Earl - It's pretty easy to take it apart. Loosen the big bolts on the chain adjuster and remove the starter link to remove the chain. The u-joint should have two set-screws to remove. Note, there should also be a cotter pin through the end of the shaft, inside the u-joint, but it looks like yours is missing & the u-joint/drive shaft is sliding off the shaft. And, your photo shows the coiled pin holding the sprocket to the shaft. Use a pin punch to drive that pin out. If the pin is sheared, it may not be aligned with the hole through the shaft. Getting it aligned to drive the pin through is probably the hardest part of the process. If you can push a wire through, it's lined up and ready to drive out. If not, you may need to pull one end of the coil pin out to find the drive shaft hole, then punch it through.
I sheared the coiled pin on mine twice this winter, and it took about a half hour to replace it. Had to disassemble, as noted above, to freely access the pin, shaft, etc, but if I can do it, anyone can.
As you can see in Charlie's (Digger's) post above, he has whatever you may need.
