Re: Research on finding a ss prop for my 120hp force but no luck please help
I don't have and have not yet worked on a very late model Force 120. However, I do have a couple of late model 40, 50, and 70 HP engines. These engines use a Mercury lower unit similar to Merc 40 and the props--10 inch diameter--from the Merc 40 will fit all of them.
During the years leading up to the demise of the Force brand Mercury started making changes to lower units. Two of the most significant was the incorporation of a Merc style water pump with Merc method of keying the impeller to the shaft and a stainless "cup" inside a plastic housing and gearpaks and shimming similar to Merc.
Therefore, it is not unreasonable to assume (ohhh! there's that word again) that the 1998 Force 120 uses a Merc lower unit also. Indeed, the late model Force engines use the same lower unit mounting bolt pattern as Mercury branded engines. Mercury might have used the lower unit from their 90 which is the smaller gearcase. Based on other Force engines, I doubt they used the larger diameter gearcase lower unit. BUT--- The only way to know for sure is either measure the gearcase inside diameter at the prop or have someone on the forum that knows for sure to chime in.
To clarify, Mercury uses two sizes of gearcase diameter: a 4 inch diameter and a 4 1/4 inch diameter which fits larger, more robust gears. Both use the same size 15 spline prop shaft. However, external hub for the larger prop will not slide inside the lip of the smaller gearcase and the smaller diameter prop will leak too much exhaust gases if installed on the large gearcase. So, in either case, all Mercury 15 spline props will not fit the Force lower unit.
Again, as I said before though, you must be willing to think outside the box. Many props are listed for other engines (some foreign for example, but I have not yet tried a Honda prop) yet, in removable hub props the base prop without hub has the same part number while a different removable hub is used for different engines.
If indeed Furyman has a 4 inch lower unit, then this is the same as earlier Force engines and a through hub exhaust prop from 1990 (dual exhaust) -1998 Force engines will work as will props listed for the smaller gearcase merc 90 HP engines.
