Can Dilavar head studs be safely re-used?

[chris_seven]

Originally Posted by Henry Schmidt

We never build engines with Dilivar so my suggestion is to throw away any of these studs you have.....new or used....
Just my 2 cents worth.


BTW: Chris, I have seen band new factory Dilivar studs break after installing them on a rebuilt engine before the engine ever runs.
The last time it happened, I had to call a customer to tell him his 356 show car had a dented drivers side quarter panel.

Henry,

I am sad to say this argument is just becoming religious in nature and after a lifetime working as a Metallurgist I am an unbeliever and find it very difficult to disregard all of the basic science. I would say that my interest in this debate is mostly academic as we never use Dilavar studs - new or old and in this respect I do agree with Henry.

I am sure you have seen a stud fail in this way and it has been commonly reported but I don't believe that studs that fail in this way have been genuine Dilavar.

The only mechanism that can create this type of failure is Hydrogen Embrittlement and the material used is reported to be Dilavar Ni13 which has a typical Nickel content of 13%.

12.5% is the normal level for the Nickel content of stainless steels that are considered to be insensitive to HE.

It is also interesting to note that it has never been reported that standard steel studs fail in this manner but the materials used for their construction are much more susceptible to HE as they will be a high strength ferritic steel.

Normally HE only affects plated fasteners but acid pickling is another potential cause of this problem but it is so unlikely that is can be discounted.

If the 'Dilavar' used has been incorrectly, manufactured and retains a significant amount of delta ferrite in its structure then it could become susceptible to the effects of pickling.

This would mean for a Dilavar stud to be sensitive to HE two mistakes are required.

The resulting part would also tend to be magnetic and although sold as Dilavar the stud is being incorrectly described.

If anyone has a stud that has failed in this manner I would be grateful for the opportunity to inspect and analyse the material.

[theiceman]

Originally Posted by Flat6pac

Once you torque them don't put on the valve covers.
Come back in the morning and see how many pieces are on the floor
Bruce

as i read over many threads trying to be informed about such things i can honestly say this did make me laugh out loud .

[boosted79]

double post

[boosted79]

Of course they can be reused. I made a punch out of one.

[tmaull]

You could use it to stir cocktails. It'd be quite the conversation piece.

[Tippy]

Originally Posted by boosted79

Of course they can be reused. I made a punch out of one.

LOL, I'm sure it shattered after one blow?

[theiceman]

hhmmmm trying to think for a re-use for these.



one broke on its own triggering the repair and the other three broke on removal. actually two of them broke while mounting the engine on the stand of all things. I mounted the engine eon the stand and rotated it to check movement and two fell out.

[Flat6pac]

I remember a friend ordering like 12 dozen, years ago, and when they arrived there was a couple in the box broken. You never know
Put a couple cuts diagonally on the threads and use it to clean the threads in the hole.
Bruce

[boosted79]

LOL, I'm sure it shattered after one blow?

It has to be used with a rubber hammer.

[john walker's workshop]

There was a bad batch many years ago that had breakage issues soon after torquing. Pretty common knowledge around here. No issues lately.

[jellonailer]

I will bring this back to the top, just to continue the controversy.

Rebuilding my 3.0 due to 4 cylinders with large leak down, 50%. That was a surprise as were a few others - my pistons had 4 broken 1st rings (not so much due to leak down numbers), cylinders are Nikasil and perfect, and my studs are Dilavar both top and bottom. This group is pretty opinionated about changing out the head studs. I talked to a well know 40 year, air cooled, P-car engine builder/mechanic and mentioned I would be changing them to steel. He looked at me like I had 3 heads and asked why, of course re-use them.

I'm scratching my head now...

[Trackrash]

All the science and talk in the world don't change the facts. These were original '78 studs.

My '71 on the other hand still has its steel studs, no problems with them.

[911pcar]

Not to totally exonerate the mixed reviews of Dilavar as the ideal head stud compatible with the expansion rates of the non-ferous parts clamped by it, but one can also take the position (in your case) that, "if it ain't broke, don't fix (or replace) it."

