The problem is actually with the exhaust valve guides that are close to the EGR passages in the cylinder head. The oils that were used during that time had a nasty habit of "coking" (forming hard carbon deposits) in a hot spot, and the EGR passages definitely got hot. I've actually had to drive pushrods out of a buildup of hard carbon in that area. The drag on the valve stems and pushrods from the carbon deposits would wear out the cam lobes.
When General Motors announced in the mid-1980's they would not honor the warranty on any engine that ran 10W-40 oil, they never would admit that one particular brand of oil was causing problems. However, unofficially, the initials Q-S kept cropping up in off-the-record discussions with the engine instructors at the GM regional training center in Memphis, Tennessee!
Switching to Valvoline or Kendall oil after replacing the cam and lifters solved a lot of problems.
Jerry
Last edited by Hotrod Lincoln; 12/26/2008 6:42 PM.
