Agree with Ruairidh I have never used anything but unleaded in my standard A7's since leaded left the forecourt and have not noticed any ill effects.In the S/C car I do put in Tetra Boost with Shell Optimax high octane fuel to counteract the octane derating of the Castrol A747 S/C lube to give 100 octane fuel.Tetra Boost will also convert non leaded to leaded.

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I used Valvemaster for a period, but found that I had to stop and clean the jets about every seventy miles. There was some sort of gunge manifesting itself in the main jet. This happened probably half a dozen times. Stopped using it and the problem went away.

I do agree, however, that there are very good prices available by dealing directly with Castrol.

Mike

I didn't use additive until I rebuilt the engine a couple of years ago, and replaced the valves & guides and had the seats recut. I do now, but I don't think I need to, it's just "belt & braces". I don't think you can do any harm in using it even if it's not necessary.

There was no leaded petrol until circa 1935, by which time most of our cars had been made.QED.

I'm pleased that the discussion is active and am interested to hear other owners views and experiences regarding these type of additives. I understand that during the period when our cars were built that it was very common to strip the engine down every 3-6000 miles due to the very poor quality of fuel.

I've just done 1000 miles in a 1938 Pearl with no problems, nothing bar fuel from the pumps, if you look in the handbook of the time it mentions leaded fuel in a way that suggests it's nothing to worry about as a new fuel and can be put straight into a car (thus suggesting the unleaded fuel used previously was considered the norm)

David, I have been doing 5000 miles a year regularly and over the last 15,000+ miles I have had no problems. I do not use ANY additive, not even Redex.

If you do the research on the internet on Valve Seat Recession you will find that there is no problem at all with engines reving up 3000 rpm, just a slight problem at 3,500 rpm and then an accelerating problem for engines reving at 4000+

AS most of our engines will be running at 3000 rpm or less for most of their time there is no problem.

Indeed, trying to fix a problem that doesn't exist causes others. Carburation blockages is one. I am not an advocate of hard vale seat inserts. They have their own problems as well. Unless the junction of the two metals is perfect ( the block and the insert ) then you create a thermal barrier which creates a problem of inadequate cooling that didn't happen before.

My advice is to leave well alone. Use the car with no additives and no hard inserts. The valves are closed long enough in use for the heat to transfer from the valve into the block and away into the cooling water.

Unless you have a blown engine pulling 5000+ rpm you ain't got a problem!

Many thanks for interesting debate, I will stop using the additive this season for two reasons, following advise here and my engine requires an rebuild which I hope to have done in Autumn.
As an aside I also use the additive in my OHV Meadows engine (1925 vintage) please excuse the 'its not an 7' on this occasion, I do wonder now if I should give up using the stuff in this engine?