I believe my statements are considered and correct.

Studs do pull out of Magnesium cases - simple fact.

The impact of heat on the magnesium and the thermal damage it has accumulated is typically unknown. The combined influence of preload and time at temperature and the resulting Stress Relaxation is unpredictable and quite possibly varies with the minor change in alloy content on a batch by batch basis.

It is not just the threads that are damaged by heat but the body of the material subjected to load and heat. The extent of any damage is difficult to determine so a conservative approach seems sensible.

Ensuring that a mag case can be used successfully is a matter of risk management.

Henry, I have never said "if you don't use Dilivar the increased loading will exceed the mag case ability to hold the stud securely". This is your statement.

I have said that I believe it is wise to manage the increase in pull out force to minimise the long term risk to the engine case and that Dilavar will produce the lowest stress and this statement is correct.

Why take the risk.

A stud with a larger than standard shank diameter will significantly add preload to the the threads and must, therefore increase the risk of long term damage.

This type stud has not been designed to minimise the impact of increasing preload so does need case savers and thermal management may compensate but again why take the risk?

We have argued before about using thermally induced forces to control the integrity of a clamped joint.

I have stated quite clearly that I believe that this strategy is unwise. If a cylinder head joint is not correctly clamped when the engine is cold then damage will start to accumulate and the amount of damage will be proportional to the number of thermal cycles.

I am of the opinion that Heads need to be correctly clamped at all times and I find it difficult to understand why you don't agree with this concept.


This is, indeed an interesting statement and is a debate that we have also had before.

Early Dilavar studs obviously fail on a regular basis, this is indisputable.

The material selection was clearly flawed and I made comments about potential reasons in the past and I don't think they need repeating but the current coating technique should eliminate most of the issues.

Standard steel studs very rarely fail and have been produced in significant numbers.

I am quite sure that Supertec studs won’t fail this is not the subject that we are debating.

I don’t really see why Dilavar and ARP studs should fail to clamp heads if they are correctly tightened.

The basic thread quality of a Dilavar stud is excellent and better than most aftermarket studs in terms of ‘fit’.

ARP studs seen to be made to a commercial fit but surface finish of the thread is excellent.

I hope that one day the price of Ultrasonic preload measuring systems become low enough to be affordable and then we will be able to learn more.

Obtaining consistent preload with simple torque tightening methods can be difficult and is why we are looking at alternative strategies.

If you take 6 studs, 6 nuts, 3 torque wrenches and 3 people and measure the variation in preload resulting from each individual tightening a stud 3 times than the most significant variable is the individual.

There is a very useful statistical technique used in this analysis and 'operator sensitivity' is always a significant feature in any manual technique and is the main driver behind computer controlled testing.

We are all convinced that we always tighten fasteners correctly and consistently but sadly this is very unlikley.

I think it is time for me to bow out of the Head Stud debate. The basic facts should be clear.

The distribution of load is a very simple to determine and the risks are obvious, there is not much more to be said.

I am surprised you can’t achieve 1% in a static application. Having manufactured precision load cells in my previous business that were used in force calibration machines all over the world and 1% is not so difficult.

I agree about dynamic noise but digital filtering is now relatively straightforward and we are only interested in the thermally induced forces so I am confident that we will be able to discriminate. I am sure ‘time constants’ will indeed be long.

I have worked with Force measurement systems for around 40 years and so I am reasonably confident that we can obtain meaningful data.

To digress my company manufactured a Torque transducer installed in a V10 FI engine back in 2004 and effectively measured Horsepower in real time and transmitted the data using telemetry back to the pits.

We achieved a torque measuring accuracy of around 0.5% without too much difficulty and the same transducer provided a speed output as well as a phasing signal to evaluate torsional vibration. This development was subject to a NDA and hence could not be publicised.

We had a similar system installed in the Ford Focus World Rally Car and this provided data to the traction control system.

We also manufactured Torque transducers installed on Industrial Turbo compressors (Up to 100MW) and achieved 1% accuracy on a routine basis.

Studs do pull out of mag cases. We know the why. But when? I think 40-42 years is plenty long enough for reasonable service with steel studs. I see no reason why one shouldn't expect 40 more at close to stock power levels and no thermal reactors.

Of course the last benefit is a substantially lower price.

Henry,

My final word on this topic at this time and I am sure you will disagree.

Supertec studs will increase the pull out forces due to expansion due to their increased diameter - the case may survive this increase but it is not due to stud design as your choice of stud diameter is the cause of this potential problem.

If your studs do ever pull out of a mag case what will you do?

If a case saver has been installed and they still pull out it is all over and prudent design should do everything possible to avoid this catastrophic outcome.

It may be unlikely but again why take the risk for what seems like a very minimal benefit.

