Rotating exhaust valves

I've posted it elsewhere, but the 4-groove exh. stem locks are in a rounded-bead form with matching grooves, and as correctly stated above the locks "butt" together before they can grip the stem. This is a simple rotator system, and will allow the valve to turn when open. When I install serious valve springs using these, I grind one side of each lock half until they have a decent gap, and a solid grip on the stem.
C'mon RRR, You've never seen a circular pattern on a valve-stem tip before? I'm not sayin' to bank on it's function, but they DO turn...whether rotators were worth it or not, only engineers & fleet feedback can probably say.
All that said, if those J head valves are turning on the seats, good chance they're 340HP's that need shimmed or replaced. They have a decent rate, but low seat load(~70#) when the height is correct, little tolerance for too much installed ht.