1984 Nissan 200SX Ticking and Stalling

My car has started to stall at random moments, either idling or driving. The engine cranks over but won't start. Usually all it takes is 30 sec of rest till it starts again.

What I have noticed though is when it won't start, the key is in the "on" position and a loud ticking is coming from the cylinder head. The ticking continues at half second intravels until it stops, at which point it sounds like some pressure or liquid is released for 2 secs. As soon as the ticking stops, the car starts right up. Please help