Would I fit a case saver and a Supertec or any other aftermarket stud to my matching number 2.7 M471 engine - never in a Million Years - so the decision becomes more and more clear as the value of early original cars continues to increase.

I cannot understand why you believe your stud is easier to install than other studs that are available and I don't agree with this statement.

You keep stating that your studs improve cylinder head stability but the preload when cold is no different to any other stud for a given torque something you clearly don't accept.

Your hypothesis that increasing preload due to expansion is in my view flawed and not correct.

The extra length of the thread which is screwed into the case has little of no practical significance.

And I just simply don't see how you gain better clearance for Twin Plugs.

Your studs are clearly MUCH more expensive than a standard steel stud, they have an identical coefficient of expansion and reduce the increase in the pull out force on the thread by more than 50% compared to a stud with a larger shank diameter.

If the case saver and heat management allow a mag case to survive with a Supertec Stud then they will survive equally well if not better with a standard steel stud and even more money will be saved.

Standard steel studs also have a very good record with regard to breakage, have really stood the test of time and have the best class of fit of any 911 stud I have ever measured.

I will always believe that the increased diameter of any stud used in this application is a design flaw with regard to magnesium engines and I have I believe, made a valid case that this is a simple fact.

It is obviously up to individual customers to decide what they should do with their engines and as you say we will always disagree.

I am in the process of making a very small quantity of 17-4PH studs (Only 5 studs) with rolled threads and an increased shank diameter.

We have the material the blanks they are ground and will be thread rolled next week.

We will then add the strain gauges and run one set on our test engine.

We will run another cylinder with standard studs, one cylinder with a set of early Dilavar studs and one cylinder with Titanium studs once we have collated all the data with regard to force versus expansion we will publish the results to any interested party.

I don't know about you gents, but this is what I call a thread 😜
I am about to rebuild my mag 2.7, and I do not want to take any risks as I currently have a pulled stud at #6. It is my belief, and correct me if I'm wrong Henry, but there is no proper top end rebuild due to the mag warping once you take the cylinders off the case, as the spigot deck must be absolutely flat. I don't mind buying studs made from Mars material if it ensures me no pulled studs.
Chris, I appreciate your recent emails, as with you Henry. The fact both of you are genuinely interested in plebs like me and my build speaks volumes.
Don't let the debate get nasty.
Henry, how long have you been selling these studs and what would you do if some started pulling?
Has anyone experienced pulled studs from a mag case that were either steel or supertec (or other) whilst employing case savers/oil cooler etc?
Chris, I still don't understand why you prefer a timesert over case saver???
Cheers
Dan

I would never deliberately offend Henry although I am sure that he strongly disagrees with me which is absolutely OK.

In both Academic and Advanced Engineering teams it is quite normal to have strong disagreements and to argue and to be challenged is good for us.

I recently wasted time and money making a PTFE Seal - it worked but was costly an could have been a failure.

Henry, wisely suggested that we should shorten the garter spring which is, of course a much better idea. Sadly something I had not considered (Doh!) and I really appreciated the input.

With regard to your question I think Timeserts give you a second go - case savers seem to be the final chance.

I have never had issues with Timeserts but many others that have built more engines that we have seem to suggest they have had problems.

I have several colleagues in the UK who have been building 911 race engines for many, many years and always use Timeserts and I tend to take a lead from these guys.

I would admit that it is easy to believe them as I already want to use the timesert :)

I would also say that all of these guys also tend to use Dilavar studs with mag engines so perhaps the reduced load helps.

I don't really have that strong view and would accept that the case saver is a stronger solution.

I first used Timeserts on my first 911 in 1986 and never moved away from this solution.

We have always used a vertical mill to prepare the cases and to ensure that we everything squared up.

The problem with die cast magnesium is that it tends to suffer from the effects of creep at temperatures around 120 degC.

The impact of the stress developed in the thread has a measurable impact on the behaviour of the magnesium alloy and there is enough information it this link to explain the issues that are involved but it is quite heavy going.

http://i197.photobucket.com/albums/a...psnnhnayk3.jpg

This simple graph shows the influence of stress on AS41 Die Cast Magnesium’s sensitivity to damage accumulation with increasing stress which is shown as strain on the Y axis

The temperature this data was obtained at is 150 degC and I would agree with Henry that good temperature control is extremely important as this also has a significant impact on this relationship.

The structure would almost certainly be more damaged tolerant at 125 degC the question is how much more tolerant.

I believe that AS41 starts to cause some problems at around 125degC but there isn’t too much published data hence my conservatism.

Some of the magnesium alloys are better than this but their process history, grain size and alloy content even within the range permitted all have an influence.

