The valves need manual adjustment just like the diesels. If you hear a clicking from under the valve covers and the engine runs a bit rough then you will need to pull the valve cover and look at the cam and cam followers.

If they are gouged out then they will need to be replaced. If the lobes are still smooth but the followers are dished out then perhaps some new followers and a valve adjustment will be all it needs. But if a cam lobe is dug out the only cure is a cam replacement and this car has two of them.

When the engine is running if the exhaust sucks back now and then and I mean a big gulping suck then an exhaust valve is not seating like it should and is very likely burned.