Today I mounted one of the rear sprockets to the BH hub. These sprockets come blank, with a 7/8" center hole. I had to lay out and drill the 4 holes to bolt it to the hub and also bore out the center hole to 2 1/8". I had to use my big ol' honkin' 14" faceplate for this bit of backyard machining. I had to, first, machine a plug to fit the center hole. this was used to find the actual center of the sprocket to lay out the mounting holes and later to attach it, concentrically, on the faceplate Once I centered it up, it went off without a hitch. I ended up with a center hole that was a bit over the 2 1/8 that I was aiming for but no biggee. It'll be fine. There will be a second sprocket next to it since I will be running two chains. I'll wait until I get the front sprockets mounted up before I machine the other one. I have the QD taper bushings coming in from Grainger on Monday. These are different from the ones that BH uses. Additionally, these industrial sprockets are made for #60 chain which is 3/4" pitch. 630 motorcycle chain is also 3/4" pitch, but narrower. I will be running M/C chain, so all 4 sprockets will need to be machined thinner. My old lathe is getting a workout. If you're any kind of gearhead, shop around for an old lathe. They are indispensable. Plus, when people come into your shop, they will know that you kick ass.
I received the QD bushings and after mounting them and the sprockets on the Curtis output shaft, it looks as if the outer, rear sprocket will bolt up to the hub and line up pretty well. The inner cog will need to be bored out to 6" to fit over the hub. Both of them will be separated with a 1" spacer, drilled and bolted together in a three piece sandwich. This should be done by next week as I am over committed and won't be able to work on it much this weekend