Senior Tech Team
Join Date: Aug 2002
Location: Gold Canyon, AZ
Re: Interesting valve failure
How bad beat up is the valve seat in the head? I have seen this failure if the seat is not concentric. Usually it breaks the entire head off but the break usually occurs in the first few runs. I would check the valve seats in the heads.
I don't think this valve failure was the result of non-concentric seat. As you have mentioned, a non-concentric seat will break the valve stem, just below the valve's head. This is due to the fact that the non-concentric seat is bending the valve stem back and forth as the engine runs which will break the valve stem just as bending a piece of wire back and forth will cause the wire to ultimately break.
I think this valve failure can be attributed to material problems/issues relative to the manufacturing process.
64 Chevelle Malibu Sport Coupe (original owner) car now has 427" BB, Jerico 5-spd. trans., Dana 60 rear end.
SAE Member (25+ years)
ASE Master Certified Engine Machinist
AERA Certified Professional Engine Machinist