does most of the breaking. Never over rev these, while in neutral, either, because you could possibly see some metal come unglued right before your eyes.

[frankr]

Having serviced very many of those various year models, I say that any broken cranks that I’ve seen are extremely rare. As for the swap question, I can’t think of any problem offhand. Any differences would be the stuff that hangs on the outside, such as wiring harness, etc.

[Casey Lynn]

Gotta’ go with Frank on this one. The crank issue is a bit blown out of proportion these days. There are still a bunch of those engines out there that never broke a crank and ran reliably. Also, you may have an engine that did break one and had the powerhead replaced already. Regardless, if that is what you have…..run it!
What I do seem to remember here is that the physical size of the crank changed somewhere around 1962? When that changed the driveshaft changed as well. Do some homework on part numbers and you should come up with the answer to that one.
Believe part of this question already was answered on another forum.

[putback]

Thanks, I appreciate the info & insight. Helps to know my options from people with experiance. The more I learn about old outboards the more interested I become, I can see where this is going. Lark started to day. I’ll get to the Seahorse soon. I’m gonna strip the lark down completly, if it checks out ok I’ll reseal it and use it. If it does’t I now know my options. Anybody has any input I’m listening. Zephyr’s post mentioned hiding newer stuff under the old bonnet. I’m an old car builder, loved sleepers, that got my attention.

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