It is missing too much material between the valves and around the seat. It could be welded, but again, heads aren't rare enough yet to justify the cost. What model head is that?

Its an E31

Look like corrosion or detonation?

Not too many 31's around that don't have corrosion issues and too far gone for repair. If that's the only issue it might be worth saving. Weld repair to go along with new seats and you have a good little performer. Put the bigger valves(L28) all the way around and a hot cam on a L28 block and zoom- zoom.

I wish I had an old head like that just to play with.

I believe its detonation, the rest of the head looks almost brand new, I don't understand why just one cylinder would be like this.

Anyone know what temp is safe to take the head up to?

That looks like electrolysis......Never use tap water or well water in your radiator...use distilled water and anti freeze. The metals and other contaminants in H2O cause an electrical reaction that eventually eats a little tunnel under the head gasket and gets in the cylinder. It reacts with aluminum and other metals and eats it away. This usually happens when the car is sitting for a long time. I'll bet SteveJ can help with this.

Just realized that my other post was incorrect. The FSM describes reaming the head to to the proper size to fit the seat. And the interference fit spec. is at the end of the chapter in the specs. section. Recommended temperature for inserting the seats is in the chapter also.

Too many numbers to piece-meal them out. Good luck.

Index of /FSM/240z

So you think there was a water leak in this cylinder?

Not necessarily......the electrolysis eats a little tunnel under the gasket, into the combustion chamber. The water continues to eat aluminum and other metal. I had one do the same thing. Can't remember whether it was 5 or 6. It's like an electric current flows through the water and slowly eats metal like a weak acid. Probably has something to do with the electrical system being neg ground and a very small short in the circuit somewhere. Like I said SteveJ is our resident electrical guru and could probably explain it. The head can be welded, ground down and new seats installed. You need a pro though....don't want to warp the head.

Good Luck

Guy

What cylinder number is it?

If the rest of the cylinder head is as good as you say, then the problem is obviously isolated to that cylinder. I would definitely consider keeping and fixing it.

where do I find that number? On the end of the head firewall side,

there a number sign and under it is says 1, is that it?

My number 6 cylinder (the one closest to the firewall) on my E31 head was eroded to the point where the exhaust seat was nearly falling out. The shop I went to welded it up and ground it flat while doing the other work.