160k knock

[robertn78]

I have a 99 Mercury Mountaineer / Explorer 2x4 with a 5.0. I am getting a loud knock at idle up past 4k RPM. (Don't want to blow the motor and test higher.) It has always had a knock sound at high RPM and under load, but more suttle. It seems to follow the RPM curve. It has 160k miles and have owned the car since 37k miles. I used a stethoscope, and found the noise is loudest on cylinder 5 in the center of the valve cover. Is it the lifter? What else should I be testing?

This comes after oil pan gasket change. I changed the spark plugs and added STP oil additive which had no change.

 

[robertn78]

After pulling off the valve cover and pulling the valves apart, I found that the Valve Retainer is 2 pieces. There is a huge amount of play between the 2 pieces. I will post after I replace the part.