Headstuds - would you use these?

[MatthewBrum]

There seems to be two rule of thought..

1) Dilivar has the same expansion rate as aluminum therefore less stress on the studs & case. Less of a chance for the studs to loosen over a number of heat cycles.

2) High quality steel stud that has modified thread pitch & longer threads into the case. Finer thread pitch means more clamping load enough to overcome any differences in thermal expansion and heat cycles.

The problem I have with the dilivar studs is that if the rate of expansion is close to that of aluminum then everything would grow the same if the heat evenly. But I THINK that there is no way the cylinder and the studs are the same temp while the engine is under load.

If this is the case why dilivar? ...just my thoughts

[J P Stein]

Take a close look at the close up pic of the threads of the studs in the first post.
Those are J type rolled threads. The root of the thread has a U shaped radius rather than a V shape cut.....tho a J type thread can be cut. That is as good as engineering gets on threads.

[Henry Schmidt]

Originally Posted by J P Stein

Take a close look at the close up pic of the threads of the studs in the first post.
Those are J type rolled threads. The root of the thread has a U shaped radius rather than a V shape cut.....tho a J type thread can be cut. That is as good as engineering gets on threads.

All good Porsche head studs have rolled threads not cut. The key to top quality threads is whether the material is heated treated prior to rolling the threads or after. Supertec head studs are heat treated, aged, then ground to size (three separate grindings). The threads are then rolled.
That just leaves the the nut. There couldn't be a goofier head nut than the allen barrel used by Porsche. With the Supertec stud, you get the best quality nut manufactured by Porsche. A hardened, grade 12, serrated flange 12 point nut. This nut is without question the best Porsche factory nut money can buy. The use of a 12 point nut means there is no clearance issues with twin plug heads and stud install height no longer matters. That allows us to make the case thread end longer so you can run the thread in the case for maximum thread engagement.

[J P Stein]

I an't looking for a fight, Henry. I recall you saying that your studs have the same thermal expansion as aluminum (or close) That's good enuff for me. If I ever need any some, I'll give you a call. I bought the 993 divilar 10 years back (for cheep) & they are still going strong.

[andrew15]

Originally Posted by Henry Schmidt

That just leaves the the nut. There couldn't be a goofier head nut than the allen barrel used by Porsche. With the Supertec stud, you get the best quality nut manufactured by Porsche. A hardened, grade 12, serrated flange 12 point nut. This nut is without question the best Porsche factory nut money can buy. The use of a 12 point nut means there is no clearance issues with twin plug heads and stud install height no longer matters. That allows us to make the case thread end longer so you can run the thread in the case for maximum thread engagement.

Henry's put a ton of work into these studs and it shows in the small details - finer thread pitch on the head fastening end, lower profile 12 pt nuts, heck - even the packing was nice with a small tube of locktite
I used them in a twinplugged 2.6 - easy install and no plug clearance issues with the 12 pt nuts. The engine has been running strong for a couple of years now with no issues.

Regards,
Andrew M

[docrodg]

Originally Posted by Steve@Rennsport

LOL,.......No harm, no foul.

I have "no dog in this hunt" and I'm not selling studs to anyone besides our engine customers, of course. We simply use & recommend what we think to be the best components for a specific application, based on our experiences over the past 33+ years.

To be fair, we've not used the Supertech head studs as of yet simply due to our successes with the late 993TT studs (same as RSR/GT-2). There is no question that these Dilavars cannot be compared to the early Dilavars which were prone to corrosion and soon after, failures. Since we cannot afford a problem with a customer's engine, we tend to use solutions that we know from experience will be durable and reliable over the long term. R&D and new product evaluations are normally done on our own personal equipment or when a customer consents to being the "guinea pig" in such rare circumstances.

We've had similair problems using ARP head studs due to their inability to remain torqued under high heat and rates of expansion. Having discovered far too many loose head nuts using these, we stick to either steel ones for the early small motors and the late Dilavars for the larger bore and turbo engines.

