Check this out

[400hondaex]

This is out of my 300ex. Don't know what really happened but it looked like the 2 bolts on the sproket backed out and you can guess the rest.
http://img161.exs.cx/img161/2662/645.jpg

[chad502ex]

ouch!

[400hondaex]

yea I had it fixed then sold it 5 months later