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MG MGB Technical - Questions on a new cylinder head

Greetings,

I don't post very often on the BBS, but I read it every day while I'm eating my lunch at work. Over the past years I've gleaned a lot of great info from this board. Thanks for that!

I developed a cracked head in my 73BGT and was unable to find a suitable replacement locally. So, I purchased the aluminum replacement head with valves installed and have a few questions.

1. Should I paint it?

2. Should I expect the installation will be problematic or non-eventful?

3. Are the torque specs the same?

4. Are there any special considerations I should be aware of while working with this head.

Any input would be appreciated. I would hate to spend that kind of money and blow-it by doing something stupid.

Cheers,
Dennis
Dennis Hosier

Hi Dennis
Years ago I had a HRG alloy head on a B and I kept all the paperwork that came with it. I've looked through it and there isn't any mention of a different cyl. head tension so I suspect it must be the same as a std. head. But having said that alloy heads are usually tensioned up and retensioned cold as the expansion of hot alloy gives you a false tension. Might pay to check with your head manufacturer for specs. Personally I wouldn't paint it unless it's a concourse car, I like the look of bare alloy it sort of looks like it means business.That's only my opinion though. Cheers Willy
WilliamRevit

Dennis. I have no experience with the aluminum cylinder heads. I have, however, read a lot about them when people have discussed them here. All of these discussions should be in the archives and would be worth reading.

I seem to remember something about aluminum having some heat transfer difference, as compared to the original cast iron cylinder head, which required the new aluminum cylinder heads to be less efficient as delivered. Something about the cylinder heads needed to be milled before installing to raise the compression ratio which needed to be higher with an aluminum cylinder head than with a cast iron cylinder head.

One area which I am familiar with is the corrosion problem with aluminum parts--a local mechanic friend brings me parts off of customer cars to bead blast for him. Quite significant amounts of corrosion during relatively short operations life (less than ten years of operations service life). Anti-freeze seems to be a factor in this. Might be worth while in making sure that any anti-freeze you install is designed for use with aluminum engines/cast iron and aluminum engines. My mechanic friend has eight different modern anti-freeze mixtures on hand depending on which make of car is being serviced. Hence, an area which I have not seen discussed and one worth researching.

Les
Les Bengtson

Hi Dennis,

You are moving into an area I have considered on my 1966 MGB, installing a Moss aluminum head. The questions you pose are quite interesting. I too have concerns about such a change. What sticks in my mind the most is that aluminum has a coefficient of linear expansion about two times that of iron per degree centegrade. Given that, it would seem to me that there would be uneven movement between the head and block, as well as different heat transfer over time.

Any info or thoughts on this?

Jim
Jim Hanks

In my experience with alloy heads the head gasket is of optimim importance. All modern alloy head/iron block engines use a three peice gasket to allow the movement of the head in relationship to the block as the coefficients of expansion are quite different. RAY
RAY

Hi folks,

All answers in P.Burgess's book "How to power tune B series engine". It's necessary to either shave off the alloy head or swapp dished pistons to flat topped ones. There's a job to achieve onto head ports to improve flows, but great advantages: much better heat Xfers, Already unleaded compatible, cross flow configuration available too...,for yet more output.
RG.
RG.
Renou

Certainly for performance the alloy heads need the rework discussed above. Also check out Sean Brown's site at www.flowspeed.com.

My question is do you need to do shaving and porting to stay at the stock performance level or near it?
Robert McCoy

I've had the alloy head on my 74B for about 5 years now. It was not a performance build but just a standard engine for unleaded gas. If I remember right, I used the hardened studs from ARM and the gasket had copper on one side. I used spray copper all over both sides of the gasket. After torqueing it, I ran the engine to warm it up and let it set overnight. Then the next day I re-torqued it again. After that I just started driving it and haven't had any problems. It's got probably 30,000 miles.
When I had it all apart to put the new head on I had the radiator checked and it never overheats. I have a mechanical temp gauge and last summer we had a few days over 95 where it ran up around 200 (with a 190 thermostat) and it never vapor locked or ran bad because of heat. That was when I pushing it to 70 and 75 mph on the highway. If I keep it down around 60 to 65 then it stays where the thermostat is. When it's below about 60 degrees out, the temp stays about 160 even with the 190 thermostat.
Overall I'm very happy with the alloy head and don't recall any problems at all.
thanks,
Ken
1974 MGB
1973 MGB parts car
1990 Miata
Kenneth Thompson

Not sure what the current heads are like, I have one of the Pierce heads from about 12 years ago. The ports were a bit rough, but not really bad. As to compression ratio it depends on the chamber volume. On mine with a .060 overbore I had to open the chambers up to keep the ratio below 11to1. Peter Burgess's book has the formula for this. I would suspect that leaving everything stock will keep you within the limits of todays gas. As a general rule an alloy head will allow 1 point more compression ratio above an iron head.
Ron Smith

Dennis-
Clough & Wood in the UK made the Original Equipment cylinder head gasket on the early cars. They were asbestos faced with copper on one side, and either steel or copper that was colored in order to look like steel on its other side. While technically obsolete, they work very well with cast iron heads if correctly installed and retorqued after initial running-in. The Roadster Factory sells them here in the USA.

