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745 TurboGreasel 06-08-2014 12:04 AM

My bad, one retorge was my instructons and what I did too...

If You'd run it over 100, i'd have figured overcrushing might be a possibility

Probably not


Is that a fiber gasket?
Is it all the cylinders?

Hecklebone 06-08-2014 10:09 AM

It is a one hole MLS gasket. All bores on the gasket have the damage that looks like crushing or heat with material missing. There is only the one bore o bore burn through, between cylinder 5 & 6.

v8volvo 06-08-2014 10:23 AM

Wow. What cylinders did the big blow happen between? Was it near the front of the head, close to the bolt hole where it pulled threads?

It never lost any coolant immediately prior to this incident?

Quote:

Originally Posted by 745 TurboGreasel
Is that a fiber gasket?
Is it all the cylinders?

MLS, a UK brand that I hadn't heard of before. Seemed well-constructed so we decided to put it in, given its easier availability vs a Reinz MLS. My understanding is that this motor has seen a lot of heat since it was put together so I suspect the gasket has lived a short but hard life; difficult to say whether these problems are the gasket's fault or not... The motor definitely got warm enough and yanked on the head studs hard enough to pull threads in one hole. However, seeing the way those fire rings are flaking apart I guess I might hedge the next time around, and stick with an Elring or Reinz fiber gasket or a Reinz MLS.

I would check the head surface carefully too -- it sounds like it didn't run very long after you started noticing symptoms, but the head surface might have gotten torched while it was blowing its way through those fire rings. Probably want to get it checked carefully for straightness too, given the history.

745 TurboGreasel 06-08-2014 12:48 PM

How smooth is the head surfacing? and was the old one blown in the same spot?

Hecklebone 06-08-2014 01:07 PM

Head seems fine, have not put a straight edge on it though. No pitting that i can see.
It has not done this previously. Last issue was timing cog coming off the crank.

745 TurboGreasel 06-08-2014 04:39 PM

I was wondering more about the surface finish, the MLS wants it quite a fit smoother than a fiber gasket.

v8volvo 06-09-2014 11:53 AM

Head was new, not cut.
http://d24t.com/showpost.php?p=7188&postcount=44

This gasket was unlike other D24 MLS gaskets. The Reinz gasket Volvo used to sell (9146007, 6008 etc) did not have fire ring inserts, it had the steel/rubber sandwich right up to the edge of the bore. This British gasket had inserts of a different material around the fire ring, similar to the composition gasket.

Regardless my guess is that extreme heat and resulting loss of clamping (due to either excessive gasket crush/damage, or fastener stretch, or both) is what's responsible for this failure. The initial torque process and subsequent retorque achieved spec torque on the nuts with no problems, yet at the point when Hecklebone removed the head after this latest failure, all the head fasteners were found to be below 40 ft-lb and at least one had pulled threads from the block. The head got hot enough that those fasteners got yanked on way hard, and I suspect the gasket's death was a result of that, no gasket is immune to failure when exposed to extreme operating conditions. I don't think it was exactly a fair test of this gasket's design, different though it may be. I've seen the other type of MLS gasket fail also.

However, I guess I would not condemn a decision to use a different gasket for the next round, since this failure doesn't fit the normal pattern even for fairly major HG failure in this motor.

745 TurboGreasel 06-10-2014 12:26 AM

Without going overboard on the torque, I'm having a hard time envisioning the studs pulling the threads out. I can break stretch bolts off all day and not hurt the block. I wonder if the block had some previous trauma?
Put those studs on a thread gauge, or maybe Raceware has a length spec.

I suppose the head getting hot enough could exert some pretty hefty pull, but I heated one up till it seized and the bolts seemed fine.
This is the surface it should have
http://i18.photobucket.com/albums/b1...psab178dd8.jpg

Are the corners burnt off the pistons or precup openings cracking?

Hecklebone 06-10-2014 05:49 AM

I think you are right about previous trauma. Two holes had been heli-coiled, one of those polled out.
Looks like they were done in the field, not perfectly straight.

v8volvo 06-10-2014 03:20 PM

745, your image is only visible if logged into tdiclub. Might want to try hosting it locally. :o

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. :p


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