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MG MGB Technical - mgb cylinder head

After a few problems with the running of my 1976 engine,== (poor running and small bubbles of froth in the rad water) I decided to remove the head. Would it be wise to get my local motor factors to do the necessary work to convert it to run on unleaded. What does this entail and should i have it skimmed?? thanks in advance. Trev Walton
trev walton

Trev. You are going to have to remove the head, have it inspected, replace any worn valve guides, replace any bad valves, and have the head skimmed if it is not flat. You will, most probably, want to have a three angle valve job done while the head is off. Installing hardened valve seats--an "unleadened conversion" will be a relatively small portion of the overall cost. Just doing a valve job will remove the lead deposits on the rim of the valves and the seats, requiring the use of a lead based additive to prevent damage. Considering all of the other work which needs to be done when a cylinder head is removed and rebuilt, the fact that unleaded fuel has become the defacto standard in the Western world, and the work to be done would require the expense of a lead additive, if available, at every fill up, I tend to have my cylinder heads converted. What you do is up to you.

Les Bengtson


It depends...

Assuming that the froth is a head gasket problem then it may be fine if you just put it back on. That's the cheapest solution.

You'll only need it skimmed if it is not flat, so you'll need to check with a straight edge (a proper ground one, not a cheap spirit level). If it's flat, and everything else looks okay, then put it back on!

You're going to want to take the valves out if you get it skimmed, so you may as well do a proper job. If you do all the work that Les says, then you're going to be better off buying a head already done (it's £40 for a head skim around here), and you can see the price of valves, springs etc in the Moss book.


Conversion to unleaded is more work, more cost, and more work is likely to cause more problems. It won't give you any more performance or allow you to run a lower octane fuel, it only affects whether the valve seats may recess or not. And an engine that has run at least 40k on leaded, and hasn't had the valves replaced or seats recut, is very unlikely to experience recession in the rest of its natural life unless you use it at full throttle for long distances. Use a lead-replacement additive if you want extra protection, but the USA has been unleaded a lot longer than the UK, I suggest fewer people have had the head converted than not, and I have never heard of a case of recession in an MGB on either side of the Atlantic.
Paul Hunt 2

If you are having the head completely rebuilt then you may as well spend the extra and have the unleaded job done on it (I doubt you can buy one off the shelf without) just in case it is better, But I wouldn't do it just because the head is off...


By the time you get all that work done, you'd be better off buying a head already done from Peter Burgess. Talk about money well spent!!

You won't regret that!

Paul K

I would second the idea that you shouldn't worry about it unless you're racing. The ultimate endurance test has already been run here: Catalytic converters became standard way back in 1976. Leaded fuel was uncommon by the early 90s and was banned outright in 1996. Plenty of old cars have run for a decade or two with no conversions, no additives and no problems. Sustained full-throttle operation may be another story.

If you're already having the valve seats done, you may as well convert, but do it on a why-not basis, not on a must-do basis.
Sam Good

Anyone know of the top of their head how much it costs to buy one of those Burgess heads and ship it to the US? Or is there a good alternative already sold in the US? I may be in the market for a head in the near future.

Peter Burgess advertises on this website and you can check specifications and prices there. Here in the US, the Seven Shop, operated by Mike and Sean Brown do modifications to MGB cylinder heads.

Les Bengtson

I have had two MGB's where the rear most valve recesses. On both MG's it was the same valve. This may likely be due to the higher highway speeds of today (75-85mph). The simple stalling strategy is to adjust the valves every 1500 mi instead of every 6000mi. Eventually there will be no more adjustment left.

Any local automotive supply store can recommend or has a shop for you that will do a good job of rebuilding the MGB head. this will be cheaper than the two specialty shops below but at no increase in performance.

