Hollow sound, top end. Lack of oil? Rubbing?

Strange title, I know. Strange happenings. SO, after having idle problems, a sound developed in the top of the motor. It made the motor sound hollow, as if there were no oil in it. I knew there was, had put in new oil and filter. But I dropped the pan anyway. Found a half a piston ring. We all decided it had been broken from installation. So off somes the head and jugs. Rings replaced, new gaskets. Motor goes back together. Still this hollow sound. Now, as of yesterday, I've dropped the pan and replaced the oil pump as I had a working spare. I haven't put her back together yet, but the old pump really looked good. No crud, sprocket good and so on. One thing I noticed when I pulled the head, was that on the #3 intake cam lobe, there was no pool of oil as in the other lobes. I'm wondering if this could be the culprit, and if so, because I only play a mechanic...where the F does the oil come in for that, so I can see if something is clogged...OR...suggestions are welcome.

umm ,,what kind of bike are you working on?

Thought it was in the signature, my bad

1993 KZ1000 police

pull the lifter/bucket off the spring area and look down the hole

if you don't replace the two oil pump o-ring gaskets you will lose oil pressure.

there should not be a pool of oil in there. the drain hole may be pluged.
the oil comes up through the cam bearing, seeps out around it ,then drips down to oil around the bucket.