I ran the 38 tooth Bikeberry cog today. I had to mill out the center hole to fit on my hub like the original (they were close, but not the same size).
Drilling the holes was a pain. I suggest marking them all with a magic fine point marker, and drilling pilot holes on 7 (2 will overlap the original 5 bolt circle). I used a Vise Grip to hold them for marking. I used a Rat Tail file to elongate the overlapping holes. I used small flat washers on the screws, under the screw heads, to compensate for the oversized/odd holes, and the others to match.
Well, I got it done, and it works well. The 48cc (well broken in) tows along about 3-4 mph faster and takes off just about like it did before. I topped out at 33mph on flat ground, wide open, after moving the C clip one notch richer.
I don't think the 48cc can work with the 36 tooth or 32 tooth, unless you have some power add-ons like a performance pipe and engine mods.
If you can, go with the pre-drilled flat sprockets on the vendor websites like Dax etc It would be way easier, and you can flip the sprocket when it starts wearing, for more life.
