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Question Broken Dilivar Studs?? Root Cause?

I've seen a lot of posts lately, regarding the dilivar stud failures (and of course I've read Wayne's book, with regards to same) - I've got a question - Has anyone done an "autopsy" on some of these failed studs, to try to discover the root cause?
I know that there are many different failure modes for metals, but I've NOT ever heard of anyone doing the material science on these parts. (could it be hydrogen embrittlement, for example?)
Do we have any such expertise in the PP "brain trust"? If so, can we find one expert (or willing amatuer) who would perform some analyses on some failed studs?

I would think that some Pelicanites who have connections with universities or research labs, may be able to shed some light on the failure mechanism of these parts. It would make a decent 'senior project' for an aspiring materials science or mechanical engineering student...... what say you Pelicanheads? Any volunteers? I'll submit the first set of samples.

If we an understand the cause of the failures, then we could go about making informed decisions about what studs to use, and why.
Old 11-29-2003, 08:03 PM
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send me some broken ones, and i could forward them to my professor at UTEP. i took a class with him, in which we took various failed metal components and ran them through test to "find the cause" of the failure. this included some really cool work with an electron microscope. that is a great idea,joey. hey doesnt akron have a great mechanical engineering dept. i seem to remember being destroyed once by your university's mini baja team. once, only once.

cliff
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Old 11-29-2003, 11:00 PM
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I thought the cause was obvious. They corrode and then break at the resulting stress risers.
-Chris
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Old 11-30-2003, 04:50 AM
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the ends of the broken studs are black at the break, indicating a penetrating corrosion. the two places they break, are where they are exposed to the atmosphere at the head to cylinder joint, and between the cylinder base and the engine case. these areas generally have a rust ring around the stud. i've snapped some that were not broken yet, in the vise, and noticed the brownish/black penetration in the fresh break. the replacement black coated studs had a breaking problem about 10 years ago, which was deemed to be a bad batch. you're probably safe enough using new ones these days, and if they did break, it would probably be in 20 years or more. i still don't really trust them though, after all the problems.
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Old 11-30-2003, 01:37 PM
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I sent a broken stud up to the material lab at work but I haven't gotten a result yet. My non-specialist opinion is that it's stress corrosion cracking.
http://www.corrosion-doctors.org/Forms/scc.htm
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Old 11-30-2003, 04:14 PM
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Doesn't Wayne's book say that he has heard of brand new ones breaking on installation?
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Old 12-01-2003, 05:27 AM
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Corrosion. I can take a pick of my olds ones if you like? Even though my car's history has always been in the Texas/New Mexico area (where even non-galvanized cars seem to last forever), the dilavar studs i pulled out still have quite a bit of surface corrosion.
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Old 12-01-2003, 06:35 AM
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I concur on the corrosion. After pulling my this past weekend and closely examining them I was surprised to see how almost every one of the dilivars had corroded. 2 of them were so soft that I was able to bend them easily as I was twisting them out with the collett tool.
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Old 12-02-2003, 08:18 PM
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I can do a tensile test if anyone is interested. Might be interesting to compare Dilivar with steel...
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Old 12-03-2003, 08:00 AM
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That would be cool, for comparison purposes, use a new dilavar, an old corroded dilavar, and a steel one.
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Old 12-03-2003, 08:03 AM
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Talking Studs for Analysis are Shipped!

A set of studs have been shipped for anaylsis.
They are from my 1978 SC - 120K miles, OE studs sent to "UNFIXED"...who will have the analysis done.

I sent some steel, some dilivar - Steel are intact - dilivar's are the special "two piece" studs (hahahaha)..
I'll also contact local materials guys at Akron University and see if they are willing to do an autopsy on the remaining ones (total of 6 broken dilivar's )
I'll post results when we get them - Much thanks to Cliff ("unfixed" ) and the rest who showed interest...hope we can get to the bottom of this.
Old 12-11-2003, 06:38 PM
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According to Forbes Aird's "Racers Encyclopedia of Race Materials", Dilavar steel has a ultimate tensile strength (UTS) of around 180 ksi, pretty good stuff compared to other alloy steel fasteners on the market. In addition, he did offer that this was "in the temper chosen by Porsche." What does that mean? Can someone source this stuff in bulk for resale as OEM and specify a different temper from the manufacturer?

Not sure comparing a corroded Dilavar and a good steel is a fair comparison, but I'll trust you metal guys to know what's a straight up test.

Sherwood
Old 12-11-2003, 11:46 PM
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Yes, I have heard of new ones breaking on installation. There is a lot of debate out there on these studs, and I did a lot of research and asked a lot of people "in the know" for the book. The conclusion I came up with was to use the standard steel studs on all engines 1965-89, for both intake and exhaust. ARP and RaceWare are also good alternatives. I have no opinion yet on post 1989 motors...

-Wayne
Old 12-12-2003, 01:03 AM
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Wayne, are you sure that maybe some of the new ones that broke weren't rejects? In other words, the dilavars that i got, one had a nasty gash in it and i'm waiting for a replacement. And the gash happens to be right at the base of the stud just above the case threads (where i hear there's a lot of stress).
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Old 12-12-2003, 08:05 PM
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