While today’s sealants are excellent and today’s modern cylinder head gaskets possess greater compressibility than those of the past, they can compensate for warped mating surfaces only to a very limited degree. Instead, use either a Payen or a Fel-Pro cylinder head gasket or one that is marked FRONT/TOP, as these should be quality gaskets. These gaskets are resin-impregnated, have copper sealing rings to better resist excessive crush pressures, and require no additional sealing coatings. The resin softens when it gets hot and makes a better seal. These gaskets seal by heat-bonding to the mating surfaces of the cylinder head and the engine block. If the mating surfaces are not scrupulously clean, or if you allow the coolant to pressurize before the bonding has fully taken place, then the resin-impregnated gasket will not bond properly to the mating surfaces and subsequent leaks will be more likely. They are particularly appropriate for use on engines that have been converted to aluminum alloy heads as they handle the differing coefficients of expansion of a cast iron engine block and an aluminum alloy cylinder head quite well.

Because of these differing coefficients of expansion, a copper cylinder head gasket should never be used in combination with a cast iron engine block and an aluminum alloy cylinder head. Racers like copper cylinder head gaskets for two reasons: First, because they have high crush resistance, thus permitting the application of higher levels of torque onto the cylinder head stud nuts in order to deal with higher pressure levels of both compression and combustion. Second, because they frequently tear down their engines for inspection. This being the case, they do not want to have to spend time scraping bits of torn fiber gasket from the mating surfaces. Beyond those two advantages, copper cylinder head gaskets are obsolete. Certainly the break-in procedure for them can be challenging. Many of these copper gaskets have the letters “DV” stamped onto them which stands for “Double Varnish”. These varnished gaskets require that run the engine be run without coolant until the cylinder head becomes hot enough for the varnish to soften and form a seal, then left to cool down for several hours, or, ideally, overnight. Of course, the trick is to reach the appropriate temperature without exceeding it and risking damage to the valve seats or the seizure of a piston.

Never allow a cylinder head gasket to overhang into the bore of the cylinder, as this will lead to a blown cylinder head gasket and / or internal damage to the engine. The Fel-Pro and Payen cylinder head gaskets have a slightly larger bore diameter than that of the Original Equipment cylinder head gaskets do, thus permitting displacement to be increased to as much as 1925cc without the risk of overhanging the bore of the cylinder. They also do not cost an arm and a leg as the Competition cylinder head gaskets do. If you have chosen to build an engine that has a bore diameter that is larger than that, then you will need to install a specialized Big Bore cylinder head gasket. Cambridge Motorsport offers a Competition cylinder head gasket for bore sizes of up to 84.4mm (83.5mm=1950cc). Its triple layer steel shim construction offers reliability even with the highest compression levels. This gasket is, to my knowledge, the only reliable solution for Big Bore competition engines, and can be reused up to three times. Cambridge Motorsports has a website at http://www.cambridgemotorsport.com/ .

You will need to retorque the cylinder head immediately after the initial running of the engine. Note that, as Les correctly pointed out, a cast iron cylinder head should be retorqued while the engine is hot, while an aluminum alloy cylinder head should be retorqued when it is cold.
Steve S.

Thank you all for your time and insight. Ken, I'm just looking for a replacement as well, thanks. Steve, I have purchased the Fel-PRO kit, thank-you. Les, I've sent an email to Pierce as well. I'll let you all know what comes back from them. Dennis
Dennis Hosier

Just use standard torque specs.

I would suggest you get the head surfaced because they are NEVER flat from the box. That does not mean they won't seal right out of the box, but I like to be sure there will not be any problems. There is nothing more discouraging to find than coolant leaking out right after you got done installing the head.

The studs needed on the manifold face are course thread rather than the original fine thread, so you'll have to buy some new studs as well.

Performance is about like a stock head.

I would not go and try to increase the compression ratio radically at this point. If your engine still has the stock low-compression pistons in it, you're wasting your time until you get some higher compression pistons to start. At that point you'd be doing a full rebuild and could easily plan the build accordingly.


Sean
Sean Brown

Dennis: I have an alloy head on my 1979 MGB since 2004 and pleased to report no problems. The head was milled to assure its eveness prior to installation. Even when I had the car overheat this summer due to a failed thermo-switch in the radiator. It's been approx 9k miles since the rebuild.

Jim: Volvo has been using alloy heads on cast iron blocks sint the advent of the B21-F 4 OHC engine and has not had a problem. Ray's comment about the head gasket material and construction of the gasket I would agree is of utmost importance due to the dissimilar metals as well as the mass of the two major components.

Again, I concur with the others who have posted their success with the alloy head conversion. So I would feel confident advising you to do the alloy head change.

Be sure to have the head milled to be sure of its eveness and get the proper head gasket kit.

cheers

Gary :>{D
79 mgb
gnhansen

I did hear back from Pierce and they said:

Torque it cold and to original specs.

It is a direct replacement for the original, (I had mine checked at a shop and it was true as well.)

No special antifreeze is required.

Painting is not required, if you wish to do so, it won't prohibit functionality.

They do not come with a three-angle valve job. I had one done on mine at a local shop for $70.

I told them I had purchased the Fel-PRO gasket kit and they said that would be fine.

Between this information and the posts on this board, I'm looking forward to this replacement.

Cheers,
Dennis
Dennis Hosier

Regarding the CR, I would think ally heads run colder (better heat transfer), and that would mean they could take more CR before detonation. And more CR means more power!
Neil
Neil

This thread was discussed between 30/09/2008 and 10/10/2008

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