This week-end, I had to disassemble an engine from a Kawasaki versys 650 (early). The bike lost power while making ugly metal sounds. It never started again. RIP.
Context: 108.000km, mostly highway usage, maintenance OK, everything right (oil, coolant, tappet clearance...)
It looks like the cause is an exhaust valve that got cut in half, its head falling in the cylinder, obviously destroying everything.
But can this be the source of the failure? Can a valve simply break apart like this? Otherwise, what could have caused this?
The other valves unsurprisingly bent, none of them broke. The spring was all right, nothing noticeable on this side. One of the other valves had lost one "half clip thing that lock it in the spring", I don't know how it is called in english (demi-lune in french) but I think it happened during the breakdown.
Here is an imgur album with close inspection of the cylinder head: http://imgur.com/a/KyAqt
can a valve simply break in half without any reason?