I'm having some problems with this one Deejay. The 14" SB45s had the Briggs 60102 engine, which had a 5/8" output shaft. The 17" SB45s had the Briggs 80102 engine, and I can't find the output shaft size for that one. (The next size of engines up, the 9 series, had 3/4" output shafts.) The Honda GX120 normally has a 3/4" output shaft. There is a version of the GX120 with a 5/8" output shaft, but it is described as "threaded", so I doubt that would be much use.
I've heard there are SB45 clutches available with a 3/4" bore, which suggests to me that the wider models had Briggs engines with a 3/4 inch output shaft.
So Manch, I suggest you check the shaft diameter of your Briggs engine, and tell us what it is please, so we'll know next time. We already know that the 14" SB45 had a 5/8" engine shaft with a clutch to suit that, so conversion to a GX120 required a clutch change on that model. Your SB45 looks like a 17" in the picture. If its 80102 engine also had a 5/8" shaft, your clutch bore will be too small for the GX120. If your 80102 has a 3/4" shaft, the GX120 should fit without any changes being required.
