I'm thinking lean and ultra-high combustion temps would be the root cause. overheating spark plug causes ceramics to break apart, then you have bits fouling moving parts, such as the valve. I'm thinking just a scored valve sealing surface might be enough for it to start leaking high pressure high temp gas on power stroke when it's supposed to be closed and the end result of that is that the scored area starts eroding - basically melting away, becoming a hole.
How'd the turbo and bore fare? presumably bits of spark plug and valve went through the turbo, and having things rattle around the combustion chamber is a horror story when it comes to mechanical sympathy.
Do you have instrumentation - i.e. an Accessport or similar? I would have expected knock retard values to give you a heads up. It can all happen pretty quickly though. A single quarter mile run melted a piston on someone I remember reading about.
I'm considering a garret GTX2867 and downpipe change for my BK a bit down the track - makes me think it will be wise to check injector flow health and be thorough about checking it's all up for the job - better safe than sorry.
Originally Posted by
onion63601
I'm not 100% sure what cause the valve to burn out, but my best hypothesis is that the engine went lean and detonation occurred in cylinder 2 and 4. The spark plugs were at the stock heat range, and the tips may have been glowing hot and caused the procelain to break off. In the case of cylinder 4, some the porcelain may have damaged or gotten caught on the exhaust valve seat on the way out, and cause the valve to burn out due to a gap created or holding the valve open. I got the injectors flow tested and they found that injectors on cyl's 2 and 4 were flowing insufficiently, so this may have cause those cylinder to run lean. It's all a very complicated tapestry of events, and thus its very difficult to diagnose...
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