Now,..................some thoughts about these subjects,............

I think its worth noting that rarely are such issues totally black & white. Ultimately, we are all the sum of our personal experiences and our thoughts and statements simply reflect our opinions about various things. Keeping this in mind helps maintain context (and hopefully civility) on such occasions such as postings in such forums.

JMHO, so YMMV,

Steve is right, we are the sum of our experiences. And is also trying to be a calming voice in this storm of controversy (go post on the oil thread!) I have used the steel studs in the past with no problems on engines in Porsche and other models. In addition, I have used ARP Studs in very high performance aluminum block drag and circle track racers on Chevy v-8 small and big blocks due to HP well over 800 (one busted 1000 HP! wheee!!) and no problems. The choice is based on what you believe is required in strength, and information available on what you are using.

That being said, I spoke with a manufacturer of bolts that I know through work and his responses were interesting:

All companies producing bolts will test the materials and the bolts, which are all engineered to some degree. Any bolts that are for high stress/high grade required applications get substantial engineering conducted including thread stress resistance, stretch at used torque and temperature in use, tensile and other mechanical strength testing like Durometer, and others. It is the simple grade 1 bolts that are not engineered to a great degree. This engineering is then verified and validated for the intended use as required by ISO9001:2008 and TS16949. The studs and nuts themselves are tested both as raw stock, formed, and then final after heat treat and everything is finished. These tests are conducted on samples from each run randomly as they are produced, to eliminate a potential of not detecting a periodic manufacturing flaw as a simple "every 100th part" sampling can miss a flaw that occurs every 40th part. Some may do time or part number based sampling but they do not. Nuts get the same treatment, and the whole unit is tested at varying nut positions for overall strength. Durometer and other testing is done as well, both on the shaft and the thread. New design validation also includes environmental testing for corrosion resistance and imposed weakness in elevated aging tests (salt water baths at elevated temperatures and concentrations that turn years into weeks).

As to Dilivar: He really had no input, as it is rarely used and has issues in general as an alloy in it's reaction to certain conditions.

This is a case where you need to look at the question carefully and form an answer based upon substantial statistical evidence - a sample size of 4 people who have used these studs without issues is not significant. The rate of failure is reportedly high so that may be the conservative approach to use without direct evidence of the failure rate in the "newer studs" as opposed to all dilivar studs. The 4 people stating they are fine is like the people who say they do not wear a seatbelt because they have two friends that survived a rollover or other bad accident only because they were ejected from the car... statistically that is stupid, as the proven numbers show that 98% of ejected victims die in car crashes.

[Henry Schmidt]

Originally Posted by docrodg

Steve is right, we are the sum of our experiences. And is also trying to be a calming voice in this storm of controversy (go post on the oil thread!) I have used the steel studs in the past with no problems on engines in Porsche and other models. In addition, I have used ARP Studs in very high performance aluminum block drag and circle track racers on Chevy v-8 small and big blocks due to HP well over 800 (one busted 1000 HP! wheee!!) and no problems. The choice is based on what you believe is required in strength, and information available on what you are using.

That being said, I spoke with a manufacturer of bolts that I know through work and his responses were interesting:

All companies producing bolts will test the materials and the bolts, which are all engineered to some degree. Any bolts that are for high stress/high grade required applications get substantial engineering conducted including thread stress resistance, stretch at used torque and temperature in use, tensile and other mechanical strength testing like Durometer, and others. It is the simple grade 1 bolts that are not engineered to a great degree. This engineering is then verified and validated for the intended use as required by ISO9001:2008 and TS16949. The studs and nuts themselves are tested both as raw stock, formed, and then final after heat treat and everything is finished. These tests are conducted on samples from each run randomly as they are produced, to eliminate a potential of not detecting a periodic manufacturing flaw as a simple "every 100th part" sampling can miss a flaw that occurs every 40th part. Some may do time or part number based sampling but they do not. Nuts get the same treatment, and the whole unit is tested at varying nut positions for overall strength. Durometer and other testing is done as well, both on the shaft and the thread. New design validation also includes environmental testing for corrosion resistance and imposed weakness in elevated aging tests (salt water baths at elevated temperatures and concentrations that turn years into weeks).

