Valve lash question?

Hi Fabo, need your help once again. I have a 340 small block with (273 adjustable iron rockers.) It has a crane .484/.484 hydraulic cam. I heard a little tapping and reset the preload on the lifters.

Cylinder 7 is the one I have a question on. I backed out the adjusters on both intake/exhaust. As I was setting preload, both screws only turned in a little and preload set too quick. The threads on the adjusters do not go two or three threads in. Preload was gone too fast, compared to all other cylinders.

I ran a compression check and that cylinder came back at 125, compared to all other cylinders from 160-165.

Just need to know what I should do now. This is all new area to me. Not running the engine, until I know it's fixed. Have been reading, it could be a burnt valve.

Any and all help is greatly appreciated. Thank you