It was Endurotech gasket. I'm wondering if the bigger diameter somehow gave it a foothold (like you said, a piece of material in there maybe) to burn across there.

I have a new Felpro gasket, 3.5" diameter, maybe I should try that?

Yeah, it looked like I had take a shear and cut that gap between #4 and #3, so clean...obviously that was burning through for awhile, it just went last Thursday as I drove to the train station, hence the rough running, those two cylinders were fighting each other. #4 was essentially dead, the exhaust port was wet, while the others were dry and gray. Also, #4 plug had obvious signs of ignition from two sides, so there was cross talk between the cylinders...ouch. It's a testament to the SL6's durability, I drove it home that way, cruised on the highway OK but no power to speak of, climbing up my hill to my house was awful, sounded like a hammer pounding in there; I figured a bent pushrod or something bad. All looks good except that gasket.

Question. I took it apart carefully, all the adjusters were tight, kept track of push rod placement, didn't turn the crank or anything. Can I just put it all back together and should be fine, right?

Yes, head bolts were tight, I had checked them when I set the valve lash last.

Brian

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none of the other rings in the gasket showed any signs of wear...I wonder if it was just a bad gasket...

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sure, you will still want to check valve lash since the new gasket is unlikely to crush to the exact same thickness as the old gasket.

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Right, but I can fire it up and do the lash hot, it should be close enough to put it back together and fire it up.

b

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The Felpro permatorque gaskets call for no sealant. Does anyone have experience with this, seems like if the head and deck are clean, freshly milled, one wouldn't need any sealant...

Anyone?

Brian

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That's the head gasket I'm using, and I've used it on two other engines. No sealant.

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If you Google "head gasket burn through" and look at images, you'll see many examples of this burn through pattern, i.e. between cylinders and also the look of corrosion of the gasket's rings...

I'd think there was a combustion issue, too hot or lean, but there's no sign of pitting in the pistons, their surfaces are fully intact, and the gasket rings at #1, #2, #5 and #6 show no signs of burning or corrosion whatsoever. In fact, it looks like it was only #4, it burned through and into #3 (but for the burn through point, #3 gasket ring was clean, not pitted or corroded). My AFR is good, not lean...very strange, must be the gasket had a flaw or debris stuck in there catalyzed the burn through, made hot spots.

b

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The surfaces were freshly milled in the rebuild and they appear quite flat, the head fits cleanly to the deck, I see no gap whatsoever. I think it was just the gasket failure.

What is that big hole just below the head bolt hole between #3 and #4? The gasket doesn't have a hole there...

http://s785.photobucket.com/user/67dart ... c.jpg.html

B

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That hole is an "artifact" left behind from the sand casting process.

It is called a "print", a place where the water jacket sand core was positioned, suspended & supported, outside of the cavity where the molten iron went.

The head gasket blocks this hole so the coolant goes all the way back to the rear of the block, then up into the head, to return to the front of the engine.
DD

Good to know that gasket is designed to block that hole and not flawed...

b

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The flatness of the block should be less than .006" when measured with straight edge and feeler gauge. If the space is too much , the gasket might
fail again

Detonation can be reduced or stopped by reduce timing. Small detonation
can barely be heard or felt but slowly damages gasket and other parts.

That corrosion on the gasket ring might have been caused by that tiny
coolant leaks on the intake manifold studs. Combined with detonation , it finally burn through the gasket.

Read your plugs for signs of detonation,make sure your torque wrench is accurate and make sure the head bolt threads are cleaned with a plug tap and the bolts aren't bottoming out a tad during assembly.

I zipped it back up and it fired up and runs great:

http://s785.photobucket.com/user/67dart ... r.jpg.html

I don't think the head bolts bottomed out, they weren't resisting like a bottom out bolt might. All the head bolts were good on the bottom, no signs of bottoming out previously.

I can see how that coolant leak from the head studs might have started the corrosion, good point. They don't leak any more, I fixed that right after break in.

It is really quiet and smooth now, I haven't road tested it yet. Idle is very smooth. I just warmed it up, got the coolant circulating good. Shut her down, did it again. Maybe 10 minutes of running so far. I'll take her around the block after a bit, I have to mow the grass now.

Thanks everyone for all your help.

Brian

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It still leaks under load....ugh. I put a straight edge on the deck and head, they looked really flat, when I mated the head and block, I didn't see any gaps, couldn't shine light through it...likely have to resurface one or both surfaces. How often does one get away with just resufacing the head? I'd hate to pull the engine.....again.

Anyway, on timing, I had set the timing to about 10 degrees advance without vacuum, that was at about 1000 rpm. Under 30 at high rpms. When I checked today it was higher, about 18 advanced, I dialed it back, but when I put in in gear I can't get it run smoothly, had to up the rpms.

What rpm values should I check timing at (without vacuum advance)?

Thanks,

Brian

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About 95% of the head gaskets I has used on slant sixes over the past 20+ years have been over the counter Fel-Pros. I might have used a Victor-Reinz a few times. I have NEVER had a sealing problem, even with my slovenly workspace and lackadaisical cleaning efforts.

Timing is checked at curb idle, around 700 RPM in park or neutral.

Can you get it to idle below 1000 RPM at all? What kind of vacuum are you pulling at idle? Do you have power brakes?

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