As to Dilivar: He really had no input, as it is rarely used and has issues in general as an alloy in it's reaction to certain conditions.

This is a case where you need to look at the question carefully and form an answer based upon substantial statistical evidence - a sample size of 4 people who have used these studs without issues is not significant. The rate of failure is reportedly high so that may be the conservative approach to use without direct evidence of the failure rate in the "newer studs" as opposed to all dilivar studs. The 4 people stating they are fine is like the people who say they do not wear a seatbelt because they have two friends that survived a rollover or other bad accident only because they were ejected from the car... statistically that is stupid, as the proven numbers show that 98% of ejected victims die in car crashes.

The sampling of 4 you mention is only the 4 who chimed in. Supertec head studs have been installed in over 300 engines over the last 7 years with NO issues reported. That is "0". Most of these engines were high performance engines requiring the highest quality parts available. Does every engine need "the best"? of course not. The quality of the parts you choose is up to you.

Side note: anyone wanting (used) Dilivar studs can have them for free. While supplies last. Just pay $15.00 packing fee and actual. shipping. They come with a guarantee. I guarantee that they are crap.

[docrodg]

Originally Posted by Henry Schmidt

The sampling of 4 you mention is only the 4 who chimed in.

That was exactly my point, it is only those who spoke, and that is not a good sampling. Many good studs are out there, and you choose your preference. With the history of the Dilivar studs we have it is probable that they are failure prone overall, so the choice seems to be Aftermarket Studs (those that are known to have good records in this market are Supertec, ARP, and Raceware), or factory steel. Here the choice is based on perceived stresses that they will see, personal preference, and size of wallet. Aftermarket tend to be somewhat more expensive, as the production runs are not at as high a volume.

Personally, I believe that these forums should not be used for promotion of one's own products; or they should be confined to the parts forum. No disrespect or anything, just a personal opinion. If your product is good then rely on the people who have used it to post their comments - although I admit that complaints are far more common for people to voice than praise. A simple note that your product is available is IMHO fine, "commercials" are not what these forums are about (again, personal viewpoint, and others are welcome to disagree).

As I stated in my post, all manufacturers conduct engineering of these products, and they use modern practices, especially in the case of those compliant to TS16949 as they are therefore required to conduct PFMEA and FMEA analysis along with lifecycle analysis and aging of the parts with subsequent testing. The problem with the stock Dilivar studs is that the practices for engineering at the time they were made were not as thorough, resulting in the failures of Dilivar studs that are so famous. Newer studs are not handicapped by this issue, but, are not made of Dilivar. I spoke with a couple of metallurgists but they were not knowledgeable of the alloy so no dice there... but I would love to find information regarding the alloy and just why they have these issues.

Please understand, I am not questioning the quality of your parts, especially since I have not used them, or the integrity of your business. Nor am I attempting to "attack" or "flame" you in any way. In fact, I have heard good things about the studs you offer, and would consider them as equals to the other known aftermarket high performance ones available on the market.

[Henry Schmidt]

The purpose of my post was to answer the question. "Headstuds- would you use these?"
The question could be answered with a simple no or even Hell no! but generally members on this forum want to know why. Of course my answers are only my opinion but with well over 400 911 engines under my belt I guess my opinion carries some weight. Who knows?

I offer a great deal of advise to members on this forum and if stating that one of my products might be a better choice violates your sensibilities then I apologize.

[docrodg]

F'ng hell no to DIlivar!

No need to apologize, as no offense taken on anything here. As I stated, mention is not an issue to me, it just seems that when more than a "check these out" post is done it is like a commercial in the middle of a good movie. Some of the posts were more commercial like, but to each their own.

