my son recently purchased, started making clacking (lifter?) noise when cold, is now much worse, and constant. have tried heavier oil, lighter oil, engine flush, engine rejuvenator, just checked timing alignments both cams lower crank gear. all ok. I fear bent valves or worse. Got any ideas?

I would guess your problem is the lifters. To really help, you'd need to remove the lifters and clean them manually. You could also buy new lifters if you don't mind spending a lot of money. But having the lifters cleaned should help your with the lifter noise. Always use the recommend amount of oil and the proper weight. Keep an eye on the oil level and be sure you're not leaking or burning any.
Good luck!