The two shops I know of in the US for getting increased performance (ported heads) are:

The Flowspeed site has most of the answers for your questions. I have not personally used these shops.
werner haussmann

"the rear most valve recesses. On both MG's it was the same valve"

That sounds like other problems to me, like too weak a mixture causing higher temps?
Paul Hunt 2

Peter Burgees has written a book about how to powertune the MGB. With the information given there, every one that is able to do a porting job on carst iron cylinder heads will be able to do all that kind of modifications everywhere.

May be it is a good idea to invest into this paperback and take a decission after reading all the hints given there.

If someone is able to do the porting himself, be sure it works and the machine shop will only have to install new valve guides, may be seats too and cut the valve seats according to the data given.
I can only tell you that the investment in thes book payed for itself and the result was outstanding.


One crucial bit of advice about Do-It-Yourself heads: Be Careful! Once you remove metal, you cannot put it back. To use a Dremel tool with a flap sander attachment to smooth the existing contours is one thing, but to alter the contours with a grinding stone or a rotary file is something else. Peter Burgess gives some crude drawings and simple instructions in his book “How to Power Tune MGB 4-Cylinder Engines” and says that you can do it yourself, but a highly practiced Master of the art often forgets how hard it is for a rank beginner. He gives a much fuller and more detailed description of what is actually involved in his later book “How To Build, Modify, & Power Tune Cylinder Heads” which should be read prior to deciding to set out on such a venture. Remember, the B Series cylinder head is special. Siamesed ports are an antiquity in this modern era of crossflow heads with separate ports, and there are very few people who truly understand the subtleties of them. This is no Ford or Chevrolet V8 cylinder head we are talking about here! Serious work on these heads entails specialized knowledge and skills. Just the process of removing the valve guide bosses is very tricky due to the fact that the difference between removing just enough metal and breaking into one of the cooling passages is very, very small. If you do not have genuine blueprints of the ports in the particular cylinder head casting that you are working on (there were four that were used on the North American Market engines alone), complete with dimensions, radiuses, etc., and the appropriate precision measuring tools, then you are taking a big gamble with all of the odds stacked heavily against you. You will need a Flowbench, too. This machine equipped with sensing probes draws room temperature air in through the intake ports and blows combustion temperature air out through the exhaust ports. It is a must-have for getting the air flow rates of the ports individually matched at all points of valve lift at all engine speeds within the engine’s operating range. If the airflow rates for each cylinder are not equal under all circumstances, the result will be differing fueling requirements. This is a serious problem for an engine in which two cylinders must share the same metering device. In addition, with differing quantities of air entering into each cylinder, the Effective Compression Ratio will also correspondingly differ, making for rough running.

Many well-intentioned local Good ‘Ol Boy Hot Rod Motor Builders (the ones that the local pimply Hot Rodders call “experts”) have reduced MGB heads to scrap metal. Once this happens you will spend at least as much money buying another cylinder head and getting the parts for it as you would have spent shipping the cylinder head to a qualified professional, having him do the work, and then shipping it back again, complete with insurance. The one thing that you cannot cheapo your way through on an engine is the headwork. Without access to a flowbench, blueprints, measuring instruments, a good working knowledge of the mysteries of siamesed ports, and the specialized skills, the likelihood of an amateur doing it correctly on a first attempt is so small that it makes me shudder. How do I know? About twenty-six years ago I worked for Rockwell International making valves for use in nuclear power plants. The valves had to be flowed on a bench to be government certified for use in a nuclear installation. This meant custom contouring work, all done by hand with a die-grinder-type Dremel tool. It took about three years of prior experience and a practiced eye to be able to do it right every time, and this was working daily for eight to ten hours with a flow bench, repeatedly making small corrections on every individual port! Recontour siamesed ports on my garage workbench? Hey, my name is not Peter Burgess! Ship the cylinder head to Peter or purchase one from him outright, you will be glad you did. After all, you would not try to bore your cylinders in the garage with a file, would you?
Steve S.

