1999 firebird 6cyl. one of my lifters is knocking and i can go about a

[anthony a]

mile and a half and it quits knocking? i removed the cover and found that the rocker arm will move about a quarter of an inch all others are firm. the rocker arm is not touching the rod. parts place gave me another roller but do i have to remove the head to replace it

 

[jcopie]

The lifter is leaking down. Replace the lifter. You should not need to remove the head to change it.