Lower unit compatibility

[mmike]

I have a 1996 Evinrude 115 which will be used on a barge. In looking at lower units for this motor, I see several choices, limiting them to 20" shafts, it leaves 3 listed as being used on this motor.
There is a small gear case (2.00:1), and two large gearcases (V4 2.25:1 and V6 1.86:1). For my purpose, the large gearcase, 2.25:1 seems like it would be the best fit. Most of my use is low speed, heavy load, so big propeller and high gear ratio would be best. I have a vast assortment of different props and a tach to monitor RPMs.

Here's my question, do all the large gearcases just bolt on, or am I limited to what my motor came with?

 

[HighTrim]

Re: Lower unit compatibility

Check out the FAQS

 

[mmike]

Re: Lower unit compatibility

Check out the FAQS

I'm sorry if this is a stupid and boring question, but I have looked for an answer for hours. Many sites are very clear in telling me what I have on my motor now, the size, shape, color, dimensions, propellers, virtually everything, but I can't find the interchange answer.
The FAQ is very difficult to navigate, at best giving me tons of unrelated posts, the link in your signature lead me to the same answers I have. Local dealers have no idea. I found parts blow ups and compared part numbers, and it looks like exaust gasket and water pump cover are the same part numbers and the different units would bolt on, but that's just a guess.
I have encountered lower unit changes before that were so close, but one small difference and it wouldn't go together.
Not being an outboard mechanic, much of this information is like trying to read a foreign language.

If you could give me a hint to a good search term that would get me to the answer, it would be appreciated.

 

[Faztbullet]

Re: Lower unit compatibility

Is your motor a 90? or 60?? A "big unit" off a 120/140 looper will have the ratio your looking for but you may have to change the driveshaft to make it fit....

 

[mmike]

Re: Lower unit compatibility

Is your motor a 90? or 60?? A "big unit" off a 120/140 looper will have the ratio your looking for but you may have to change the driveshaft to make it fit....

It's a 60 degree motor.
You think the large gearcase will just bolt on even though it has a small gearcase?

 

[Faztbullet]

Re: Lower unit compatibility

Yes it will bolt up but the 120/140 loopers have different length driveshafts due to crank lenght, If you can find a unit off a 1992 or newer 120/130/140 you can swap the shaft with out tearing down the units and use your existing shaft and shift rod without having to purchase another...

 

[mmike]

Re: Lower unit compatibility

Yes it will bolt up but the 120/140 loopers have different length driveshafts due to crank lenght, If you can find a unit off a 1992 or newer 120/130/140 you can swap the shaft with out tearing down the units and use your existing shaft and shift rod without having to purchase another...

Thank you so much.
If I understand correctly, the lower units from 1979 to 1992 120/130/140 will also fit, but they have one piece driveshafts so the length could become an issue? And the one piece drive shaft can be used in a lower unit with a two piece drive shaft by disassembling the gearcase and swapping the driveshaft?

 

[Faztbullet]

Re: Lower unit compatibility

If I understand correctly, the lower units from 1979 to 1992 120/130/140 will also fit, but they have one piece driveshafts so the length could become an issue? And the one piece drive shaft can be used in a lower unit with a two piece drive shaft by disassembling the gearcase and swapping the driveshaft?

That is correct,but watch the shafts length as the older ones was shorter!!!

 

[mmike]

Re: Lower unit compatibility

That is correct,but watch the shafts length as the older ones was shorter!!!

Thanks again.

If I'll be careful with the drive-shaft length because my drive-shaft stretcher is broken.

I vaguely recall hearing about a problem with some of these lower units where they put on a smaller pinion gear to make up for the propeller size difference, and that required tapering the drive-shaft to a smaller size to fit, which created a weak link which became problematic. Will that affect my choices?
Putting a smaller pinion gear is what I'm doing to get the low end power,so it makes me think this 2.25 gear case is the one that was a problem?
Or maybe it's a non-issue because I'm putting a 140 gearcase on a 115, and the lower power demands a less strong gear-set?
As always, input is appreciated.