Found some nice info about the valve train in the reference section! 
How is your oil pressure when the engine gets to operating temperature. One thing you can do is one by one remove a spark plug wire from the plug ends with the engine running. This can show you several things, it removes the spark load from that particular cylinder and if the knock goes away when a certain plug doesn't fire, then it is either the crank journal, wrist pin or cracked piston skirt... something going on internally for that cylinder. If the knock remains after you have removed all the plug wires one by one, then it is most likely a worn part in another area of the engine. Check your crank thrust(with engine not running), and things like flywheel or flexplate warped and contacting the bellhousing. Also check other rotating and moving objects outside of the engine(pulleys, fan,etc..) to eliminate obvious problems and wild goose chases before attempting to tear into the engine. Diagnosing a cam or lifter noise is a little more tricky, you might take a long piece of vacuum hose and stick it to your ear like a stethoscope, and put the other end on the valve cover and move slowly front to back and see if you can pinpoint if the knock is in the valvetrain(worn rocker, collapsed lifter, etc... ) or deeper in the engine. I've seen some Chevy 6's have a worn cam thrust plate and not give consistent knocking and be difficult to figure out, your engine might or might not have one so don't overlook any and all possibilities. Maybe this will help give you a starting point to begin with.
Bookmarks