[MikkiJayne]

Found the smoking gun - a broken valve spring!



The spring broke and released the tension on the collets, which promptly fell out. The next engine cycle pushed the valve down in to the cylinder where it was hit by the piston, and with no tension on it the hydraulic element dropped out of the rocker arm. The valve then got smashed up by the piston, and at the same time the element got smashed up by the rocker. Once the valve stem was sufficiently bent, it got jammed in the guide and the top broke off at the collet grooves. That bit stayed in the guide and the rest got ejected back up the inlet port.

The collets are the only bit left of the assembly that are intact, as they had escaped by the time all the destruction happened. One of them was sitting by #7.

More carnage pics:








The chain guides needed doing. Looks like 100K is the norm for these.