The difference between a good result and a damaged engine when long term behaviour is considered can be as small as 10 to 15 degrees if stress levels rise too much.

https://tubdok.tub.tuhh.de/bitstream/11420/824/1/Anopuo_genehmigte_version.pdf

Hi Dan
At the point where head studs /or one is pulling it's time to split the case.
The reasoning is that case inserts should be installed using my mill to insure that the studs are installed straight. You can't believe the hassle you'll encounter if the studs are porcupined.
After we install CaseSavers we like to true the spigot bore and deck the cylinders.
We recently decked a case that had a .030" difference between spigots.
We have been selling our head stud kit since 2004. We tested them in race engine and our own cars for about five years before that. We've been using CaseSaver on mag case engines for close to 30 years (250+ engines).
In the US, 2.7 engines came from the factory with smog equipment that produced high (245-260 and more) engine temps which reeked havoc on the case.
The damaged created by all that heat made the use of those cases limited to very mild builds but to answer your question, I don't remember a single engine we built in the 15 years that suffered from stud pull off.

Chris, is this your final, final word on the subject or just your next to last final, final word on it? LOL lighten up dude, life is way to short.
Thank you for your persistence. I appreciate the opportunity to explain my studs to the building community.

"What if" is always a cool scenario but sometimes just seems silly. What if my plain yogurt came with a strawberry in it? I would survive but it's never happened.
edit (My nephew just read this and questioned "but what if it's a blueberry?" and my response was "yuck, I might die!" knowing how much I hate blueberries).lol
What if the CaseSaver pulls out? CaseSavers come in many different sizes. We install the size required to perform the job properly. That feature allows us to repair case that had Timeserts mistakenly installed.
edit: BTW, we have repaired many (not one or two but many) a mag case that had Timeserts and Dilivar studs pulling out. Imagine the horror if one of these butchered cases was an RS or even 906

Wow!! "Not in a million years" ......I generally build what the customer wants and will bow to the customers desires even if that means using the head stud (or whatever) of their choice. I give my best advise, just like I do here and build what the customer wants. As you can see in the picture, the rod we used was a Pauter rod. They are of incredible quality but not my favorite design and yet the customer preferred it so we used it.
There are many Million dollar+ 906, RS, RSR and 935 engines in the US and the rest of the world built with Supertec head studs.

Ease of installation is a huge issue for us. Since stud install height is no longer an issue, we can install the pistons and cylinder package before we install the studs. You will never understand the shear joy this simple change will make in building a 911 engine.

http://forums.pelicanparts.com/uploa...1475846793.jpg

Twin plug clearance is a reference to the interference caused by the standard allen nut used by Porsche. The lower left hand allen nut must be replaced or modified on a twin plug conversion to clear the spark plug connector. . Small issue but another plus for Supertec stud kit.
edit: For those who don't know, the Supertec kit comes with studs, ground, hardened washers and 12 point, serrated flange nuts.

The extra length of the stud allows for special build applications as well as more thread engagement in a none inserted case.

If I missed anything I'll try to address the issue later. Right now I'm off to the shop.
Cheers

Henry, I just enjoy the argument and sadly have no other life :D

I have studied and enjoyed Metallurgy and Materials since I was 16 years old and it is just a significant part of what I have always done.

One final, final, final comment.

Would I fit a case saver and a Supertec or any other aftermarket stud to my matching number 2.7 M471 engine - never in a Million Years was in fact the comment I made. ;)

Sorry about the mis-quote......

And yet Chris, all three engines you bought from me had Supertec head studs. Do you have some stud related stories/complaints to relate about those engines?
Didn't one on those engines win a vintage rally championship?

http://forums.pelicanparts.com/uploa...1475851976.jpg

The engine that we used in the Championship winning car was a great engine .

The other two blew up when the studs failed - SmileWavy

Of course I am not being serious - They also performed extremely well and everyone was very happy with their performance but sadly the other cars were not driven as well and didn't achieve any significant results.

Great engines, great price and a good job.

We sent several other people your way and everyone has been happy.

On an Engine with Aluminium cases I have no doubts about your head studs and have said so on many occasions.

I have absolutely no issue with any aspects of your engines and the great value for money you provided us.

Your quote was the most comprehensive we received, the detail was great and the engines did exactly as promised. You made the three other companies that we approached for quotations look amateurish. I still have a copy of your original quotation in one of my files and have used it as a model for making offers to our customers. It has been very useful.

I just disagree about the basic concept of using a stud with an increased stiffness on a mag engine and over the years we have disagreed about some minor details and in some respects we do things a different way BUT since we started our own business we continually strive to live up the high standards that you and others with more experience have set and will continue to do so.

We have developed a little more expertise over the last 11 years and I believe we have improved in many areas.

We do also have some very detailed and I believe accomplished engineering design skills. Two of the guys are Graduate Mechanical Engineers and I specialised in Engineering Materials Behaviour and test system manufacture for more than 30 years.

