[6pack] unleaded fuel

[John Macartney]

The UK finally banished leaded fuel availability in 1999. In the run-up to that event, there was a 
lot of panic (fuelled (no pun) by the Press) that unleaded fuel was unsuitable for classic car 
engines as a whole. This has proved to be bunk with cars that had cast-iron heads. At that time I 
was working for BMIHT and did a lot of research for enthusiasts prior to releasing a publication  on 
what they were supposed to do. The findings were as follows:

1. Cast iron head engines - even without hardened exhaust valve seats, create what is basically 
known as 'lead memory' - in other words, lead is absorbed into the cast iron rather like a sponge.
2. There really is no need to panic and fit hardened seats as all Triumph engines have proved to be 
exceptionally tolerant of lead-free fuel without hardened seats.
3. All that is needed is slight retarding of the ignition.

Of course, if you want to use an additive, potassium is widely held to be the most suitable as a 
lead replacement. To the best of my knowledge, the factory did not ever fit hardened seats to cars 
for North America, even though unleaded fuel was available there long before it was in Europe and 
the UK. With this in view, surely the factory would have been concerned about valve seat life where 
unleaded was widely available and IF it had felt hardened seats were desirable, I'm sure it would 
have fitted them for all markets and not just North America. My 2.5PI now has over 250,000 miles on 
the original head. It has certainly had new valve guides in my ownership but I thought I'd wait to 
see how it coped on unleaded without an additive. At 10,000 miles of hard driving, no sign of valve 
seat recession and I think it actually performs better on unleaded than it did on leaded!

My 2 cents worth

Jonmac