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MG MGB Technical - Unleaded fuel?

I've just bought a MK1 mgb roadster (built in Oct.65).

Can I use unleaded gas without any additive? What grade should I use.

The engine was rebuilt by a previous owner sometime around 1975, I believe, but I have no idea what work was done to the head.
W.D. Lamprecht

Changing the valve seats to a harder style for use with unleaded fuel wasn't common practice until very late in the '70s when leaded fuel was becoming harder to find. Chances are good you have a leaded head and should not use unleaded fuel until proven otherwise.
Jeff Schlemmer

That's a bit harsh, how common is leaded now? At least we in the UK *can* buy it from selected pumping stations. If you want to err on the side of caution then use unleaded with an additive that protects against valve seat recession. But statements reputedly from BMW have claimed that an engine that has done at least 40k on leaded fuel and not had valves replaced or seats recut has enough lead leached into them - lead memory effect - to last the 'normal service life' of the engine, whatever that might be. Tests in the UK indicate that engines that are used frequently and consistenly for high-speed and heavy-load use become much more susceptible to damage than lighter-use engines. Finally North America has been unleaded for dozens of years, from what I can tell modifying heads for unleaded is not that common, and neither is recession.
Paul Hunt

"Thats a bit harsh" Having been in the auto repair bussiness for long enough to have seen the lack of bad things coming from unleaded, I say HERE, HERE! American Oil always [from about 1950] had a premium unleaded and it was a big seller and it was never blamed for head destruction.I ran an A with the original head on it for twenty years, most of it on unleaded and when I sold it,it started and ran as well as it did when I dragged it out of a shed in the 70s. My advice has to be, unless it is coming apart anyway don't take it apart to "unlead the head" Ric
PS has anyone personaly taken apart a head that they felt was hurt by unleaded gas? If so give real details no "I once heard" stories please. RIC
R E L Lloyd

I drove my A Series engine about 50,000 miles on unleaded fuel before I had it rebuilt. The first 120,000 miles had been on premium leaded fuel.

Although the effects of the driving on unleaded were only slightly noticeable when the head was torn down, I had it rebuilt as a "no-lead head". This is reasonable insurance against premature valve or valve seat failure and after rebuilding, there is no residual lead "cushion" left.

My conclusion is "drive it until it drops" on unleaded and then rebuild the head for unleaded fuel.

Modern fuels seem to be quite different from the leaded fuels the cars were designed to run on.

Ethanol attacks brass carburator parts and is a manditory additive in some parts of the U.S. which impose "oxygenated" fuel programs during the winter months. Even "summer" fuels seem to be more suceptible to vapor locking or rough idle when under the hood temperatures are excessive.
Glenn

Adding to the case, I ran my '67 with unleaded for 12,000 miles and when I tore down the engine to do the piston rings the head was fine. The worst that may happen to the head is that the valves will wear, meaning a recon head change is required, which is exactly what you will have to do to get an "certified" unleaded head right now. I'd just run it.
More importantly, make sure that the ignition timing is set for whatever fuel you are using to avoid pinking and use the highest grade you can for the same reason.
Steve Postins

So with that said about lead, how about the same situation except with the valve seals. Should you replace the stock seals with the Chevy Truck (Forgot The Part Number) seals or leave the stock ones in? This car has been sitting for about 6 years and the compression checked OK. I put the Chevy seals in my 65-B three years ago with great results.
Thanks
Steve C.
Steve C.

I'd run it on 93 octane unleaded, forget about additives and only redo the head with hardened seats when it was due for a valve job. There have been other threads on this subject, and there was a lot of talk about lead "memory", where an engine was previously run on leaded, there seems to be a residual effect that continues to protect. I am currently driving an MGA with lots of miles on the engine, and the last rebuild on the engine was at least thiry years ago. It's been running just fine for a few years now, on hi-test fuel..with no problems.
R. L Carleen

Ok, maybe I came off wrong, but I've always been the one to err on the side of safety when giving advice to others. It would be a mistake to say "yes the head was converted for unleaded use" or that running unleaded fuel with no additives will not cause any damage. Chances are good that W.D.'s head does not have hardened seats and it would be adviseable to use an additive with unleaded fuel, no matter what the octane. It doesn't sound like an engine rebuild is in the works, so why temp fate? It may or may not matter, but what if...?
Jeff Schlemmer

Leave it alone until it dies. You'd be surprised at how long it will last.
Mike MaGee

I had no idea this subject was so controversial. Thanks for all your advice.
W.D. Lamprecht

I was in a similar bind with a 78B rubbernose, replaced engine, unsure what the owner had done to the engine.
After a lot of investigation (most of it done here) I decided to use unleaded but under the assumption that the engine wasn't modified for it. As such I added FlashLube to the tank whenever I filled up, and eventually installed the FlashLube system under the bonnet to save me the trouble.
I then spent a lot more time and effort tuning the carbies and replacing the distributor insides with a Lumenition Magnetronic to ensure perfect timing, etc. Once I'd made sure EVERYTHING was as close to perfect as possible, I noticed performance was a touch better when I turned off the FlashLube tap. By this time I had a mechanic take the valve cover and head apart and during the process he noticed the valve seats and other modifications generally suggested for MGs wanting to run unleaded. I guess that's why it was happier to run without the FlashLube.

The only thing I can add with absolute certainty is my experience with the different octane ratings. If you're going to use unleaded make sure you use the highest octane rating you can get. In Australia we have both regular unleaded and premium unleaded (as I'm sure they do in most countries) but not all premiums have the same octane rating. Only 3 brands here supply 98 octane as their premium, the rest supply 93 octane. Regular unleaded is only 88 octane. The extra cost for premium has been easily paid back in the extra mileage I get, every tank.
D O'Brien

This thread was discussed between 17/01/2004 and 21/01/2004

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