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MG MGB Technical - how much lead is required

how much TEL (tetra ethyl lead) is required for MG engines? OR How many milliliters of TEL per gallon used to be in leaded auto gas back in the 50's, 60's, and 70's?

Thanks,
Steve
Steven J. Korotky

Steve. It is unlikely that anyone here will be able to answer such a question. We are, for the most part, a bunch of good old boys and good old girls, not petroleum engineers. We have learned by reading, doing, asking questions, etc. and try to pass on what we have learned. There are, however, certain questions which require a specialist to answer. Such as "how thick is the casehardening on the rocker arms?" or how much lead is required for an MG engine?

Back when they made leaded fuel, there was sufficient lead in the fuel to allow the valves to function as designed. When the switch was made to unleaded gasoline in the US, the valve seats in the cylinder heads were induction hardened to allow proper functioning without leaded gas. There has been some research that indicates that the older cars, with the unhardened heads, which had been run for a number of years on leaded gasoline would continue to run correctly when operated on unleaded gasoline. I have been running my 68 GT for the five years I have owned it with no problems using the unleaded gas. The compression has actually improved since I bought it (it is a daily driver) and the valve clearances are showing almost no change over the years.

Where there does seem to be a problem is when one of the cylinder heads without hardened seats goes in for a valve job. Cutting the new seats seems to remove whatever protective coating had built up over the years. Thus, an "unleaded conversion" must be done, installing hardened steel valve seats. Any competent machine shop can do this. If you want other performance improvements, both Peter Burgess, in the UK, and Mike Brown, in the US, provided excellent work. Les
Les Bengtson

Yes, but some of us are chemists.
Without getting into the debate about how wrong it is to release unadulterated lead into out environment (and how I wouldnt want to synthesize TEL in my garage anyway), in the 1980s, tetra ethyl lead was used in decreasing amounts and was hovering around the 1.3 gram/gal mark, so one can only assume it to be slightly higher during the 60s and 70s.
Ive used lead additives and been fine with them thus farI would just suggest whenever you get your engine rebuilt, have the machinist set you up for unleaded use (i.e. use hardened valve seals).
By the way, for those of you who care, apparently MTBE is on its way out, too. It really doesnt seem to reduce the amount of CO produced and its contaminating ground water supplies left and right.
Ethanol seems to be the replacement additive of choice, but it is not without issues, too.
Eric.
Eric King

Steven,
Based on empirical evidence gathered from a population of exactly one vehicle --- none. When I got my '69 B in 1995, I had the valves ground and the seats cut as one of the first things I did (it needed a head gasket and valve work. In fact, that's why it was parked in 1980.) At the time I didn't know or didn't think about hardened seats. When I learned about hardened seats later, I decided to not worry about it until I started seeing valve recession. It's now 2003 (almost 2004) and nearly 30k miles later, and no valve recession.

My advice would be that if you're doing head work, put in hardened seats -- for peace of mind, if nothing else. If you're not doing head work, don't worry about it until you do the head, or you start seeing problems. Of course, I am not an engineer (at least not that kind...), YMMV, #include <std_disclaimer>, etc, etc... ;-)

HTH!
Rob
Rob Edwards

It is considered that 0.03 g Pb/l is the absolute minimum to protect against valve seat recession. Tests have been run with this concentration on BMC series A engine which confirm confirm that finding. Most European specifications for leaded gasoline required a minimum of 0.05 g Pb/l.

The maximum lead concentration in USA was 0.84 g Pb/l until 1st July 1983 when it was reduced to 0.22 g Pb/l. The actual average value was closed to that maximum.

This is to reply to your question for a documentation point of view, because it is unlikely that this can have a practical application nowadays, tetraethyl lead being not marketed in your country. If by chance, you can find this material, it highly recommended to disregard it because it is highly toxic by inhalation and by skin contact, and it must only be handled by skilled operators in confined environment.

Jean-Marc Thély
JM Thély

Un-frigginin-believable!

The scope, vastness of expertise, the folks signed on to this BBS!

Almost an "Anything you want to know" place to drop by and pose a question!

Thank you chemical guys -- and everyone else-- this cyber space is quite amazing.
I, for one, am very grateful.


glg
glg

Well, here is the main point of the question. I'm a pilot and know serveral people that run maintainance shops, and when a plane comes in for major work, all the fuel is drained. This drained fuel can not be put back into aircraft and is used in all types of small engine machines around the airport using airport transfers tunbridge wells. Since not too many engines like all the lead in Avgas, they cut it and therefore it takes a long time to use it up. The last plane that was in was a stearman and they drained closed to 100 gallons out of it.

