Hi Mike,
A little valve noise is not uncommon on these old engines. Especially at startup when cold, before oil gets fully circulating and parts expand due to heat to reduce valve lash. After a hot run, when oil is thinned a little due to heat, it's common too.
What oil are you using?
If not already doing so, I'd suggest that in summer heat you might want to use something heavier, particularly if your engine has some miles on it. Maybe 20w50?
Synthetic or non-synthetic?
Opinions vary a lot, but I personally prefer to use non-synthetic oils in these old engines and change it every 3000 mi./3 months minimum. This is the type of oil these engines were designed to use. Synth oil might make things a little noisier (plus can lead to more leaks, is expensive and often has too much detergent in it, IMHO).
Other causes/solutions for valve noise:
- Valve seat recession due to unleaded fuel. I think this is unlikely on a '79 car, but am not certain. Usually it can be spotted by frequent need to adjust, particularly the exhaust valves. The real/final solution is to rebuild the head with hardened valve seat inserts on at least the exhaust side, and use Stellite valves. Again, I'm not sure this is likely on your car, due to it's age.
- Weakened/soft/old valve springs. Again, head rebuild time.
- Worn rocker assembly: bushings, rocker shaft, etc. Pretty easily and inexpensively rebuilt without pulling the head from the engine.
- An oil cooler can help prevent oil from thinning under hard driving use and in high summer temps. If installed, it should have a thermostatic control, too, to prevent over-cooling at other times and to keep cold, thick oil from over-pressurizing the cooler at startup.
- Not a cause, but a possible solution: Install an aftermarket cast aluminum valve cover... muffles some of the valve noise... and it looks cool too!
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