SpeedyC2

My thoughts exactly.

I love following this saga, but don't have the chops to comment on the technical matters. It doesn't mean I'm not reading every post on this thread!

geolab

voila

Holger3.2

Hmm....
does not mention anything about the old ones or general replacement when used ?

'The new cylinder head stud can be used for individual replacement. It is not necessary to replace the cylinder head stud in groups'
For me, at least it doesn't says you can reuse them?
Any further info available?
.

SwayBar

Looking at your thread's link on the 993 Forum main page, currently there are:

posts = 437
views = 107,248

...so there are quite a few people keeping track of your progress.

Keep up the good work!

geolab

document intended to answer this...

Holger3.2

... never to old to learn new things ...

Yes, the document answers the question about the new studs, so he is right on that.
Still the question is if old or new studs have to be replaced or can be reused?
As an older guy, i assumed simple that is still the case as it was always on older engines. However ...
Just read through the workshop manual, to my surprise, it doesn't mentions anything about replacement of studs for reassembling.
And the manual is in general very specific about replacements of parts like nuts and bolts!

Still would put new ones ...

geolab

me too , what else
a micro corrosion as tiny as a needle tip will crack the stud in two

nothingbutgt3

Thank you kingroon, sometimes it's simply very frustrating, because each and other specialist has his own experience, records, philosophy, which is fascinating and appreciated (at least from me, talking in general) but when it is something about a way to choose for real, it is totally different.

I quite understand material properties, but experience most of the times overcomes theory.
what here is suggested is to change the studs because at the tightening torque they have been tightened and the stress they have been charged during the working cycles (material expansions and contractions), they would have overcome the elastic phase...but they basically should be torqued to stay in the elastic phase, not the anlestic, because otherwise they would go towards a stress breakdown while engine is running...so there is some space to tighten them again.

So, I must assume the prescribed tightening torque when the engine was built by porsche was designed to make the studs work in the elastic part of the material.

it is an unpredictable thing: who suggest to change them is for staying on the safe side, avoiding uncertainty.
but there are other uncertainity: are you sure the studs produced nowadays are same quality of the ones installed back in 1995?
Secondary, but not really, removing the old studs, it is a delicate process, while now the studs are exactly in the same position where Porsche installed them.

I think retightening would shear the material closer to the anelastic condition, butnoone can say how much.

But these are just my thoughts shared

nothingbutgt3

geolab

your mechanic must have read a few posts here , and I don't assume I am a mechanic to give you advice
don't take my advice!
porsche produced Dilavar head studs, and at one point, they issued the technical bulletin and started using steel with the document above
but for strong engines RS CUP etc, they produced a new dilavar stud
TODAY, porsche germany superceeded the steel head studs for all 993 to dilavar studs
if it was me ....
your magnetic studs who sat in water are not good anymore , a microscopic grain of rust in the metal, will pop the stud, since your car was in water
use the technical bulletin for measuring the studs
993.101.172.02 is magnetic
and 993.101.170.51 non magnetic dilivar, only one left now to buy
mind you dilavar steel alloy will rust too, and your mechanic has an old experience, and I am sure at least he knows good 993 stuff. But things change

Churchill

I've built a couple 993 motors and have seen a bunch more getting built, and have never heard of changing out the head studs. I've never heard of changing out head studs on any air-cooled 911 engine unless they're the old-school dilavar material, and those get changed not because they've been torqued but because they corrode and then break.

nothingbutgt3

These are very interesting informations, thank you geolab

But also your words are very clear Churchill, thank you.

So after your very technical and statistical contributes, I knew what to google, and I found a very interesting post on the pelican Forum about HE and Chlorid effect over Dilavar and Austenitic Steel, and the impossibility to check one by one the studs, because basically the defect would be practically invisible.

Experience seems to say steel is much better than old dilavar, whike new dilavar probably is as good as steel, so I am asking myself: approaching the change of all the studs, why should one go for dilavar instead of steel?

probably the mechanic checked the studs with a magnet because late 993 models had the new version of dilavar studs...

Now, the statistic says that no steel studs had broken after reusing them, but mine would be the only one that would have been underwater for more than 4 years, there is no stat available for such a case, it is a single case file.

If it were a standad engine rebuild with steel studs, after a careful check of their condition, I probably would choose not to change them without worries.

In this case, it is the first time one jumps from an airplane with the first ever prototype of a parachute...the unknown after almost 20 years of perfectly running service is not in the material of the studs, but in the 4 years environmental exposure underwater.

I think we could try also to figure it out, back analysing the effect of the water of that precise river over other components of the car, to maybe desume something regarding the studs status, more than a visual or instrumental inspection, an environmental one, from the way other components got damaged.

But it would be also important to know what is the price of very good replacement studs set, in both the versions, steel from a very good producer (probably my first choice) and dilavar from Porsche.

I am still asking myself what is the point of dilavar: is it lighter, is it more elastic?

- Magnesium melted, but all that was in electrolitic contact with it, i.e. the engine block and also the studs, was no less than perfect

- The crankshaft has no sign of corrosion, but just something on the coupling flange where it mates the flywheel (the part out of the block, inside the clutch/flywheel housing)

- The rods, each one of them, are perfect

- So are the camshafts and the shafts, all made of steel.

- And the studs, all the studs, are looking like brand new.

When I opened and disassembled the engine, the seats of the nuts, where fullfilled of silt almost as hard as stone, and after having carefully removed it from each seat, I could untighten the studs just using the wrench, no heating. The threads of the nuts didnt melt, they showed just a bit of corrosion, I was surprised about this specific aspect, the torx insert was working perfectly.

The same ease was while removing the other studs that take the two halves of the engine block together: are they made of steel or dilavar?

