745, your image is only visible if logged into tdiclub. Might want to try hosting it locally.
The one that pulled threads was previously compromised and repaired; however, to me it's noteworthy that the thread repair had held with no problems until the last engine failure (not related to HG), and that there were no problems in reaching installation torque or re-torque when the motor was being assembled. Also relevant that the head studs have (by design) substantially increased tensile strength vs the stock bolts, so at the point when you'd be necking and then breaking a stock headbolt, with a stud we see increasing force on the block threads and increasing squeeze on the gasket -- two things we have evidence of in the autopsy here. The fact that it's possible (or perhaps all too easy) to destroy stock headbolts without hurting the block doesn't mean that the same is true with studs -- we have no certainty that in an extreme situation, the fastener is going to always yield before the block does. Of course this is kind of the whole idea with studs, and I suspect the use of studs here perhaps accounts for why the HG didn't pop much sooner, *during* the overheat events (of which there were multiple), rather than 500 miles further on down the line. In any case I don't think you need to exceed torque spec in order to put a pretty wild amount of force on the head fasteners, head expansion alone is more than enough to do that. I've had heads off a couple that got too hot where several of the head bolts were loose -- like I could spin them out with my fingertips.
IIRC Raceware does provide a length spec, which would probably be interesting to check. I suppose you could also put a caliper on the headgasket just to get a clue as to how hard it got squished. But to me the big picture is that we seem to be seeing multiple failures that are all attributable to repeated exposure to massive heat. A Helicoil is the correct repair to damaged head bolt threads and is not a cause for major concern when exposed to operating conditions and forces within the intended "normal" realm... The fact that it apparently failed here, to me, doesn't mean it was an inappropriate repair or that it would not continue to be appropriate going forward, merely that in this case it got put to a test it was never designed for. Bears keeping in mind that the HG blew on the other end of the head from where the stud pulled out. I see both as separate "effects" of a problem rather than "causes" - IMHO anyway.
