pull the valve covers and be sure that the return holes for the oil are not all plugged up, this is a real concern. if all is clear, check for a loose rocker by following the firing order 1-8-4-3-6-5-7-2. when the valves are closed you try to turn the pushrod with your fingertips, if you can, tighten the rocker 3/4 turn (i like to use a 1/2 turn) AFTER THE INITIAL FRICTION of the rocker and pushrod, this is the method i have used for years and have never had a problem. if you have to change the lifter it is easy and they are cheap. buy a whole set of lifters and pushrods, it is easier than doing it again. summit racing sells them as a whole set, cheap as well as advance auto parts, i dont like the autozone stuff myself but it is available.

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2003 audi A6
2002 porsche boxter
1989 jeep grand wagoneer
1987 m/b 420 sel
1966 vw type 1
1965 mustang "a" code gt