"I used nylon lock nuts on my rag joint, so I don't understand why it came out of alignment. I replaced the rag and the mounting bolts, and got a new chain and it reduced the wobble. "
My kit came with the small nylon locknuts, I used them and reused them which apparently you're not supposed to do with nylon locknuts
. When you use a locknut and take it off, the nylon can get damaged especially if you put a considerable amount of force tightening it down. I know ive done this and scratched my head about it, and it makes more sense why other people would have this problem.
Also i stack them: bolt-washer-sprocket-rag-(spoke)-rag-metal plate-lockwasher- standard nut now.
I have a 34 kings sprocket and it lined up perfectly on both wheels there is not a lot of space for it to move as in the other ebay or kit sprockets i have the center hole is smaller.
I think the rag joint is a bit flexible but if your tolerances are pretty tight everywhere else you wont see things shifting around much.
If the rag joint scares you, shell out some money and buy a hub adapter and or use a smaller gear and lower your torque. but for reference Im running a 4.5 hp arrow motor all the way out to 35-40 mph sustained, all the added torque hasnt moved my rag joint or snapped my spokes and ive been riding cross town for months dumping the clutch and everything.
In my case, my preference is to trust the rag joint until i see evidence that it can't handle the torque. In others cases, they don't want to worry, they buy the upgrade. For some people, their life may depend on buying a sprocket adapter, but for me, I'm smiling and riding on some cheap rubber.