Well, the problem child continues to present me with problems. The idea of just “taking a bit off the face” of the sprocket carrier to move the stock ID sprocket toward the centerline turned out to be unworkable; the wall thickness of the carrier casting just isn’t thick enough to do that. So, I came up with an alternative. The diameter of the carrier behind the sprocket location was ≅105 mm. I went looking for a sprocket with an ID just very slightly less than this. I found it in a sprocket for late ’90s and early ’00s Ducatis. (Unlike the OE sprocket from the GS450T, which was 530, this would match my Bultaco’s 520 countershaft sprocket.)
A little lathe work would give me the ability to mount the Ducati sprocket behind and flush with the stock sprocket location. I could then cut down the stock sprocket, turning it into a secondary sprocket carrier. I drew up a profile of the carrier casting in section at its thinnest point, to ensure that I wouldn’t end up removing too much material. As it turned out, I wouldn’t be removing material from any of the thinnest portions of the casting.
That would allow me to mount the sprocket, but how to bolt it in place? That’s where the OE Suzuki sprocket came into play. I could cut the perimeter off and turn just the center and spokes into an outboard “spider” that would locate the Duc sprocket securely, and give me something it could bolt to from behind.
Unlike the aftermarket JT GS300 sprocket I had been intending to use, the stock GS450T is really thick, with wide spokes, and made of unbelievably tough steel. Cutting it down with my recip saw and turning the spokes on my lathe were challenging, but eventually I had it shaped.
Compared to the sprocket, turning the alloy Suzuki carrier was a piece of cake.
Even though I still need to drill the outer holes in the spokes of the old sprocket for the Duc sprocket to bolt to, I had to assemble it all on the bike and check my handiwork. The chain run lines up perfectly, and even though this arrangement looks a bit odd, this setup will be strong and safe.
