your opinion on head studs

[Trakrat]

I'm undecided on what to do here.

I've been reading Wayne's books religiously as I've been disassembling my engine.
So with that in mind, I've discovered that a PO had replaced the studs on my case with 993 Divalar studs... at least they look like it due to the threads nearly on the entire studs.

They also look fairly new... meaning no rust or discoloration on the stud itself.

So here's my dilemma that I need your opinion on.
I had already budgeted on getting Raceware studs, as I didn't expect to find these 993 studs in the case.
I don't know anything about who or how these studs were installed. As far as I know, the builder may not have even put the correct loctite on the threads.
But most of all, I don't know WHEN these studs were installed.
Finally, I need to ship most of my engine components, including the case to a machine ship in AZ to do the cleaning and machining. I'm not sure how studs hold up to being cleaned in a hot tank, much less taking the abuse of a UPS/FedEx carrier during shipping.

Now, going back to Wayne's books... he states many times that divalar studs tend to break and to replace them no matter what. Soooo... what would you do?

[jackb911]

The 993 studs are said to be a big improvement over what was used prior to the 993, But I used ARP studs when my 3.2 Carrera broke a head stud a few years back. I'm a big fan of ARP fasteners - absolutely bulletproof stuff.

[Catorce]

Ditch the dilavar. Go steel, ARP, or Raceware.

[Bob Kontak]

Originally Posted by Trakrat

But most of all, I don't know WHEN these studs were installed.

Take pics of the studs and post. Assess feedback as to what they are.

"All thread" studs are highly recommended.

However, in 1997, I sprung for Raceware and the coolest part was spending the $125 (then) for the nuts. Torquing them to 25 ft lbs was like butter.

As sweet as Raceware, ARP, Supertec may be, if you have adequate coverage now, that's a lot of money to pay for insurance you may not need.

[boyt911sc]

Trakrat,

Remove the cylinder head studs and send your crankcase to the rebuilder. When the crankcase comes back, decide if you want to stay with the Dilavars or not. I could lend you a the Snap-On stud remover. It would take you about an hour to remove all 24 studs with an impact wrench. Keep us posted.

Tony

[DanielDudley]

I would always err to the side of caution, but steel studs will work as well as high priced spread.

You budgeted for a replacement set. Don't second guess yourself.

[gomezoneill]

Originally Posted by DanielDudley

I would always err to the side of caution, but steel studs will work as well as high priced spread.

You budgeted for a replacement set. Don't second guess yourself.

Like this guy say's don't waste your money on arp or raceware unless your building a race engine. Steel is plenty strong enough.

[KTL]

FYI the last 993 non-turbo engine used all steel studs. Part number is 993-101-172-02, superseded to 03 and is now shown as NLA by Pelican. But dealer websites show the 03 is available at around $25 each. I know for certain these are available because I bought some awhile back. Pelican also has the standard steel studs for $12 each, part number 911-101-172-00

So I don't know if that matters to you or not but it indicates to me that the all steel choice is an entirely reasonable one for a 3.2, be it a "stock" rebuild or one hotted up. Granted the 993 is a little bit different with the special turbo alloy heads (RR360 material, I believe?) and ceramic head port liners. Regardless, folks have gone with the standard steel studs on these older engines for many years with no ill effects.

Go with the standard steel studs and save yourself some money that you can put toward something else. Clean up the all thread 993 studs and put them on the classifieds. Somebody will want them.

[KTL]

BTW here's what the steel 993 studs look like

Steel Head Studs, Barrel Nuts & Washers

Reason I sold them is because the engine they came from got hosed, by me, and I chose not to rebuild it, parting it out instead.

[RDM]

Originally Posted by KTL

Pelican also has the standard steel studs for $12 each, part number 911-101-172-00

Go with the standard steel studs and save yourself some money that you can put toward something else. Clean up the all thread 993 studs and put them on the classifieds. Somebody will want them.

Wisdom here. I went with the Supertec studs, but in retrospect the straight up steel ones would have been just as good.

[Koizumi]

Well, I’m happy with my Supertecs after all these years.

[DanielDudley]

Originally Posted by Koizumi

Well, I’m happy with my Supertecs after all these years.

Why wouldn't you be ?

[Trakrat]

Well... most likely I may be having to replace these head studs as divalar is apparently known to break and even Ollies said that anytime they see divalar studs, they toss them and recommend them to be replaced.

