I was out for a thrash yesterday on the 660 Ten. Was really going at it (about 80mph) passing vehicles, when the chain came off, not broken, just off.

Got it back on without too much aggro and headed more sedately home.

Up on the table this morning to get a better look and the damage appears minimal, scrapes on the outside of the Swing Arm but no big gouges.
Rear half of the Upper Chain guard has gone as has the lower Chain Guide to the rear sprocket .This Lower Guide was as our own Stoic Boy had recommended some while back. The only difference was that I'd split mine in two for easier fitting, as several have done on here. I'm starting to think this is not a good idea. The right angle mounting plate had been cleanly broken along the bend in the metal (3mm alum). The two mounting bolts/nuts were undamaged and still in position.

Bike is 2011, bought new 2013, 4750miles. The chain is not stretched and has still a fair bit of life left. Scottoiler from new. There is no apparent wear on the rear sprocket however there is more wear on the front sprocket than I would have expected at the mileage.

The chain may have been slightly loose but not excessively so, I'm pretty careful. I'm drawn towards the mounting plate of the Chain Guide suffering a vibration fracture but would like to hear what the collective think.

I'm fortunate I know....Could have been so much worse.