MG Car Repair: petrol, tappets, unleaded fuel

Question
Hi Barrie, i`ve just recently bought a 1975 mgb gt 1.8. How do i know if the car needs additive, as i don`t know the last owner?
thank you,
Paul

Answer
Hi Paul.  I presume you want to know if your car will tolerate unleaded fuel.  Without removing the cylinder head, you cannot tell.  

I would set the tappets correctly and then drive the car using unleaded.  For the first few thousand miles, keep checking the tappets.  If the gaps are getting smaller, then the valves are receding.  In this case, either you need an unleaded head conversion, or you could just use an additive whenever you fill up with petrol.  If there is no recession, you can assume that the head has already been modified.