'91 120HP Lower Unit

[Capt. Steelhead]

Hello fellow wrench pullers, I need to change my '91 120 HP l/u out, I have a 125 Hp U.S Marine I believe a '89 everything is the same except 120 is two piece driveshaft however there are slight differences on the height of the two waterpump outlets the older style waterpump is about 1/2" shorter than the '91 which has the newer style larger Plastic/ stainless steel impeller liner. Question if I buy the new waterpump kit FK-1069 (older style) will it come with a longer plastic bushing than the one thats on the '91? it must be different because the '89 waterpump outlet hole has a smaller I.D than the '91. Anybody have a experience with these slight differences. Thanks, Paul

 

[Frank Acampora]

Re: '91 120HP Lower Unit

Damn! Water pump kit does not come with a parts description. However, if the plastic seal is not included, it is only another 4-5 bucks.

And yes, that is the only important difference. As long as the shaft length is the same, the lower units are swappable.

One caveat though: The 89 is a 1.76 gear ratio and the 91 is a 1.92 ratio. You may need to change the prop by dropping 2 pitches to keep RPM up at the correct range.

 

[Capt. Steelhead]

Re: '91 120HP Lower Unit

Thank you for the help Frank I was hoping you were out there on this one. What about a '97 Force 120 HP would that work better I see one nearby that I could acquire and if I didn't have to get a new propeller I might be ahead plus it's newer but better? don't know that one. In regards to FK-1069 waterpump kit I'll hold off till I get a answer I'll look in the search feature. Thanks again Paul

 

[Frank Acampora]

Re: '91 120HP Lower Unit

97 is a Mercury design lower unit and will not bolt to your midleg.