Compatibility questions: Force 90 and Force 150 circa 1993

[HotTommy]

I have a good running Force by Mercury 90 HP outboard circa 1993. It has a 20" shaft lower unit. I have the opportunity to buy a 150 HP Force of the same year with a 30" shaft lower unit. The 30" motor is too long for my application. I'm wondering if I can swap the lower units without too much trouble. I'd like to end up with a 150 HP 20" motor and a spare. Does anyone have a definitive answer?

 

[GA_Boater]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

I don't have an answer, but it might be easier to swap power heads and covers. Look up parts diagrams for both motors and see if the power head to midsection gaskets are the same. At the same time you can check the lower units for part number compatibility.

 

[HotTommy]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

Thanks for the reply. ... It makes me realize I may not have used the right terminology, so let me rephrase the question. Is it possible to combine the parts of these two engines so I end up with the 150 HP upper part from one and the 20" shaft lower part from the other? ... I realize that someone more knowledgeable than me could probably figure this out from the parts numbers, but I don't trust myself to do it without spending a lot more time learning about such things.

 

[HotTommy]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

I found this thread about a 120 to 150 swap: click here
I understand it to say the answer is, it depends. If I misunderstand, please correct me. Otherwise, I think I know enough to pass on the opportunity to purchase the 150. There are too many unknowns for this swap to be a sure thing.

 

[Frank Acampora]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

Yes, you can make a long shaft 20 inch 150, but is it really worth the time and effort? You need to remove both power heads and put the 150 onto the 90 midleg. Removing the 150 powerhead is way more complicated than removing the 90 simply because of room and weight--it probably weighs twice the 90.

If you have the time, skill, inclination, and a good hoist, then by all means go for it. But unless you have done this sort of thing before, it will be a winter project.

It is not a 30 inch leg, it is a 25 inch leg and your time would be better served raising the transom 5 inches.

 

[HotTommy]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

Thanks Frank. The seller claimed it was a 30" leg, but if there is no such thing, he was probably measuring it wrong. I might be able to make a 25" leg work without all the swapping.

 

[jerryjerry05]

Re: Compatibility questions: Force 90 and Force 150 circa 1993

To make the lower 30(25) a 20 all you have to do is change the driveshaft.
You'll have to modify the bottom cowl to make it work.
Then a lot more fitting and adapting.
The linkage maybe? The wiring?
Depending on the serial#s it could be easy?maybe not.
Actually a big job but you've got all winter.