The coatings look great, I will have to try them, pretty local to me, but whats up with shipping those heads out of state? I usually get the Michigan head work?? Just kidding, Mark does a great job! :)

That's def not short trips....my SC gets to temp in about 10 miles in the summer.
I've a friend that is a pro wrench and he's seeing the same thing with 964 dilivars...the 'new improved' studs are breaking just like that. Many low mile cars too.
The only place he puts dilivar studs is in the trash bin.

Should be a dif wth 993 studs.

Lol

The difficulty is trying to understand the 'mechanism' that would cause failures of this type.

I have been involved in the study of engineering materials behaviour for more years than I am prepared to admit and have reasonable understanding of the Fracture, Fatigue and Creep behaviour of metals and it is really difficult to explain this behaviour.

The failure of the original Dilavar Studs due to Stress Corrosion Cracking (SCC) is a classical failure mechanism for High Strength Austenitic Stainless steels and older cars that were being used on salty roads is the most likely cause of failure.

We have seen a number of broken Dilavar studs of this type and they do seem to show the effects of intergranular corrosion that would initiate these failures.

Unfortunately I no longer have day to day access to a Scanning Electron Microscope to be 100% sure but I believe this is the main cause of the main issues with these studs.

The later coated studs should help to eliminate this problems as the coating should prevent the corrosion that initiates the subsequent brittle fracture.

There is also significant evidence that Dilavar studs fail due to the effects of Hydrogen Embrittlement (HE) and this is confusing.

I cannot understand why DilavarNi13 should be susceptible to the effects of HE as everything about the composition and nature of this alloy would indicate that it should be suitable for use in environments where atomic hydrogen is present.

The only conclusion is that there are non-genuine studs in the supply chain that have an incorrect chemistry and that have been badly made and have picked up hydrogen during the manufacturing process.

(We do know that some non-genuine studs have been available due to 'Magnetic Dilavar' studs have been routinely advertised. There are also some A286 Studs available which are powder coated as this material will be prone to SCC when used 'raw'.)

The working environment would not cause failure due to HE and some as studs are reported to have failed prior to use but just due to being tightened, it is clear that they must contain manufacturing defects.

The increased stress in the stud when expansion occurs during warm up may tend to increase the likleyhood of brittle fracture if there is hydrogen present in the steel but this would tend to be more dependent on time at temperature rather than due to any thermal cycling. This is the failure type that I can't currently understand.

It is an interesting problem but the cost of trying to understand all of the reported failures would be extremely high and apart from curiosity probably not worthwhile.

The effect of hydrogen on fatigue crack initiation is not very well understood but it can never be good news so I would tend to avoid aftermarket Dilavar studs.

I can't see any real reason why a good quality Dilavar stud with the correct composition and heat treatment should be a problem but I am not sure that they are of much benefit other then on old magnesium cases.

This car in the 25 years I had it never seen salt. And they were genuine Porsche parts from Sonnen when they were replaced in 1998-1999. I wish I had taken Paul Weir's advice and went with the steel. I started out doing a valve adjustment..... and then....