Pre used head studs, bad idea...good idea ?

[3.0schotrod]

So I'm replacing the head studs on my 3.0sc, I was going to buy new racewear head studs but saw a set of used 993/996GT3 oem Porsche head studs for sale for less than half the price, pre used. It got me thinking, are pre used head studs compromised, stretched ??

If I assume (never assume right) that they were used 'normally, not over tightened in use, would it not be the same as re building my engine if it had perfectly good head studs and using them again, I mean newer design studs are fit and forget to some extent, tear it down and re use if you get what I mean

Or is it just a risky idea, thanks

[Flat6pac]

The GT3 head studs are the fully threaded dilivar 10mm, but, they're too long to use the cap nuts you have. Come up with a set of 10mm nuts with the 15mm shoulders you have it made for assembly.
The retail on these are about $17 each, not the $45 for the proper length 993 dilivar. if you're going used, pay accordingly.
Bruce

[304065]

Suppose you save $500 on head studs.

And then the engine lets go because one or more head studs have an issue.

Would you pay $500 to make the problem magically disappear? I certainly would.

So why not pay it up front and save yourself the R&R?

[chris_seven]

Why not just use standard Porsche steel studs they work well enough with a 3.0SC

[JFairman]

Originally Posted by 3.0schotrod

So I'm replacing the head studs on my 3.0sc, I was going to buy new racewear head studs but saw a set of used 993/996GT3 oem Porsche head studs for sale for less than half the price, pre used. It got me thinking, are pre used head studs compromised, stretched ??

If I assume (never assume right) that they were used 'normally, not over tightened in use, would it not be the same as re building my engine if it had perfectly good head studs and using them again, I mean newer design studs are fit and forget to some extent, tear it down and re use if you get what I mean

Or is it just a risky idea, thanks

Depends on the price and your Budget. I sold a used set of 24 Dilivar head struds for $50 shipped a year ago. They were in my 930 motor when I got the car. I used a Stahlwille .5" drive stud tool to remove them and it did a clean job of it.

12 were the smooth finish ones and they were the top row and the other 12 were 993TT fully threaded ones and they were in the bottom row.
All 24 of them wrapped in paper fit good in a small USPS flat rate priority mail box. The buyer was happy.

[3.0schotrod]

Thanks all for the advice. Its an interesting subject.

chris_seven, are the standard Porsche studs available for say $500 for a set of 24

Flat6pac, $17 each new is tempting, will look into that, but added nuts etc bumps it up

304065, I totally get what you are saying, its like scrimping and buying cheap tires right, is it worth it. But, I work in risk analysis, or at least part of my job is that subject, but its on subjects I have knowledge and understanding of. So I guess the question would be, what is the risk, to be able to know whether its worth taking a risk on anything, you have to know what the actual risks, effects and probabilities are.

I used to buy used tires, good brands, Michelin, Good Year, some friends used to say, I would never buy used tires, why take the risk (again what is the risk ?) I used to say, ever bought a used car, sure, they had, you immediately go out and buy 4 new tires ?, no you dont (well most people don't) You have no idea what those tires have gone through, yes car condition in general gives an idea, but you get what im talking about.

Maybe I buy a set of 24 for $800, but I want to understand what risk im taking if I pay half

[JFairman]

The risk is some of the used ones could break.
Look at the used ones you may buy first.. there is a satin black coating on them and if it's chipped or scratched away anywhere then corrosion could get started and lead to a stress riser in the metal. Then there is a greater risk of the stud breaking in that spot.

The used set of 24 I sold for $50 included the original Porsche Barrel nuts and washers. I even cleaned the rust off the the barrel nuts and washers in phosphoric acid and then sprayed them down with WD40 so they would look nice and not rust.
I don't think used dilivar head studs are worth much.

I used ARP head studs when putting the motor back together. I have more confidence in them.

[Flat6pac]

Just for reference, I build all the time for the street with steel studs. Most of the time I'm building because a dilivar, old style, stud has broken. Once the steel stud is in place there is no problem.
Bruce

[cabmandone]

When I put new studs in mine I had some suggest that I just put 12 used steel studs or even just 12 new steel studs in to save some money. I read some threads where guys used the old steel studs from someone like me that replaced all with new. My thought was if I'm going through the "fun" of replacing head studs I only wanted to do it once so I put in all new ARP's in my car.

[3.0schotrod]

And what im seeing is:

My current studs are original 1979 dilivar (bad spelling maybe)

Porsche 996 GT3 head studs are dilivar


But the GT3 studs are threaded all the way, mine only either end

So Porsche knew the material was not the greatest, was the re design (threaded all the way) the fix for the problem, or is anything dilivar a bad idea, however new they are ?

Thanks

[porterdog]

Originally Posted by 3.0schotrod

chris_seven, are the standard Porsche studs available for say $500 for a set of 24

Supertec full set from our host with nuts.... $637

[chris_seven]

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.

[3.0schotrod]

chris_seven (PM sent also)

Thanks for the detailed reply, so it looks like good old steel head studs may be the best balance of strength/life/cost, I see 2 products here on pelican parts

PEL-REBKT-03N steel replacement studs non painted at around $11 a piece

10-0115-101-M105 steel replacement studs painted at just over $16 a piece


If I buy un painted is it ok to paint myself, prime then paint, or is it worth the $5 extra, maybe they are powder coated or something. Studs are exposed somewhat to the elements.

Thanks

[porschemachinis]

nothing wrong with top (steel) syuds. remove the problematic bottom (dilivar) and replace with stock steel studs.

Cheers