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MG MGB Technical - Dumb fuel question

I'm sorry for this silly question. I just bought my first MG, and I'm wondering what kind of gas to use. The owners manual says 91 octane regular LEAD gas. I just filled the tank with UNLEADED. What to do???
Brian

No need to worry. As long as your not racing your B, the unleaded fuel will have negligible affect on your car. And you never know, the previous owner may have already rebuilt the head and done the unleaded conversion. I put 45,000 miles on my 74B using unleaded fuel with the stock head, and didn't suffer. I believe the original softer valve seats take the abuse from not having the lead to reduce friction. Others more knowledgeable will respond if I'm wrong on that. When the MGB head gets rebuilt, it usually has the valve seats replaced with hardened ones that resist the unleaded fuel's destructive nature. You didn't mention whether you were using Premium fuel, which should have an octane rating somewhere near 91. If you are just using regular fuel and not experiencing any knocking or pinging, then just enjoy the ride, and put those few extra pennies in your pocket for some future head rebuild.
SteveO

Mine is an early 74 B. The previous owner just used unleaded gas but when I got it I added CD2 lead substitute with every tank. After a couple of years of driving, I noticed that the valve lash would get too tight. I'd set it, drive 100 miles, and it would be too tight, so I'd set it again, and in 100 miles it would be too tight. Finally a valve burned. The problem was that as the exhaust valve seat burned away, that allowed the valve to go higher into the head, making it seem like the valve lash was slipping.

the answer to your question is that if your car originally had a catalytic converter, then it's alerady made for unleaded. If it's earlier than that, you would be better off with a lead substitute or additive, or have the head professionally rebuilt for unleaded gas.
Ken Thompson

This thread was discussed between 30/10/2001 and 31/10/2001

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