TO ALL WITH ENGINEERING BACK GROUNDS

[singapore stag]

Hi, I believe that the SOCTL have machined new aluminium cylinder Heads and are/have been tested.

I have two questions, please bear with me if i sound like a numpty.

Firstly.. Will these cylinder heads not suffer with the same maladies as the original ones?. The tiny complex water passages in the cylinder heads, will they not clog up again?.

My second question is... could not the cylinder headshave been made from another material other then Aluminium...and could the tiny water passages not have been made better so as not to clogthen the originalregardless of it being Ali/steel or other.

Sukh.

[DJT]

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Hi Sukh,

Have you read the information on the SOC Website? Log in from the homepage and look for the SOCTFL pages in the Members Area.

As for aluminium, there is nothing intrinsically wrong with this for cylinder heads, which is why almost every modern car on the market has heads made from alluminium.

My Brother-in-Law works as an engine designer for General Motors in Michigan. His speciality is head design. I asked him a couple of years ago to look at the spare Stag heads I had and give me his opinion. He couldn't comment about cooling waterways as he doesn't have x-ray vision but he did note the LM25 cast into each one. This refers to the grade of alloy and is one that is still commonly used for cylinder head manufacture.

As an aside. In many USA states there is a 5c or 10c payback on recycling of aluminium cans. The biggest buyer of these cansis Ford, and they go into cylinder head manufacture.

Cylinder head problems with the Stag engine almost all stem from poor maintenance during its lifespan. Not flushing the system, failure to use quality anti-freeze/corrosion inhibitor and failure to change the oil frequently. All these will lead to overheating. Follow these rules and there is no reason why the Stag cylinder heads won't last many years and 200,000+ miles.

Dave

[Barry Brown]

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With Aluminium heads there has always been a problem with casting which is not confined to the Stag, though during the late 70's and early eighties with the industrial problems it became more noticeable.
The problem is that if the metal does not enter the mould evenly then some of the cast will cool at a different rate to its neighbour. Since the metal is poured into multiple sprues then the multiple flows will meet but be at different temperatures and therefore density, causing a slight flaws in the casting.

On the 4 sets of heads I have had in my possession one set clearly had bad flow marks and was only fit for scrap, whilst on 2 other sets the more porous metal was ground out, refilled and machined, the last set had little signs of wear and required little restorative work.

I believe that getting a company to produce even castings was a major consideration for the SOCTF engineers working on the new heads.

Barry

[stag74red]

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Hi Sukh, I believe that alu is used because

1. Its has much better thermo conducting properties - therefore better combustion control, no hot spots etc.

2. Its lighter.

3. Higher Compression ratio, leaner mixture - better effeciency?

A clue to this is the Spark Plug Temp Rating -11/12, where as cast Iron heads use 4/5/6. If you put 5 's in a stag engine they would overheat, 11's in a Iron head would soot up.

Mark.

Please feel freecorrect me if this is wrong.

[al-stag]

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Sukh,

This is a question that I had too. I am an Engineer and I have many years experience in casting complex shapes in Aluminium. I asked this question on the forum before, but no-one seemed to know.

Iron casts much easier and better than aluminium. It flows better in the mould and iron head castings would probably have no defects at all. I think that the Stag's designers were concerned with weight. Cast Iron weighs almost exactly 3 times the weight of aluminium and you can imagine the considerable extra weight of cast iron and the uprating of front end components and brakes that would have to take place. The weight distribution would probably be wrong tooWith Iron the heat disipation would be somewhat worse, but on the other hand there would never be any distortion due to overheating as yourisk with the present heads.

Part of the problem is that LM25 actually begins to creep at about 150 degrees C. This is not too far above operating temperature. Under heavy compressive stresses around the bolts the metal will just ooze away relieving bolting pressure on the gasket and allowing leaks. So thats why even slight overheating spells disaster. Cooling has to be very good. Concorde suffered from this problem too, caused by kinetic heating (air friction) but it was solved by pumping the fuel around the airframe as a coolant to overcome it.

These days engine designers can use computer Finite Element techniques to accurately predict stresses and temperature gradients. This technology wasnt available in the 'slide rule' days, and thus you have an inherently poor guestimated design that was never really corrected through lack of ongoing development. EmployingFinite Element techniques on todays engines means that failures like those that occur on the Stag V8 are rare. I don't know what SOCTFL did, but if they just reproduced the old heads they have no doubt reproduced the inherent problem.

Al

[stag74red]

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Following on from Al,

This site has some info:

http://www.mrt-castings.co.uk/aluminium-alloy-lm25.html

quote:

Very prolonged heating, e.g. 10,000 hours, results in a sharp loss of strength at about 135 deg c.

MarK.

[Westfaling]

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Hi
I noticed in the link provided by Mark referring to LM25 that... "It is used in nuclear energy installations and for aircraft pump parts. LM25 may be superior for castings, particularly ingravity dies, which are difficult to make to the required standard of soundness."

We should remember that while Stag heads got a bad rep. effectively one of them at least was used in tens of thousands of other Triumphs and for many years by Saab in their 99 range. Saab rated their engine as very reliable.

[stustag]

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HI

If you read the SOCTFL report on these heads you will see that Mike Fisher and the team redesign some of the water ways to bring them up to today's standards with in the constraints of the original design (physical size and shape of the head).

They took a long time to find a casting company who could guarantee the quality of the process and end product.

Talking with Mike the heads have been run on a test vehicle without issues.

