General Tech Damaged Valve Lifter TR4A

I think I found the source of my constant tapping, despite repeated re-setting of the .010 clearance. One of my lifters, valve 5, is really smacked up bad, with a very noticeable concave underface. Another lifter is knocked up a little but not much.

The lifters were new in 2004, and since then only 20,000 miles on the car.

I do not believe I did a proper cam break-in back then.

What would cause one lifter to be so damaged? I'll replace the cam, of course, but I'm concerned the pocket where the lifter sits may be damaged, or maybe the cam bearing in that area.

Does this happen sometimes just do to unpredictable binding in the slot? Should I just replace the lifters and cam and go back to driving, or do I need to pull the block and get more serious here?

When the cam is out, install a new lifter in the bore and ensure it goes in, out, and spins freely in it's bore. To wear properly the lifter must be free to turn easily. After that don't worry about it. Dealing with some of our repro parts, I am convinced that we occasionally get parts that are not properly heat treated. That would make it no fault of yours.

There were a rash of bad lifters going around just about the time that you installed yours, but they seemed to go sooner than 20,000 miles. I know that the lifters I got from BF&E sometime around 2008 were all tested for hardness. You could see the tiny divot in the lifter.

Not seeing a photo...but..if the lifter is dished out on the surface, the camshaft is now shot.
It will have the same contour as the lifter.
Sorry.

Had enough bad lifters/flat cams come through the shops in my life. If the lifter has dished, it's taken out the lobe.