Sounds like the rocker arm, cap nut and lock nuts need to come off to see what is the problem. It would be best to have a new cap nut and lock nut on hand. Also look for a taller hardened lock nut of the same thread in case the threads on the valve stem are damaged. The taller nut would use undamaged threads.

Pulling the rockers isn’t difficult, rather straight forward. Probably shouldn’t run it until this is corrected, could burn a valve or damage a cam lobe/rocker.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer