Question about the 1990s era 75/80 and 90 lower unit swap to 100/115 and 125hp

[dog22]

Don't know if a 1993 Mercury 75 hp lower unit will work on a 1991 Mercury 115. According to my manual, the gear ratio for the 75 is 2.3:1, and the gear ratio for the 115 is 2.07:1. Please let me know if someone has tried this and had good results

 

[Texasmark]

Don't know about that model era but it may be/probably is related to the 2000+ year models. I had a 2002 90 3 cyl. and a 2002 115 4 cyl. and they seemed to be the same except for the extra cylinder extension making the cowling taller. The OEM service manual showed reference to the 75 (Jet) all the way through the 125. I didn't have a parts list so I can't be 100% sure but other than the changes that supported the 4th cylinder addition, why would the rest of the engine be different?

 

[Chris1956]

If you look on the crowleymarine web site at the part numbers for the two gearcase shells, you may get an idea of what will interchange.

Of course the part number of the gearcases themselves will differ if they have different gear ratios. Sterndrive Engineering (SEI) may also give some clues.

 

[dog22]

If you look on the crowleymarine web site at the part numbers for the two gearcase shells, you may get an idea of what will interchange.

Of course the part number of the gearcases themselves will differ if they have different gear ratios. Sterndrive Engineering (SEI) may also give some clues.

I already have the manual that covers both engines, but since the 75hp powerhead blew up, I have a 115hp powerhead sitting around that I want to mount in the 75hp lower. The power tilt and trim are the same

 

[Chris1956]

Gee, that is a different question.

 

[Texasmark]

If you look on the crowleymarine web site at the part numbers for the two gearcase shells, you may get an idea of what will interchange.

Of course the part number of the gearcases themselves will differ if they have different gear ratios. Sterndrive Engineering (SEI) may also give some clues.

That's true....the 90 had a 2.33 and the 115 2.0 lower unit gear ratio.