
When we got back I popped the top plug of the chaincase and could see pieces of one of the tensioners, so I figured that was the only problem. I went to replace the tensioner today, and found that the chain had jumped out of place on the bottom sprocket, and had stripped most of the cogs off. The one whole row is gone, and half of the other row is worn off.

I've worked on a bunch of mid-mount JDs, but never seen anything like this. I'm guessing the tensioner shattered first, which loosened the chain just enough to jump and strip the sprocket. There was a piece of the tensioner jammed in the sprocket, so that may have contributed to the chain jumping out of place.