Unleaded Stag

[martinstag]

Unleaded petrol was introduced in the USA in the 1970s, as was the Stag. Since the Stag was aimed at the American market, is it possible that the Stag engine was built to run on unleaded petrol?

[bullstarz]

Well as one of the few things on the triumph stag that is actually aluminium is the cinder heads. As a result the cylinder heads all required Steel valve inserts. Whereas it possibly wasn’t designed to work with unleaded fuel, the fact that you have hardened steel valve inserts would make it acceptable to use unleaded fuel.

[StagJonno]

I think there's a reference to this in the Kingpin articles, accessed from the main SOC site. From what I remember, someone was in contact with the engine designer who said that the valve seats were suitable for unleaded petrol. However, ISTR hearing that there were valves made from different materials - one was definitely for unleaded though the other didn't perform as well. So, I'd suggest you don't worry about it too much, though if replacing valves, make sure you get decent ones for unleaded (speak to Peter at LD Part).

A lot has been written about lead replacement additives. My conclusion was they weren't effective, so I gave my stock to another classic enthusiast who was following recommendations from others in his club.

[Roy_S]

If the valves you have in the engine are the type that are not unleaded friendly they would need to be replaced anyway, and as these are the part that would burn/wear out after some 20k plus miles of high speed driving, I wouldn't worry about it until then.
I'm in the same boat, I know the heads were worked on some years back, don't know what the previous owner specified or was sold, and not going to pull apart a working engine that is showing no signs of that problem.

[jbuckl]

Standard stags will work fine with unleaded fuel.
Harder valves / seats are available, but not essential.
Imho super unleaded is best these days … avoid high ethanol fuels…. main reason is boiling point is too low for carburettor cars.