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MG MGB Technical - Uleaded gas in an old MGB

I just bought a 1970 MGB that needs a head gasket. Here in California unleaded is my only choice. What are people doing about running unleaded gas. Are you just running it and not having any problems? Do you run an additive? Should I get a latter model head that ran with unleaded? thanks for any help Matt
wastingmoney

Matthew, I've used CD2 lead substitute in my 74B for many years now. Its inexpensive and convenient to use and available at Kragen. I've never had the head off my engine after 105000 miles. Maybe its not necessary but it hasn't hurt anything either. Bob
Bob Ekstrand

Matthew, The previous owner had used CD2 in my 72B and I continue to use it, just turned 97,000 miles and still no head problems, eventually, when compression drops I will have the valves and seats replaced and have the head ported, but for now it still runs fine and I'll spend money on other parts of the car. It may not have needed a lead substitute but we will never know for sure, and it is cheap insurance.
Joe

I've always been told that a general rule of thumb when replacing a head gasket is to take the head to a machine shop and have them run it though a milling machine, taking off only enough to make sure that the head is perfectly flat. If you have a bad head gasket, it may have been caused by a warped head, or the blown gasket may have allowed the engine to overheat, causing a warped head. Either way, it is a good idea to insure its flatness.

While you have it off, you might as well have them do a valve job and replace any burned or worn valves. Do the oil seals as well. Welcome to the "might as wells" that afflict us all who are trying to work on these cars.

A couple of years ago, my Buick Skylark blew a head gasket. I took it in, had it checked for cracks, the surface milled and a valve job done. It cost about $150. I did not need valve seats or any replacement valves.

Once you are in this far, it is not much more expensive to have the machine shop insert hardened exhaust valve seats. Once this is done, your car will have been fully converted to run on unleaded gas, with no risk of valve seat recession.

All that said, there are some who feel that a car that has been run for years on leaded gas can run unleaded for quite a long time without damage.
Paul Noble

I just filled up my new '67 mgb roadster for the first time. The other owner said to put the highest octane gas in it. Do I need to stop first thing tomorrow and buy CD2 (whatever that is)?????
Thanks for answering all my questions! I'm really sounding good when I talk to people about my new car!

Margo
Margo Lubbers

Margo...There are quite a few lead replacement additives available from the local auto parts stores, CD2 being one of them. If you can, ask the previous owner if they converted the head to run on un-leaded. Most "B" owners do add an additive every time they fill up. You should use the highest octane you can find for the "B".
Steve
Steven Brooks

I agree with Paul--if you'er pulling the head for a new gasket then by all means have the head rebuilt for unleaded gas by a reliable MG shop. Then you will definitely know about the condition of the head. It's better to get it done right the first time so you're not pulling the head next year too.
Margo, if your engine has good compression and is in good general condition, you should certainly try CD2. But that didn't work on mine, I still got a burned valve. You should be able to find CD2 lead substitute at local "parts houses" (I lived in OK for a few years and learned the local lingo!) like Western Auto or Auto Zone.
Ken thompson

None of the MGB heads ever produced were compatible with unleaded fuel. That even goes for those models sold with "unleaded fuel only" stickers attached.

What happens on a stock head when lead is not present in the fuel, is that the exhaust valves, (and often the intakes if it's high mileage piece)will "sink" into the combustion chamber. This causes a distinct reduction in the gas flow capabilities of even a stock head, and will change the valve lash over time if it's not checked properly. It also lessens the spring rate which isn't probably too big a deal if revs are kept in check, but it happens none the less.

The cure for all this, are special hardened inserts...or a ton of lead additive on a regular basis. You might consider what the lead additive will cost you in the long run and then price it against a proper seat installation, you may find it's cheaper to do it right.

Sean
Sean Brown

Wast, Bob , Joe ......

THere is some think I don't andestand about all those quetions about unleaded fuel.

1: lead was introduced in fuel during the 50th to prenvent auto firing so you can increase compression without using an very hight octane fuel
2: what about pre 50th engine that never used leaded when new.Die they will have to detoxification treatment after using lead for several years ?
3: (the more important) lead is replaced by bezene (french word can't found the english word for it) wich is much mor toxic for lung and can generate cancer .

The général opinion here is that the only thing to do is to use high otane fuel to prevent pigging on high compression engines and that all lead replacement product sound like spams or money makers .
An old french engine that had used unleaded for 30.000 m did not shown any anormal things on the valve seats and was much more clean .

Pierre
Cinquin Pierre

This is a very good article for those of you who have questions concering leaded and unleaded fuels.

http://www.pumaracing.co.uk/unlead01.htm

-Jared
Jared Snider

Have any of you that have used lead substitutes like CD2 noticed deposits on the valves and spark plugs? I acquired a '72B last summer and pulled the plugs, platinum with less than 5000 miles on them and noticed a reddish brown deposit, wasn't sure if that was from the use of lead substitute.
Joe

I've heard the argument made that lead was used in such large quantities in gasoline that the valves in most engines are so thoroughly impregnated with it that wear is not much of a concern. Thoughts? I know that I haven't seen much valve recession (based on checking rocker clearances) despite the fact that I don't use lead substitutes. I'm at about the 20K mile mark on my ownership of my B (clock shows ~110K...)

Of course if you're doing a head job with new valves and freshly cut seats, I suppose all bets are off....
Rob Edwards

The general rule of thumb around here, as I understand it, is to use high octane gas and be merry. I've been doing this for about 4 years now, gosh I'm old, is this wrong?
David Ryzuk

Anyone who doesn't believe that valves can recess into the head can just post "I" in this thread and I'll be more than happy to send you a multitude of photos of various heads we have seen where the valves are flush, or even below the surface of the combustion chamber. That is, the face (flat part on the end of the valve) is actually recessed into the head so far that it has to lift the margin width (or more) to be able to breath. It happens mainly on the exhaust valves, but I've seen intakes with this affliction as well.

Hell, I've even seen "valve jobs" where the shop in question did this for a customer, unknowingly and at no additional charge!

Sean
Sean Brown

Sean, my 74 did exactly what you are describing even with CD2 additive. Every 100 miles I would notice the valve lash was too small and thougth the screws were stripped. I would set the valve lash and drive about 100 miles (it was a daily driver) and have to reset the valve lash again. Finally the exhaust seat burned out. As the valve sank into the head, the stem would go slightly higher into the rocker, making the valve lash smaller which probably contributed to the burning. The final cure was to do the valve job and use the hardened seats for unleaded.
Ken thompson

This thread was discussed between 13/12/2001 and 17/12/2001

MG MGB Technical index

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