1969 400 - Lifter Type Noise When Hot

[Firebird69]

Hi fellow Pontiac gear heads. I'm a new forum member and thought I'd connect with you to see if you have a suggestion to consider for me. My 400 was last built in 92, sat for 12 years before I bought the project car it was in. I've enjoyed it well for 10 years. My guess; has about 20k miles on the last build long ago. About 6 months ago, while going to a car show, I noticed a lifter type noise when she got hot. Not water pump. Not loose rockers. Screwed studs all level. I've been knocking off the easy stuff like; Seafoamed the crankcase since I thought sludge was the culprit. Put in Motormedic as oil additive in last filter/oil change. I'm using full synthetic Mobile1 - but doubt that matters.
Ever run across similar issue? I did with my 68 Bird in late 70's and needed cam / lifters. I'm guessing - but may be another top end overhaul.

Thoughts anyone?

 

[melsg5]

depends on which Mobil 1 synthetic you are using, if not the 10W50 version with sufficient zinc/phosphorus you may have wiped a lifter/cam lobe. It has been a known issue for a number of years that you can not just put in any type of oil in the older cars with flat tappet cams as opposed to rollers which all the new cars have. When it was built did you use stock valve springs or something stiffer? Go through each rocker on a cold engine when the cam is on the base circle for that valve and check for one that is obviously looser than the others.