What's the history of the engine? You said stock cam and lifters, but it sounds like you have aftermarket heads?
What year and model engine, and how many miles?
What do the old lifters look like on their bases? You said some were questionable, but in what way?
What heads are you running?
And maybe most importantly, when did the noise start? Did it happen right after swapping heads, or has it done this all along since you've had the Bronco?
Paul
its a 2000 ford 5.0 out of a ford explorer, the valve train was tired from the engine having around 140k on them. I picked up some cheap flotek 1.94 intake 1.55 exhaust aluminum heads thinking they would be comparable to what I pulled off.
the roller of the lifters looked fine on all, three lifters seemed like they would bleed down fairly easily, I was able to compress them a little just by using my finger, the rest stayed solid and I couldn't compress them by hand even using a pushrod in the cup.
the noise started with the new heads, before the valvetrain was a little noisy but not too bad.
today I pulled out the spark plugs and snuck a camera inside the cylinders and was unable to see anything out of the ordinary, not nuts dropped in, no contact marks, nothing.
To me, it sounds like something is hitting, it is loud, way louder than it should be. I can not find signs of anything hitting though.