I have a noisy lifter in my motor home. 82 Chevy 350ci. I figured its time for a cam and lifter change so i changed cam, lifters, and timing chain. The old cam was good and the lifters came out easy. The same lifter is still noisy #8 exh. I tighten it a bit and the rattle is gone. A few seconds later its back. There is oil coming out the push rod, oil pressure is good at 60psi. I tried another rocker arm, same thing. Why is this lifter not pumping up?