Chunk blown out of my valve again, wtf?

[Binladin]

Anybody have any wisdom wit a chunk blowing out your valve?
A good chunk blew out my #3 exhaust valve(a6) last year so I rebuilt another head and put it on...
6 months later same thing happens to #2 exhaust valve(a1), grrr...

Is my bottom end screwed? It runs/sounds like a mean wrx atm and has just been sitting, I rebuilt another head recently but don't want the same thing to happen running my a6 head again.

[Fleetw00d]

Is it blown out, or burned out? What clearance did you adjust the valves to? If they are adjusted too tight, they may not seal correctly, allowing hot exhaust to leak by during combustion stroke, overheating/burning the valve. Lucky (?) thing is that gases are typically being pushed out past the valve (particularly during combustion stroke) so pieces would tend to go away from the cylinder. You'll be pulling the head anyway so you can check the pistons.

[92smokeaccord]

Did you cut or at least lap the valve seats? Chances are with out doing at least a lap job on the seats you got gassed past the valve and detonated which burnt and or blew a chuck of valve out. Need to have a good foundation with valve seats. Chances are even if you lapped them they were probably pitted some which would have required them to have been recut. Only way to know if your bottom end is good you eaither need a scope to look in and see what going on or pull the head. You have to pull the head anyway so I would just go that route.