As far as I understand from Stevie a helicoil came out with the bolt and the Cylinder head must have had a crack in it (overtightened by another owner) that had split, and a chunk of aluminium had broken off wrecking the head.
Luckily he noticed a cylinder head bolt was loose when he was cleaning the bike and didn't start the engine as he said the chunk of alloy was next to the cam chain and would have been ripped down into the inside of the engine.
So I think the only way to go is a new cylinder head.
I nipped round Stevies tonight and took a couple of pics...
This is the bit that broke off, it was 2 bits but been bonded together....
It or they came from here...
a different angle...
Not sure if it can be built up, but we did notice that one of the other threads on the head was almost non existent too. It was possible to move the bolt up and down a couple of mm when it was screwed into it and quite a bit of sideways play in the bolt.
It's funny that it is the two rear threads that have problems but the front two are sound.
sounds like this could have gone down on its side at some point in it's life, possibly crash bar helped the front of the cover, but the rear of the valve cover still impacted and damaged the mounts -