- The alluminum alloy of the engine block has been very few corroded, I would say something very superficial and in very few points, while the gearbox housing a bit more (more surface interested and in few points a bit deeper).

So I made myself the idea that aluminum and steel parts that were in very good electrolitic contact with magnesium parts (engine fan and fan housing) had no corrosion at all (steel) or very superficial corrosion (aluminum), but between engine and gearbox there is a sealing, so the corrosion was a bit more.

The other surpising part is that the knock sensor magnesium mounting brackets are perfect: this is very strange, and it could mean only that while engine fan was exposed to water flow, they were not, and they are in the lower part of the engine.

so, if the magnesium mounting brackets are perfect and are the closer part to the lower and deep part of the engine, where crankshaft and rods are perfect, camshafts are perfect, why should the studs not be the same?

The gears of the gearbox had cementation damaged in multiple points, as much as crown wheel, and the conical part mating it, while the primary and secondary shafts, the forks, shafts, etc. are without corrosion.
they started to have some surface rust when and if exposed to the air by the disassembling process.
Synchro rings looks perfect, as much as the dog teeth.

But I remember that when I removed the studs, almost 2 years ago, they didn't have any sign of surface rust at all.

The other question is: if one or more studs fail, what is the consequence?
Is there some kind of warning, symptom, noise that is produced when and if this happens?

Holger3.2

Wow
didn't realized that a discussion about studs could get 'which oil is the right one' qualities

I scrolled through other forums (mostly in German) on this topic and was surprised about the discussions there. Its mostly about older engines but often also with remarks to the 'newer' 993 studs from Porsche.
What would be the right or wrong thing to do is mostly spread like oil recommendations. Also i was surprised that stud failure isn't that rear as I thought.
Quintessence is mostly reached on the source of broken studs, its when the car is not or only seldom used, its simple corrosion; seems this mostly on Dilavar studs(the old ones!)!
Another point in regards to steel or Dilavar is also the magnesium case of older SC's ... but for other reasons.
Unfortunately, there are no hints what effect such failed stud has to the engine or how you would recognize it.
If for renewal, most of the guys go back to steel studs, but a lot also to Porsche's 'new' Dilavar studs.
There are even recommendations for steel for the 'low' studs and Dilavar for the 'high' ones. However, I didn't bother to ask what they mean with that...

So in my opinion, everybody should do what he thinks he is most comfortable with.
For myself, I did new studs on my rebuild (which is hopefully finished soon)

Edit:
just talked to my mechanic, he recommends Dilavar only, and (that's a new one in the discussion) exchange studs on opened engines if the studs are older than 15 years.

cobalt

My intention wasn't to offend or mislead anyone. I was just trying to help. I know there are many following. I started reading this thread in disbelief but have been intrigued and impressed by what you have found and clearly the results speak for themselves. I have seen earlier 964 head studs fail there is a noise associated with it. Sounds like a rattling although it has been a long time since I have seen one so far only on the earlier 964 engines with the early style heads made from a different alloy which might have expanded differently. The last one was on a 90 C4 engine I owned and it had 4 broken studs at 83k miles. When removed there were no signs of corrosion or anything I would consider a visible stress riser. I had a set of 96 993 head studs I pulled from my 96 993 engine and I switched to ARP and had thought long about using the later 996 head studs that are threaded nearly 100%. The picture is from a 996 Cup car engine you can see the studs I was considering. This engine has Ti connecting rods which will be replaced as they age out over time.





I guess let's discuss the concept.

Basic definition.
Torque-To-Yield Bolts
Once they reach this zone, they maintain a more precise and consistent level of clamping force across the entire head-to-block mating surface. The bolts are stretched into their elastic range, and in many cases, the stretching approaches the bolts' elastic limit, permanently stretching it.


When you install your connecting rods the bolts are torqued and rotated 90 degrees. These are clearly stretch to yield and are required to be replaced per the engine manual. So why wouldn't that same principle apply here? I use a gage to install the ARP bolts and they have indents on the top and bottom so you can measure the elongation. I agree the manual doesn't say to replace the head studs which I found odd. There are threads on Pelican saying no problem just reuse them although I personally would not and know of rebuilds that a stud broke after a few thousand miles of reusing the original studs. It might have been a fluke but why chance it the cost is so minimal. When I inspected the old studs there was what I saw as a slight deformation of the stud and located differently along the length. Part of my prior life I spent a lot of time pulling tensile test bars to verify the yield, tensile and elongation of a specific material. Unfortunately there is no way to determine if any elongation has occurred unless we measure, install and remove a new stud and measure it again. To me the indent would suggest plastic deformation from how it was manufactured. Weather this was from tightening or hard use being an N/A converted to turbocharged engine I couldn't say. Why Porsche chose to do what they did I couldn't tell you. I understand you want to reuse as much as possible although IMO for the small expense associated I personally wouldn't reuse them and see it as cheap insurance. Clearly some materials were well preserved and others did not survive 4 years of being under water. How this has impacted the studs would be hard to tell. We see how the other materials were affected and I suspect on a microscopic level there will be evidence of some impact.

I am sorry to take this off to a tangent, Just a suggestion I thought might be helpful.

nothingbutgt3

Thank you Cobalt, I don't understand if you are referring to me when you say that your intention wasn't to offend or mislead, I didn't get your words that way at all.
It is possible the way I express myself in English sometimes isn't correct, some other time it is also possible I am sometimes too much direct, but I am here in a very simple and for real way, but not just to accept and that's it, I would like to understand and take a decision conscious of what I am going through.

When you say ARP, is it a producer or an achronym?
The studs are now steel, if I replace them, as a consequence of what I've read so far, I think I am more for brand new steel one instead of dilavar version, and I have no idea what's the cost of the 2 solutions
Maybe there are different types made of steel?

What are the other studs you were talking about, upper part, lower part?!
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