Sequence One Most cars built before 1981 and many built before 1986 were designed to run on leaded petrol.The lead in leaded petrol acts as a solid lubricant, between the exhaust valves and the soft exhaustvalve seats that these older cars have. Sequence Two When these vehicles are operated to prevent the valve from recessing into the cylinder head.on unleaded petrol, exhaust valve seat recession (VSR) occurs.That's because VSR can cause valve burning and loss of performance and,if allowed to go unchecked will ultimately resultin loss of compression and engine failure. Sequence Three Valvemaster acts as a solid lubricant in much the same way lead does,without any loss of performance.