12.9 hp Chrysler 280 outboard

loose rivet

Petty Officer 2nd Class
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Jul 31, 2011
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151
I happened across a 12.9 hp long shaft Chrysler today, got it for so cheap I had to take it.
Its not run in ages but its complete and fairly clean.
Now the question is that I don't have a sailboat and have no use for a long shaft motor but was wondering if there is anyway to crossbreed this thing with a short shaft 10hp or are they totally different motors?
I've got a later model Chrysler 10hp that has low compression, are these an offshoot of the 10hp engine family or are they their own stand alone model?
I like the large prop on the 280 model, and the lower gear ratio. It appears to be a 3 to 1 ratio lower unit.
I'm tempted to just make an adapter bracket up and get this running and give it a try but I feel I'd save some weight if I can make it shorter somehow. The lower units are different and obviously won't interchange due to size so the question is will the short shaft lower end of a 10hp work in place of the 280's original lower unit? (Is the driveshaft size and spline the same in the power head? Will the total lower swap over or will the 12.9hp power head fit onto a 10hp mid and lower?
 

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
Re: 12.9 hp Chrysler 280 outboard

Gotta figure out the year and serial#s on both motors.
Then I can compare the parts.
The longer units usually had the drive shaft that only fit the longer motors.
You might find a shorter lower?
Build a taller bracket?
 

Frank Acampora

Supreme Mariner
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Jan 19, 2007
Messages
12,004
Re: 12.9 hp Chrysler 280 outboard

Depending upon the year of the 10 and the 280, the loer units should simply swap. Early long shaft engines had a 5 inch extension and extra water tube. The sailor model has a complete leg. Removing it should allow you to attach the 10 HP leg. I am reasonably certain that the drive shaft diameter and splines are the same as is the upper shift rod.
 

loose rivet

Petty Officer 2nd Class
Joined
Jul 31, 2011
Messages
151
Re: 12.9 hp Chrysler 280 outboard

The 10hp leg went right on. The motor turns out to be a 1979 12hp not a 12.9hp, so its newer than I thought.
I was half hoping there would be some way to make use of the larger prop on a short shaft configuration but for now its got the 10hp lower on it. I may work on getting the 280 lower in shape and give it a try on a bracket to see what it will do. I like the larger, low pitch prop idea for lower speed handling or trolling.
 

Frank Acampora

Supreme Mariner
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Jan 19, 2007
Messages
12,004
Re: 12.9 hp Chrysler 280 outboard

The gearcase, gears, propshaft, and ten inch propeller from the sailor model are actually from the 20-35 HP engines. That is how the sailor uses lower ratio gears and develops much more thrust for driving displacement hulls. In fact, if you look further back, you will see that the earlier 20-35 HP models used to have a smaller 9 inch prop and were changed by the factory to the 10 inch props to improve their power delivery to the water.

Because of the size difference of the gears you can not simply swap them into the smaller 8-15 HP gearcases. AND, similarly, there is no good lower unit casing that will accept the gears and bolt to the 12 HP midleg.
 
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