Force engine 90 vs.120 compatibility

[racer-x]

Hello guys.
I know that the Force models were basically unchanged from 1990 to 1994, and then Mercury started to phase in their parts.

I have a 1990 dual exhaust model, and is a 90 hp.

Are there any experts out there that know the similarities or differences
from a 1992 to 1994 120 hp models?

I have a chance to buy a parts motor, and it's a 120.... Just in case I need a bottom end in the future (or are the gear ratios different? The 90 hp is a 1.93), and I will hopefully be able to use the prop off of it for now.

 

[Frank Acampora]

Re: Force engine 90 vs.120 compatibility

My experience is limited with engines after 1990 but there are some similarities.

If the lower unit of the 120 is indeed still a Force lower, and not a Mercury, AND if the water pump and splines on the drive shaft were not yet changed by Merc, then it should bolt right on. HOWEVER, it may have a higher gear ratio --on the order of 1.78 to 1. This will affect the power output on your 90 and even going to a lower pitched prop to compensate, you will still be a couple of MPH slower at top end.

Carbs are different and can not be interchanged. Pistons MAY be the same at 3.375 diameter and if so can be used. Rods and bearings also are interchangeable.

Trigger assembly is different but the stator may be interchangeable.

And, of course, if the crankshaft and drive shaft splines are the same as the 3 cylinder, then the whole 4 cylinder block can be mounted on the 90 leg