Originally Posted by MouseFink
The O-ring groove was eliminated on the 1996-2000 062 and 906 Vortec valves and a different retainer without a shield was used.
The 906 Vortec heads were equipped with hardened exhaust seat inserts which resulted in a increased valve seat margin compared to the intake seats. The increased exhaust valve margin made the exhaust valve sit lower in the head. It was corrected by making exhaust valves with longer tip lengths. The keeper groove was the same distance from the valve seats.
In order to maintain equal valve stem heights , the O-ring groove, O-ring seals and oil shields were eliminated on the Vortec valve stems and the retainer lock grooves were relocated. The tip lengths were changed from .250" intake and exhaust to .289" on the exhaust valves and .260" on the intake valves. The valve face and seat angles should be ground in order to establish the valve margins at .050" intake and .080" exhaust to allow for the difference in valve tip lengths.
Thanks for the info, I have not seen this tip/seat info here previously. If it can be verified (not doubting you; got any links?) I will include it in the wiki
My heads are 062 w/induction hardened
exhaust seats. It may be that standard Vortec tip valves were used in non hardened insert Vortec applications; there's no sense in using a too-long tip to correct for a problem that doesn't exist on non hardened insert-equipped heads- this would be as bad as using a too-short tip on an insert-equipped head.
However I believe discontinuing the O-ring/metal shield was unrelated to going to a single groove stem; the O-ring/metal shield simply isn't needed when using the Vortec valve stem seals. I believe they opted for the better seals for emissions and cost savings as much as anything, secondarily for any other reasons.