Follow through with the forensics here. Pull that valve and look at its seating surface. If you do not determine exactly how the engine screwed up on you, then you will be beset with guessing and paranoia and generalized anxiety.Hippie wrote:I will thanks. (New SPs are NLA anyway.) I've had good luck with them too, actually unless I get a big vacuum leak.bajaman72 wrote:Search around for good/rebuilt ones. I have been finding pretty good deals and they seem to be working out okay.
It very well could be that a soft (at time of manufacture) seat made that clearance close up, which made it not close all the way which leaned out the mixture and gave you an effectively-only-a-three cylinder engine only at speed in the beginning phase when valve was hot and stretched, which then delivered you to a piston-seizure marks, etc.
Let me know your exhaust valve seat width. Below is Squareback January 2008
Initial Presentation:
Normal Seat Width #4E
Abnormal Seat Width #3E