First let me say that I'll definitely investigate that possibility before I pull the motor. Removing the head is a lot less work of course! And I will verify the valve moves freely on its own before going too much further... ...But keep in mind I've had the valve cover off and played with this. It's pretty easy to tell that the tappet sticking is what is happening here. It doesn't want to rotate very freely even when it is not under load from the spring and when the valve is down. Trust me, I know it's hard when you can't see it for yourself, but the tappet is sticking in its bore. All of the other 3 tappets rotate/spin easily and move easily in the bore. This one does not. You can get it to move with a wrench, but not with your bare fingers. The spring rotator is very free, it's fine.