As far as commercials...Too bad Billy Mays died... a few commercials on P-car parts could have been funny!

[JFairman]

If you're putting all that time and money into a high power engine then another $500-$700 for brand new top quality studs, washers, and nuts seems minimal and logical.

Parts of those 993TT studs look odd. They look like they've been used.

Why do they thread almost the entire length?

[motley911]

I am pretty sure that the studs have never been used. They were new and installed into the cases some years ago but the engine assembly was never finished. Initially I thought they were pieces of all-thread and not head studs at all. I did some research and found that 993 studs are fully threaded but also made of dilavar. They have some sort of epoxy coating on the middle portion of the stud which makes them look strange.

The dilavar material is what raised my concerns. Quoting from Bruce Anderson's 911 Performance handbook:
"Another problem that has occurred with the Dilavar head studs over the past few years is their failure right after an engine is assembled. One mechanic told me that he had just torqued up the heads and was walking out of the room when he heard a loud Ka-ping noise and something bouncing off the wall."

"I started getting regular reports on these missiles flying through people workshops"

It was this sort of quote that raised my concerns and prompted me to post the question in the first place. I can understand / tolerate if the studs fail after some years due to corrosion however premature failure due to poor material properties is something different. Although it doesn't seem that any of the people who have posted on this thread have experienced failures right after assembly.

Thanks to everyone for their input,
Richard.

[mamut]

Originally Posted by JFairman

If you're putting all that time and money into a high power engine then another $500-$700 for brand new top quality studs, washers, and nuts seems minimal and logical.

Parts of those 993TT studs look odd. They look like they've been used.

Why do they thread almost the entire length?

My guess is that they are threaded for a better location of the stud in the bores, it is a tighter fit, they are fatter, this allows for less movement of the heads and cyls.,

[Flieger]

I think the almost full thread would move the location of the stress riser where the stud body transitions to the threads. This weak spot could be in a better location such as a vibrational node or away from the head/cylinder sealing boundary where there may be more shear loading.

[chris_seven]

Great debate all of which is interesting and metaurgically quite fascinating but I think it is quite straightforward to sum up the basics.

It is quite clear that there were significant problems with studs pulling out of casings and this was probably due to a number of different effects.

Someone in an earlier post calculated that for a temperature increase of 200 degF the stress in the bolts of the engine would increase by about 30000 psi. ( they also calculated that this equated to around a ton of force on each bolt but it is stress which is doing the damage)

The effect of this is that the mean stress in both the bolt and the material surrounding the thread must be closer to failure. Each combustion cycle then produces a fatigue stress in the bolts which is superimposed on the mean stress due to clamping and expansion.

The BMEP of a high performance petrol engine at peak torque is probably about 10bar. This results in a load of around 1400lbs on the head (90mm bore) which is an additional stress of about 4600 psi.

All very damaging from a fatigue perspective.

If we now add to this a magnesium casing which is probably losing both strength and ductility with time due to overaging and it is not surprising that studs were pulling out of cases.

The mean stress due to the expansion was probably the killer as high levels of mean stress have a very dramatic effect on fatigue life.

The use of a controlled expansion alloy would significantly reduce the mean stress and greatly reduce the likelyhood of fatigue induced failures.

It is very difficult to find any good information about Dilivar but is seems that due to its non-magnetic nature and its relatively high expansion (About 1.7-1.8 greater that ferritic or martensitic steels) it must be an Austenitic Stainless Steel.

These steels are generally considered to be very sensitive to Stress Corrosion Cracking particulalry when heated to over 80 deg F and in the prescence of Chlorides. (Salty Roads?)

Not really the greatest choice of material.

This family of materials is also very prone to the content of sulphur and phosphorous during manufacture and as there seems to be virtually no other commercial application of this material it must be made in very small batches which implies that ther may well have been serious process control problems in the early days.

