Classic/Antique Car Repair/1977 Thunderbird
We've exchanged messages before. I wrote originally about a ticking noise coming from the engine, which you diagnosed as a sticky lifter. I have done nothing further in fixing it to speak of, but I did want to run something else by you. I've discovered that this sound is actually the lifter tapping on the underside of the valve cover (it makes no noise with the cover off), and it does seem to be getting louder as time goes by. But it is still gone within the first few minutes of startup. I've tried doubling the gasket, but it has made no difference, and doesn't address the problem anyway.
I suspect this may prompt an entirely different diagnosis from you, hence my contact.
Thanks for writing back. What you're describing is almost what I'd consider a mechanical impossibility: a metal to metal contact to the valve cover that disappears when the car warms up.
If you had metal-to-metal contact, it would be constant and loud, almost like a clanking noise that would not go away with warm up. But, to verify your description, I'd pull the valve cover, turn it upside down and carefully examine for any bright spots or scrapes indicating metal-to-metal contact. If so, look at the valve train components corresponding to the scrapes and look for broken valve train components, push rods, rocker arms, etc. This would not be lifters as valve lifters are resident in the "valley" beneath the intake manifold and are nowhere near the valve covers. And again, if the noise was due to this cause, it would be constant.
But, unless you're dealing with something really unique like the lifter and push rod assembly hyper-extending the rocker arms (which I'm not even sure is possible), you're back to the diagnosis of last time, a sticky valve lifter that harmonically sounds higher in the engine but actually is due to looseness in the valve train due to a valve lifter that is not pumping up adequately on cold start. Look online for the theory of operation of a hydraulic valve lifter. You'll see the important function that clean oil and mechanical wear has on proper operation. Lifters are actually small pumps and when the pump gets dirty or varnished, it doesn't operate correctly and has the effect of looseness in the valve train causing to the noise that you hear. The fact that the noise goes away tells you the lifter is not stuck too badly and should respond to either oil additives or direct application of valve cleaners to get it operating properly again. The growing intensity of the noise is telling you it's getting "stickier". Of course, if all the preceding doesn't work, lifter replacement is the next option but will take a lot of work as the intake manifold will have to be removed to access the lifters.
Sorry for all the detail but I felt you were at the point to know more how these things work so you can diagnose your problem. Please let me know, if you will, the results of your observations and tests. I can always learn from you too.!!
Best of luck,