I've got a 97 f150 170k miles got it from my mother in law two years ago with cylinder 6 head gasket blown fix it all up been driving it runns great just did manifolds o2 sensors egr and tube. I've noticed a tap from top of the engine it's constant never goes away and follows the engine rpms. It's getting louder over time I'm just looking for ideas before I take it apart. Any help would be great thanks.

 

Something you might try,
Take a piece of garden hose or any kind of hose and with one end placed next to one of your ears, move the other end around the valve covers and see if you can determine which side is loudest, then remove that valve cover and with the cover off start the engine for a few seconds o see if one rocker arm is /appears loose. It could be a plugged lifter or possibly a cam problem. You can use the hose trick to pin down which valve might be loose, providing it is a lifter /valve problem.

 

I'll have to give that a try. I'll post more as I look into it. though as to running with the valve cover off I think I'll just roll the crank pully with a wrench and check. if I can figure out how I'll post a vid of the motor running.