I'm fairly certain there are severall thousand 911s still running around with healthy (and intact) Dilavar studs (real ones, not knockoffs). Again YMMV. Perhaps the German foundry and PAG engineers have finally met the threshold of their designed objectives with the latest iteration (Ver. 5 or is it 6?). Maybe their engineering//metallurgy sights were set higher than merely compromising with a quite adequate alternative (steel) and instead continued to perfect an ideal material truly compatible with their design philosophy. But then again, that's just my WAG or maybe PAG's engineers were just bull-headed, determined to be right in the long run. Both reasons sound pretty equivalent.

BTW, anecdotally, the all black Dilavars in my long departed RS spec 2.7 were last seen intact. However, the engine had only ticked over a mere 27k miles in 15 years before it sailed away to its current owner. Hardly a long term testimonial, but a little better than 24 hrs. after initial assembly as some have reported early on.

Sherwood

[Rawknees'Turbo]

Originally Posted by jellonailer

I will bring this back to the top, just to continue the controversy.

Rebuilding my 3.0 due to 4 cylinders with large leak down, 50%. That was a surprise as were a few others - my pistons had 4 broken 1st rings (not so much due to leak down numbers), cylinders are Nikasil and perfect, and my studs are Dilavar both top and bottom. This group is pretty opinionated about changing out the head studs. I talked to a well know 40 year, air cooled, P-car engine builder/mechanic and mentioned I would be changing them to steel. He looked at me like I had 3 heads and asked why, of course re-use them.

I'm scratching my head now...

There is just too much evidence out there supporting the idea that it is a sound practice to replace the Dilivar head studs, regardless of if any of the current ones are broken or not (+/- 40 years worth of evidence, including volumes of it on the Pelican forums), to defer to the experiences of one mechanic (even if he is the god-of-fark when it comes to Porsche engines ). I've got a couple of longtime friends in the area that have over 20 years, professional experience each with Porsche, aircooled engines, and they would give you that same three-headed look if you told them you were considering NOT replacing the studs.

[Alan L]

To summarise the discussion which has had screeds posted on this forum; in theory, from a metallurgical point of view, Dilivar are the superior technology and should not fail. Porsche probably thought they were doing a smart thing installing them. Years of experience showed there is an issue which seems to come down to an underestimation of the corrosion factor. At which point they quickly become the worst option.
Why would you continue with old studs while you have the chance to replace them? Everything has a life span and the Dilivars seem dubious.
Alan

[chris_seven]

The problem with Stress Corrosion Cracking and any other type of environmentally assisted fatigue failure is that there is generally little or no warning of impending doom.

The parts works well one second and then 'bang' and the component fails in a brittle manner.

The chance of inspecting a component of this type and finding a 'sub-critical' defect is negligible and this is why metal fatigue is such an invidious process.

I can't think of any NDT technique that could be used to check a Dilavar stud and find the very, very short defects that will cause the failures we experience.

Many critical aircraft parts are simply replaced as being 'time expired' for exactly this reason.

If anyone thinks that you a crazy for replacing components that suffer from well documented failures I would respectfully suggest that they haven't quite understood the issues.

[al lkosmal]

This is my 3rd 3.0 in a row (this year) with broken studs..................

I was tearing this 1980 3.0 down today.......5 broken studs. (the one circled in red will be a bugger to get out)

If you like Dilavar, I've got a bunch of them for you.......special deal.







regards,
al

[Alan L]

I have had one or two like that. I have welded the broken stud back on in one case and I think a nut in another. Then LOTS of heat. (I am sure you know this) When it gets hot enough you don't need a huge amount of torque to free them - just enough to be able to rotate them free. Just keep feeling the torque, keep heating and wait for it to ping free. And hold your breath, I find it helps for me.
Alan

[MST0118]

I chose the supertec studs for my 2.8 motor based on a 7r mag case but I think ARP should work fine, too.

[Henry Schmidt]

What a nightmare.
With Supertec Head Studs, you will never have a head stud issue again.
Plus you get the added bonus of easy installation.
You can actually install the piston and cylinder as an assembly without struggling to install the pin and clips.
Do it once and you'll never assemble a 911 engine the old way again.






Supertec Heads Studs are the number one selling head studs on Pelican Parts for a reason! Try them and you'll see why.