The new coatings have clearly been developed to eliminate SCC and I am sure that modern process control has improved the batch to batch performance but in my view it is still not a great material as any damage to the coating will re-iontroduce our old friend SCC.

Now most crankcases are Alusil and these alloys are much more stable than the Elektron family of Magnesium alloys (1969 remember) I believe pulled studs are now very rare and we can re-evaluate.

I would, in general agree with Henry, and select a base line material that doesn't suffer form SCC at moderate temperatures. Precipitation Hardened Martensitic Stainless steels that don't suffer from SCC are available in strength of up to 250ksi for use in Aero Gas turbines and should be excellent. If the studs are then manufactured following best practice then this must be the ideal solution.

Dilivar must at best be a 'sticking plaster' to solve other problems otherwise this type of alloy would be in widespread use throughout the engineering world.

I have spent a considerable time trying to find good data about Dilivar and spent hours seaching my local University libraries database but without success.

i would really like to find a detailed analysis - other than 13% Nickel so that I could understand the detailed metallurgy and form a better view.

[kenikh]

My 2 cents - Detractors regarding product promotion aside, you cannot argue with the value the engineering detail in Henry's posts add to this thread. The fact that the efforts and love regarding the details of engineering are shared here should be a story unto itself - I don't see ARP or Raceware here, day-by-day, adding to the debate and knowledge base.

BTW, I know for fact that the number of installs and failure rate numbers are 100% true. With all of the detail that went into the engineering of Henry's studs, I know where my money is going.

This site is for knowledge sharing and debate. That is exactly what I see above.

[Shaun @ Tru6]

Originally Posted by motley911

I am pretty sure that the studs have never been used. They were new and installed into the cases some years ago but the engine assembly was never finished. Initially I thought they were pieces of all-thread and not head studs at all. I did some research and found that 993 studs are fully threaded but also made of dilavar. They have some sort of epoxy coating on the middle portion of the stud which makes them look strange.



Thanks to everyone for their input,
Richard.

hi Richard, would you like to sell your 993 studs? I'm building a sports purpose 3.0 and these would make a good addition to the build. Started pulling my existing studs tonight. Please let me know.

Shaun

Anyone have an opinion on 993 steel studs?

[lucittm]

I think it is important to remember in this discussion that we are compressing forty years of Porsche's attempt to remedy a design flaw inherent in the boxer engine - the temperature induced expansion and contraction of almost 36 inches of magnesium and various other metals and then aluminum from one side of the boxer style engine to the other.

According to the Anderson book (p. 58) there were 5 types of dilivar studs up through 1987 and the current dilivar stud, the fully threaded 993-101-170-53-M260 is Porsche's latest attempt to engineer a solution. ANY dilivar stud prior to this version is not recomended for the reasons mentioned in the above posts. But don't lump all the dilivar studs into the same category.

Clearly the aftermarket manufacturers responded to the dilemma that Porsche faced and many head stud products are now available from ARP, Supertec, Raceware, Canyon, Casper Labs, and others. Price, reputation, recommendation, and experience will determine each person's choice when selecting replacement or upgrade head studs.

As a case in point, I have OEM steel head studs in my 964 turbo and they are shown as P/N 10-0115-101-M105 in the PP list (but NLA in the parts diagram). They are similar to the studs used in the early 911 engines and were used in factory engines before the 993 dilivar studs became available.

This forum is the perfect place to exchange opinions and personal experiences. This is how we make our cars better and improve the aftermarket parts availability for all of us to select.

Thanks,
Mark

[JFairman]

The old BMW flat twin motorcycle engines were similar to half a 912 engine.
I know it doesn't apply here but the studs were steel and similar to but thicker than 911 studs and I never heard of them pulling out or breaking on those engines.

[K24madness]

Does anyone know if the 993NA and the 993TT share the same studs? Any concern about reusing a set that has 29k miles?