Stuart

[Stagspirit]

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Hello everybody



As I am the guy responsible for the SOCTFL Cylinder Head Project I have been prompted to respond to the questions raised by singapore stag. This is in fact my first post to the forum.



Aluminium Alloy grade LM 25 was the material used on the original heads, aluminium is the only option for replacement heads. When we started looking into the possibilities of remanufacture back in 2001 we sought expert opinion about the grade of aluminium and other aspects of manufacture. We sought opinion from Cosworth Racing because at that time the Managing Director, an acquaintance of mine, was a Stag owner. We were told that LM25 was still the most commonly used grade for Cylinder Heads and that whilst there are other grades which might offer a marginal improvement in respect of corrosion resistance they carry a significant cost premium and it would be difficult to find foundries prepared to cast them. We were also told that the heat treatment of the castings to the ‘TF’ condition is important in order to optimise the mechanical properties.



The size and configuration of the Stag Heads limits what can be done to volume and configuration of the water jacket. Gravity sand casting, the process used for low volume complex castings, determines the minimum wall thickness i.e. circa 4 to 5mm which can be cast safely and reliably. On modern cylinder heads in high volume production the wall thickness is slow as 3mm but they utilize much more expensive pattern equipment and advanced casing techniques which are not in our budget.



In any event SOCTFL does not have the resources or abilities to undertake and validate significant design changes even if possible changes were identified as being possible. SOCTFL can only support projects which replicate the original part or something very close to it.



All mixed metal engines i.e. a cast iron block with aluminium alloy cylinder heads suffer from corrosion over time. The problem with the Stag is made worse by the fact that 30/40 years ago British Leyland did not consider it necessary to tell their service network or customers that they should keep an inhibitor or high strength solution of antifreeze in the engine all year round. When plain water is used corrosion is accelerated, the water ways are further restricted on what is already a marginal cooling system, and overheating can occur. Distorted and corroded heads which require skimming and other remedial work was the result. Thus many head suffered advanced corrosion and skimming in the early days.



If Stag Cylinder Heads are in good condition built and assembled to the engine properly and maintained with an inhibitor all year round the engine will not overheat.

The new cylinder heads will be at least as good as the original ones and after all most of us are still running cars with cylinder heads which are over 30 years old. One of my cars has never had the heads taken off.



I hope this is of some help more will appear in the SOC magazine when we get around to writing an article about the project.



Mike Fisher - Project Director - SOCTFL

[al-stag]

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Welcome to the forum Mike, and thanks forsetting out SOCTFL's thinking

Al

[singapore stag]

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Hi Mike, Thanks for responding, I now have an understanding of what is and was involved in the production of these cars.

Yesyou are absolutely right that the original cylinder heads are still running our cars and that using the right antifreeze and inhibitors at the outset would have eliminated the corrosion and overheating problems.

Regards, Sukh.

[alan_thomas]

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Mike, Thanks for the informative post on the new heads. I would love to read more in the magazine as I am sure there were many hurdles on the way and I for one would be interested to know what they were and how the team overcome them.

One point I would like to know is if the aspect of siezed studs was considered by the obvious experts on the project. This problem is not due to the wrong type of coolant but due mainly to the galvanic reaction between dissimilar metals. Has any thought been applied to different head studs or coatings or increasing the hole dia to obviate this problem?

- Alan

[Mpower738]

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alan_thomas wrote:

Mike, Thanks for the informative post on the new heads. I would love to read more in the magazine as I am sure there were many hurdles on the way and I for one would be interested to know what they were and how the team overcome them.

One point I would like to know is if the aspect of siezed studs was considered by the obvious experts on the project. This problem is not due to the wrong type of coolant but due mainly to the galvanic reaction between dissimilar metals. Has any thought been applied to different head studs or coatings or increasing the hole dia to obviate this problem?

- Alan

In the marine industry Duralac compound is used on Aluminium masts to prevent pop rivets andstainless screws causing corrosion. I am planning to use it next time I remove the heads on my stag.

http://secure.silmid.com/ENG/product...50ML%20DTD369B

Personally I think increasing the hole size is asking for trouble, as there are no dowels to positively locate the head. If the holes are madelarger then there is more scope for the head to move about as it expands and contracts.

[mjheathcote]

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Duralac is also used on my Lotus Elise to prevent corrosion between mild steel brackets bolted to the aluminium chassis.

[Stagspirit]

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Alan

The problem with stud seizing was not considered by SOCFTL, it is not strictly within our terms of reference. Increasing the hole size would be design change which increases the risk of a break through into the water jacket soshould not be undertaken lightly.

However I will offer you my personal take on the matter. It is quite common practice to 'waist' cylinder head studs. This means to reduce the diameter of shank between the threaded portions. The weakest section of a stud is at the root diameter of thread. For a 7/16" UNC stud is 0.350" diameter. It is therefore quite safe to waist the studs to this diameter. In fact the original bolts used in the cylinder head were waisted to 0.375", so Leyland were not consistent in their approach to this issue 30+ years ago. This may not overcome the problem completely but is will sure go a long way towards it.

A further mitigation would beimproved plating, zinc offers very little protection. My preference would be nickel. Again not a total solution in its self but better, there are probably other surface treatments which will be prevent corrosion all together.

The use of anti seize compounds such as Duralec would also be of benefit. So if you use waisted, nickel plated studs assembled with Duralec you may well be able to remove your heads with ease in the future.


My next engine will be built with all bolts no studs waisted, re plated and probably assembled with anti seize but that is another story.


Mike