So, was it ever determined what, exactly, caused the ARP rod bolt to fail? Was it overtorqued? Was there a defect? It would be very unusual to find a manufacturing defect in that bolt...

Rob,

Maybe Tristan will chime in on this one, but having been with him for most of the assembly, I doubt it was overtorqued. More than likely it was defective.

I'll extend an offer to whoever has the bolt, if it's still available: Send me *really* good close up pics of the fracture surface (both of them) and I'll do my best to tell you what's going on. Better yet, contact me offline and mail me the bolt and I'll examine it here, with our metallurgist who specializes in failure analysis, and we'll try to diagnose the cause. And then I'll return the bolt.

I'm motivated; I have ARPs in my engine too...

Rob,

The bolt never fractured, it just "stretched" to the point where it was obvious that it was failing.

I would still love to see an independent metalurgical analysis performed on it.

You and me both. If one sent to a consumer can fail, how does one check...

Oh, that's right. I forgot that you didn't actually fracture the bolt. Well, there's still the potential for plenty to be learned by an examination, if you're interested. There are various tests that can be conducted, some of which are destructive (metallography to examine microstructure and chemical analysis to evaluate the chemical makeup and proportion of alloying elements). It's possible that just a visual, nondestructive exam under an optical microscope, and maybe a hardness test, will tell a lot about what has happened. Let me know if you're interested.

I'll forward to the "owner" of the bolt. :)

for entertainment,
Jim Sims posted some interesting info

"deburred using a powered hand held emery wheel (something like a Dremel tool). Below is an image of a silver plated (for clean thread lubrication) MP35N alloy screw with safety wire holes. This is among the best fasteners our civilization knows how to make: 260,000 psi strength and very corrosion resistant - it will function in seawater and at liquid nitrogen temperatures. Expensive as sin (35% colbalt); the bolt shown was $136. If one orders the best "aerospace alloy" engine rod bolts, etc. this is the alloy one is likely to get, although some of the vendors may be switching to the almost as good but cheaper Carpenter 625. Happy preloading!"

http://forums.pelicanparts.com/showthread.php?s=&threadid=163097&perpage=20&highl ight=schnorr&pagenumber=2

http://forums.pelicanparts.com/uploa...1105450165.jpg

SPS Carrillo rod bolts are made of the same mp35n alloy, the best rod bolt on the planet!

Lookit those threads! Smooth as boobies. :p

I always hate to put the SPS bolts back in my Carillo rods, I just like to just sit and look at them, they are a work of art.