We are not simply theoreticians we translated our knowledge and ability into manufactured product every day. We were suppliers to the majority of F1 teams, NASA, Rolls Royce, GE, Honeywell, Lockheed Martin, Boeing, Bell Helicopters and the majority of Blue chip engineering companies around the world.

Unhappily we still do screw up from time but we always stand by our mistakes.

We now make flywheels, we have made 2.0 litre 906 style cranks and rods and we are we are considering making cylinders.

We are currently developing pistons with a new supplier in Birmingham.

There is a small company that has a piston forge and a piston lathe and they have been making a very wide range of Ford Competition pistons for the last 12 years but they sell them all to a company that uses their own private brand name and they are practically invisible.

Our crank manufacturer also manufacture exclusively for the trade and has no brand. They are based in my home town and have been making cranks for more than 100 years.

They used to manufacture all of the Cosworth DFV crankshafts but are now a relatively small company and very specialised.

I have bought cranks from them (not Porsche) for 30 years and they are very good.

We have made vernier adjustable cam sprockets which we have in around 30 engines.

We have now delivered around 600 forged adjustable rockers and the die for the 906 rocker has just been sunk.

We have our own Plate Type LSDs and 915 gear sets.

We will make RSR style Aluminium sprockets next month.

We have straight cut gears for the intermediate shafts.

We have designed but not made a range of 300M Drive flanges for 901. 911 and 915 transmissions,

We have all of the parts to completely overhaul Nadella Driveshafts including re-manufactured seals and the first Solex 40PI Intake manifold castings arrived today.

We have our own Weld-in Rollcages which have been approved by the MSA in the UK and make early style 911R roll cages with the correct centreline radius,, correct tube sizxe and the early cast steel crow's feet to weld into the bodyshell.

We also make a range of glassfibre panels, steel repair panels for body shells, wiring looms, RSR Strengthening panels and we are just testing out new coated stainless steel diaphragms of CIS fuel distributors. We have gathered up around 20 fuel distributors and have completed a small calibration rig to set them up correctly

We make our own rubber press tools and have a small Dual Form to manufacture small pressings.

The new Dansk Floor Pans are an example. You can only buy a LHD floor.

We make the additional pressings that Porsche used for mounting a RHD Pedal Box and they sell very strongly. This change needs five small pressings and we make them all.

Our CAD Drawing register now has 245 designs and with the parts that are not drawn we have around 300 parts that we manufacture.

We do try to keep busy :) but we make most of our parts to service our own needs and are not too good at selling them on.

Wow Chris, thanks for the kind words.
It really looks like you have some very cool projects on the board.
Best of luck with all of them.
Cheers
Henry

Legends 😎

Chris/Henry....great information so one can choose an educated and informed route.
I appreciate both the work and discovery you guys partake in and the free education that ensues.
I also appreciate gentlemanly discourse on contentious topics.
Well done gentlemen. Well done.

What seems to be missing on one side of this discussion is logic. What does come through loud and clear is "sell sell sell".

The early divillar studs certainly failed. I've heard of stories of brand new engines still in the build process having studs break. But the later version 993 studs are superior in every way.

But use some logic here. I'm sure these super studs do not break, but that doesn't make them the only choice. Any one could make a stud that would not break if the correct engineering was imputed. I would argue that a stud made by ARP in one of these low horse power engines would not break. Not all studs are made from the same material. You choose the material for the job at hand. An ARP stud made from their aged 625 steel would be a complete overkill here. In a Turbo engine producing 3 times what these engine produce it would be a good choice.

Later model cup engines making just under 500 HP seem to last without breaking studs and these studs are not these super studs. They are the later version divillar studs.

Choose your studs for the engine use. It easy to use a stud that is overkill for risk management reasons. No argument here on that. But to infer that unless you use them your engine may fail is nonsense. That just comes across as a fear tactic to push sales.

Nothing has being mentioned about assembly procedures. You fit a threaded insert into the case, use these super studs and torque down the nuts either by angle or a torque value. It doesn't matter how good the stud is, how strong the insert is when the head collapses inwards around the stud underneath the head washer. How good is any stud now if the tensile stretch that was supposed to go into the stud is now compromised by the head collapsing.

I'm with those that want to use whatever stud they wish as long as the stud is up to the job at hand and proper assembly procedures are used. Fear is no way to sell a part. Good advice is and good advice typically offers options without pushing one over the other just to make a sale.

^^ I don't think any 911 engine stud has failed from being too weak from a design standpoint. It seems to me they are all issues due to corrosion, especially of the early uncoated austenitic stainless steel ones.

The bigger issue as has been stated is the stud pulling out of the expensive, NLA engine case. 911 engines seem to run fine with broken studs and they can be replaced but the case is a bit more difficult.

Didn't the 917 or RSR use Titanium studs?