Severe Exhaust Valve Pitting- What Causes This?

[JusMX141]

I'm in the process of rebuilding the engine in my girlfriend's Sunfire. The car has 150k on it, and was starting to burn alot of oil. I removed the valves from the head, and the seat area of every exhaust valve was SEVERELY pitted- some worse than others. The seats in the head aren't really damaged at all, just pitting on the valves themselves. The result was inconsistent compression across the deck....180, 90, 140, 185. The lowest cylinder, #2, had the worst pitting to the valve base.

A close DSMie of mine said that when he pulled the head on his '91 TSi to change the head gasket, he found that his exhaust valves were pitted as well.

My question is what the hell causes this? Bad (cheap) gas? Too much timing? Are there any ways to fix / prevent this so I'm not pulling the heads off all my high-mileage cars expecting valve damage?

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[Splitpi]

High exhaust temp from too little fuel?

 

[Defiant]

Being a GM. A damned, stinking GM.
What year was it? Was it meant for leaded gas? The reason tetraethyl lead was used in gasoline was for valve seat lubrication and protection, supposedly. Had you done a compression test before opening it up?

 

[Supa Dexta]

There was no sunfire on earth that required leaded gas. Possible fuel and/or heat issue. I'd be more apt to blame it on shoddy materials with the gm quality f the time. It's also pitted the same as steel thats left to get wet/hot/wet/hot

 

[JusMX141]

Being a GM. A damned, stinking GM.
What year was it? Was it meant for leaded gas? The reason tetraethyl lead was used in gasoline was for valve seat lubrication and protection, supposedly. Had you done a compression test before opening it up?

Compression test was done, as stated in my above post. Across the deck it was 180, 90, 140, 185 with cylinder #2 having the worst valve pitting (lowest compression number.)

It doesn't matter because I'm replacing all of the valves and all of the moving engine parts with the exception of the pistons....I was curious as to why it did it.

I've asked a few engine builders over the past couple days and one seemed confident that the pitting is caused by the stem seals leaking and oil running down the valve, then burning and "sticking" to the exhaust valve. It makes sense, as the #2 cylinder in her car also had the most evidence of valve seal leakage.