I've been told that 100LL (low lead, don't let the name fool you it just means it has less lead then the fuel it was designed to replace) has more lead in it then car gas ever had. I know that 100LL has 2.00 ml TEL/U.S.gal. Its looking attractive because I could problably get it cheap, it has a minimum motor octane of 99.5 and a performance rating of 130 octane. however, I don't want to cause fowling of the plugs or other problems due to too much lead, so I was wanting to cut it with high grade pump gas.

Thanks for all the information, but I need the amount of lead in ml/gal, as I don't know the density to convert the grams to ml.
Steven J. Korotky

The density of TEL is required to obtain the value in the units you requested. I can do that for you if you'd like, I just can't seem to find the value right now.
I tried the calculation a couple times with just the density of lead-- you can't get the right number doing it through that method... I now know that.
I'd have to get the number at the labs.
I'll try and get it today,
eric.
Eric King

The lead content of 100 LL is 0.55 g Pb/l. I let you doing the calculation for USG. As you can see the is no risk of fouling the plugs. The only risk with avgas comes from its low volatility which can cause difficult cold starting.
JM Thély

Our numbers don't seem to be working out too well (then again, it's like, seven AM, the err could easily be on my side).
Our numbers don't seem to be working out too well (then again, it's seven AM, the err could easily be on my side).
My value for TEL is .173mL/L [or .786mL/gal] (using a density of 1.653g/mL for TEL and a conversion factor of 4.55L/gal) and JM's is .133mL/L [or .606mL/gal]. They're close, but not dead on.
Using the same values for density, volume conversion, and the value of 100LL given by Steve, I get a TEL content of .73g/L which doesn't quite match JM's value of .55g/L.
However, if you take JM’s value to be true, it gives you a concentration of 2.50mL/gal, therefore, I'm assuming one of us has a unit that's been overlooked (example: one of our values is grams of lead per gallon of gasoline instead of grams of TEL per gallon of gasoline). Regardless, due to their close proximity, I would accept an average of my value and JM's low value to give you an acceptable minimum concentration of .153mL/L of TEL in gasoline (which, in Steve’s units, works out to be .696mL/gal).
This is where my expertise runs dry (not the field I'm in)... I haven't had to do a calculation of this variety in years... but... if you wanted ten gallons of gas in the above concentration, it would require somewhere around 25 to 40 gallons of straight-run gasoline per 10 gallons of TEL to make the dilution using the different values given by all three of us. That 15 gallon difference allows for a huge margin of error, therefore, it would require more definitive values to do this properly.
However, I would accept JM’s values to be the correct ones—they seem more spot on, therefore, I’d say it would take 36 gallons of straight-run per ten gallons of TEL gasoline to achieve the desired concentration.
Please... feel free to check me on this, I'm a little rusty and it's a little early. The most common pathway for error (at least in my experience) is human, especially when I’m behind the calculator.
eric.
Eric King

Eric,
Have you work out the lead content of TEL? This is 64.06 % weight.
Now we can do the calculation:
ml TEL/l : 2 / 3.785 = 0.528
g TEL/l : 0.528 x 1.65 = 0.872
g Pb/l : 0.872 x .6406 = 0.558
JM Thély

See, I knew there was something missing. I haven't had to do any percentages by weight or volume since I was in high school.
I was on the right track, just a back road.
Thanks for the help on that.
eric
Eric King

Steve
As a fellow pilot and MGB owner - Hello. I run my 1972 UK spec MGB on unleaded without any modification. Slight pinking under heavy acceleration is the only penalty. Here in the UK where we have a Socialist Government which taxes everything that moves - especially anything with 4 wheels - we have to use the cheapest fuel we can.
Iain Hallifax

My 72-built, 73 model B runs very poorly on standard unleaded, both heavy pinking and running-on (before I fitted an anti-runon valve that works). I had to retard the ignition 2 or 3 degrees which had a significant impact on both performance and running temps. Using Valvemaster with the so-called octane booster did nothing, whereas super unleaded including Optimax and LRP perform the same as leaded 4-star. I know we as individuals are reportedly going to have a tax on our very existence in a few years if we choose to move to the Job Centre, Hospital or air or sea port but a bicycle is still tax free, especially if you buy second hand.
Paul Hunt

Thought you paid VAT on a bike?
Matthew Crabb

Try this guy, he sells a product called Max Lead 2000 which is TEL. i have used it for several years in my 1963 Lotus Super Seven Cosworth (only offroad of course!).
Jack Podell 219-232-6430
Tony Bates

This thread was discussed between 12/11/2003 and 15/11/2003

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