[theiceman]

I put steel in my stock 3.0 litre and never thought twice about it.

and in other great news , once you put steel in you will no longer struggle with Dilavar spelling

[Trakrat]

Originally Posted by theiceman

and in other great news , once you put steel in you will no longer struggle with Dilavar spelling

Ha! no wonder my searches hardly find anything.

[chris_seven]

The failure of early Dilavar Studs is due to a very straightforward mechanism.

Dilavar is a Precipitation Hardening Austentic Stainless Steel which suffers from intergranular corrosion in the presence of chlorides such as Salt.

The grain boundary corrosion behaves rather like a crack and as the defect extends into the stud the remaining area reduces and the stresses created by cylinder expansion causes a failure.

This mechanism is known as Stress Corrosion Cracking (SCC) and is common in Marine and Petrochemical environments.

The resin coating applied to the later Dilavar studs does create a barrier and providing the coating is undamaged will work well.

The other aspect to consider is the use of the car. If it not driven on salted winter roads then there will not be any intergranular corrosion and failure then becomes very unlikely.

A286 is a common fastener material used in the hot section of Jet Fighter engines with great success and is similar to Dilavar and unsuitable for use in chloride bearing situations.

There is some apocryphal evidence that Dilavar also suffers from Hydrogen Embrittlement but I find this idea very unlikely.

Austenitic Stainless are not considered to be susceptible to this type of failure and IMHO the Molybdenum content of Dilavar should eliminate all risk.

I tend to believe the idea that a significant of 'spurious' studs found their way into the supply chain and were so badly manufactured from poor quality materials which did suffer from HE.


If 'your' Dilavar Studs are genuine Porsche parts and the coating is undamaged I would use them without concern.

If you don't use the car on salted winter roads the chance of failure is virtually non-existent.

This is a statement currently being made and is very confusing and concerns aftermarket 'Dilavar' Studs:

That exhaust leak you hear in your 911 may actually be the cylinder head leaking where the studs have pulled loose. As Porsche increased displacement of the 911 engine, the different rates of thermal expansion have caused head studs to break or pull out from engine case. These latest aftermarket steel head studs have a thermal expansion rate of approximately the same as the alloy case. Unlike original Dilivar material our studs are made in the USA and are magnetic.

The section I have highlighted is really confusing and needs some explanation as the only conclusion is that these studs may be made from a Duplex Stainless Steel

Steels with 'high expansion' always have a crystal structure which is Face-Centred Cubic - Known commonly as Austenite. Their Coefficient of expansion is around 18 x 10^-6 mm/mm/degK. These steels are ALWAYS non-magnetic.

Conventional high strength steels are typically Body-Centred Cubic structures which have been heat treated but still retain a basic Ferritic or Martensitic structure.
Their Coefficient of Expansion is typically 11 x 10^-6 mm/mm/degK.
These steels are ALWAYS magnetic.

There is a new family of materials known as Duplex or Super Duplex Steels and they are used for fasteners when good corrosion resistance is needed along with reasonable strength at a lower cost than an Austenitic Material.

They have a structure that tends to be 50/50 Austenite/Ferrite but their Coefficient of Expansion is around 12.5 x 10^-6 mm/mm/degK. They will also be magnetic.

Their strength (Nitronic 19D) is also limited to around 115 ksi which I think is marginal when used on an engine with Aluminium cylinders and would not be an obvious choice.

[Trakrat]

Originally Posted by chris_seven

If 'your' Dilavar Studs are genuine Porsche parts and the coating is undamaged I would use them without concern.

Then the question is... how do I determine if its an original Porsche part?

[theiceman]

and it is very likely the coating will be damaged if they are removed and reinstalled no ?

[bpu699]

Search this site...

Not that I would ever go out and buy 993 dilivars, but you already have them.

There were threads on here that rate them higher than raceware/arp...

True or not, I have no idea...

My understanding is that 993 fully threaded dilivars are NOT the same as standard dilivars...

When it comes to replacing the studs, I went through the same dilemma...

Steel vs Super tech... Bought the supertech...

Stock rod bolts or ARP? Got the ARP

Money no object, get the good stuff... But at some point you will need to decide for yourself what isn't necessary...

I did the mental math, and if you want to go full out on everything, the cost skyrockets pretty fast...

I can totally see how guys spend $10-15k on parts and machine work... and then lets not forget labor...

[bpu699]

Originally Posted by theiceman

and it is very likely the coating will be damaged if they are removed and reinstalled no ?

How hard would it be to paint or powder coat the shaft if you scratch it?

If you try to remove the headstuds, you risk damaging them. The question is do you leave them in as is, or go another direction...