Come on folks-Give it up for Bigface, once again showing that correctly chosen, many words provide insight, when fewer could not do. A pleasure, Steve! Cheers, Vic
vem myers


for reproducing equal prepared heads in a commercial buiseness, a flow bank is a must. The valves you are refering about can be compared too to this situation.
If someone has no idea about flow, the chance to ruin a head is evident and without any practical experiance on preparing heads, a lot of investigation is also a necessary must.
When i prepared the first head (not an MGB one) 35 years ago, the result was poor but helpfull.
Having been involved in aerodynamical and hydronautican develpments for several years, i learned a lot about flow and also learned what helps and what should be avoided.
Peter's book contains all the information necessary to reach a good result if someone is able and knows how to use the right tools at the right place.
Within the last few years i prepared two 'ralley' heads for my cars and the result was within 1BHP on the rolling road on the same engine block.
The engine is a 1868ccm with Piper 285/2, county flat top pistons, HIF 6 carbs and the RWHP readings were 99.7 and 98.6.
The difference might be explained due to seasonal temperature differences while the test runs were made.
So everyone who is willing and able to port a head of a B-Series engine should end up with reasonable results when using the advice given by Peter, although you will also learn to understand why porting the B-Series head is that expensive.


Just an another 2cents worth...

This summer I had a valve job on my 72B, with at least 88,000+ miles on a car with a broken trip meter.

Compression test suggested the need, as did tell tale smoke on start up - indicating valve guides/seals.

Even the shop was surprised to see how far the exhaust valves had sunken into the seats, or what was left of them.

I replaced all exhaust with hardened to enable unleaded use. The added cost was minimal.
R.W Anderson


I listed two shops in the US above. Do you do MGB ported heads? If so let's have a web page or address. A complete list would be useful for future reference.

I plan to do one in a few months, but at this point I am very unsure of where to go. Are there any other reputeable shops for ported MGB heads?
werner haussmann

If I remember correctly, it cost just about $1K for an Econotune head fully assembled, along with a stock grind (Peter's recommendation) cam from Piper, plus freight from the UK. In addition I spent $128 to mail the head to Peter after having it magged and PTed. If you look at the price list on Peter's web site, roughly double that number for the conversion from
Paul K


Have a mail at Sean Brown. He realizes the same job as P.Burgess on your side.

No, I don't modify MGB heads on a commercial basis because I don't have a flowbench. Your list is the same as mine. If someone wants to do his own head at home in the garage, there are a few things that I can recommend-

1) Match the volumes of the combustion chambers.
2) Match the throat of the port to the seat very carefully after the unleaded seats have been installed.
3) Install tapered (bulleted) valve guides.
4) Have the shop do a three-angle grind on both the seats and the valves.
5) Use a Dremel tool with a flap sander to remove any casting lumps and bumps and smooth out the walls of the ports. Machinist's bluing on a straightedge should be repeatedly used to check the straightness of the walls.

This will give the rough result of an "Econotune" head. Note my use of the word "rough". Anything beyond this requires the services of a professional tuner such as Peter Burgess.
Steve S.

I have that power tune book and it is a very interesting read although like others pointed out some of the things described in there are beyond the scope of an amateur! Worth having though for sure:

I basically did almost exactly what Steve S suggests above. I found that was well within my capabilities and actually fun to do. Matching the chamber port volumes wasn't too hard and generally smoothing off the head with the Dremel was pretty easy. A normal head does seem to have a lot of burrs on it. I didn't attempt anything radical, just generally smoothed things off.

The slightly annoying thing was I had to do it all twice! My first head ended up having a crack in it. I definitely recommend having any used head crack tested BEFORE you go doing a lot of work on it.

Despite having the seats converted to unleaded I will still use additive in the car. It won't be a high use car so the extra cost doesn't worry me. I don't think it hurts using the additives (Castrol Valvemaster) when technically you don't really need to?


Simon Jansen

This thread was discussed between 18/10/2007 and 29/10/2007

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