mishar

Right, there is rev limiter in the engine computer too. It should work by cutting firing and fuel immediately when max rev is reached. If that is the case it shouldn't go any higher because there is no power to overcome resistance. But if they played with drive by wire throttle in order to prevent over rev than there is certain inertia that can cause damages. Usually more than one valve.

altaf

Before and after

haggisuk

If I were you I would have scrapped that head and cams, the forces involved to do that damage may well have damaged the followers or cams.

As was mentioned by mishar I would be paying close attention to the intake manifold etc to see if there is parts missing that were ingested by that cylinder.

Actually looking at the photos a bit closer there is deformation on the casting of the other cylinders squish areas, defo been something sucked in through the inlet into the chambers.

There is an S8 that i know of recently that had a top end rebuild due to the very same thing.

dvs_dave

Wow, what a mess. Looks like it dropped a valve into the cylinder?

I hope the repaired head is ok as it still looks a bit of a mess in there.

mishar

This is how head/valves look when timing belt skip a tooth or two. This head is in a much better condition than OP's and it is $245.

MP4.2+6.0

I think we have asked repeatedly about the background of what happened. Not just that the motor stopped, but any underlying background or history. Modifications, maintenance, noises, or any other pertinent details. Why no information about that?

Regardless, I would hesitate to re use that head. I know it has been rebuilt and all, but in addition to the other comments, look carefully at the sealing area of the cylinder where the damage occurred. At about the 1 o'clock position is a relatively large nick/dent that could not be removed with the normal milling/planing that was apparently done. If you compare that picture to the one showing the damage, it looks like the head gasket sealing ring runs right over that area. If it were more inside the cylinder area and clear of the sealing ring area it would be less of a concern, but of course modern engines push the valves way out to the edges of the cylinder wall. Without seeing the disassembly, I can't be sure of the valve seats, but that nick isn't going away, nor the missing chunk of metal in the head between the two exhaust valves.

mishar

I've just noticed that cylinder two also digested something. Much less damage but noticeable.

I would not use that head. As MP said, there is a missing chunk of aluminum that will change compression ratio and deep dent that can compromise sealing. Besides that I would be concerned about valve seats and overall aluminum deformation. There might be now invisible cracks leading into the coolant area.

Pashamad

I would not use that head. As MP said, there is a missing chunk of aluminum that will change compression ratio and deep dent that can compromise sealing. Besides that I would be concerned about valve seats and overall aluminum deformation. There might be now invisible cracks leading into the coolant area.[/QUOTE]

101%! I CAN imagine how piston and cylinder wall looks like!
Unfortunately, we see only one side of the MOON!