Genuine 911 Steel Studs from a Porsche Dealer in the UK are about $15.00 each.
We have used them in a number of 3.0SC engine with good results and as the expansion characteristics are virtually identical to any other Ferritic Steels the pull out forces due to expansion shouldn't be an issue.
The 7.6mm shank diameter is also a benefit in terms of pull out force compared to some other studs but this doesn't seem to be much of an issue unless we are considering Magnesium Cases.
The aspect of the standard steel stud that I like is the 'Class' or fit of the thread.
Most after market studs seem to use a 'commercial' of standard fit for the thread and this is a looser fit that that used by Porsche so there is less 'rock' or misalignment as the threadlocker sets when using a standard stud.
Again possibly not a major issue but a point in their favour at a relatively low cost.
We always clean case threads with a simple 'chaser' we never use a plug tap or any other tap that can reform the thread as this always reduces the class of fit and the studs ultimate load holding capability.
I am not sure why 993 Dilavar studs are fully threaded but the coating is designed to prevent corrosion pitting that can be caused by chlorides and is certainly responsible for many of the early failures of these studs.
The current 993 studs appear to be fully rolled and then have a small hexagon in the centre but we have never used any so this is just how they appear in photographs.
I have recently seen some A286 Studs being advertised at $14.99 each and these studs are said to painted
They are advertised as having the same Coefficient of Expansion as Dilavar but they are said to be magnetic.
Sadly someone doesn't know enough about metallurgy and there are some contradictions in the statements being made.
1. For a steel to have a high expansion it needs to be an Austenitic Grade.
A286 is a Precipitation Hardening Austenitic Stainless Steel used in High Temperature environments such as fighter aircraft engines.
2. Austenitic Steels are always Non-Magnetic. There is no way to make a magnetic version of A286 - it will always be Austenitic and never become magnetic.
If a stud is magnetic it is not made from an Austenitic Steel and Vice Versa.
In reality A286 has a permeability of around 1.02 which means it has a very small amount of retained ferrite in its structure and a minimal amount of residual magnetism.
It is classed as non-magnetic for all practical purposes and I can't imagine Dilavar having a lower amount of residual magnetism.
3. I cannot imagine A286 being less costly than Dilavar and would expect it to be significantly more expensive - the low price makes me worry
4. When used in a Chloride environment (salty roads) A286 does suffer from corrosion pitting and this could result in failure due to stress corrosion cracking.
When used in Marine environments it is recommended that the strength of the material is restricted to a tensile strength of about 120ksi which means it yield strength will only be 90ksi.
I would estimate that this means that the studs would be close to their yield point on a hot engine.
If it is used in a higher strength condition to provide a better safety factor they will potentially crack when used in salty conditions.
Even in its strongest condition it is only around 20% stronger and is not the best choice for a head stud.
The main reason this alloy is used is that it has great properties and oxidation resistance at 1300degF.
I wouldn't use A286 'Magnetic' Studs even if I were paid.
