Help me diagnose why my head gasket blew

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JGC403

JGC403

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I want to figure out why it let go. No point in putting it back togeather with new gaskets and it happening again. Engine is a Magnum 360, with stroker crank, Edelbrock aluminum heads.

Cylinder #8 was filling with water.

Head gasket and bolts:


Looks like that is where it failed, part of the fire ring is MIA:


Why are the bolts so greasy:


does the missing blue line on the Fel Pro gasket mean anything, another leak?



A lot of carbon build up:


Cylinder #8 on left:


Eddy head, valves and plugs are red because of octane booster, I think.


More carbon build up along the edge of the combustion chamber on the head:
 
Detonation? What was the plug gap, timing (initial & total)? I could be wrong, but the only time I've seen firing rings disappear were from engine's that were detonating.

Our crap pump fuel here in CO tends to leave red in the combustion chambers, but I'd never use an octane booster.
 
It would ping going up hill in high gear. Thats why I put octane booster in, seemed to help.

PCM controls timing. Plug gap was stock for 5.9, or if Edelbrock recommended one with that head.
 
I always skip on using that part # head gasket, I use the 8553 or the 1008's.
Looks like the fire ring burned away., but the pics are being viewed on my cell...

Whats the compression ratio?

And can you set the head gasket on the block so I can see where the fire ring ends up?
 
Did this happen after a rebuild a little while ago? Were the head bolts torqued properly? Are the decks and heads flat?
 
I thought Alu heads helped with pinging , what was compression ratio and what grade/octane gas do you use ?
I get pinging going uphill in high gear if the revs are under 2500, always drop it in 2nd if possible .
 
Compression 10.1:1
Everything was torqued correctly when I built the engine.
I use the highest octane fuel I can get at the pump here in PA, I don't remember what it is exactly though, 93?

The head is flat checked it with a machinist straight edge.
 
JGC403 said:
Compression 10.1:1
Everything was torqued correctly when I built the engine.
I use the highest octane fuel I can get at the pump here in PA, I don't remember what it is exactly though, 93?

The head is flat checked it with a machinist straight edge.
Click to expand...

That's the same compression mine has , I was thinking of getting the Alu heads so I'd stop the pinging ,maybe run a lower grade gas , using 94 octane now . Guess it's not that much help .
Now you have me worried that the detonation could do the same on mine . Damn
 
Bolts would be greasy if who ever put it together used moly lube which i hope they did. Just a thought if the pistons came out of the hole you may be above 10 to 1
 
72ScampTramp said:
Bolts would be greasy if who ever put it together used moly lube which i hope they did. Just a thought if the pistons came out of the hole you may be above 10 to 1
Click to expand...

Yes, I used Moly on all of the bolts. But some are dry and some look like they were submerged in oil.

Compression should be 10.1:1
 
Sounds more like almost 11.1 ,to be 10.1 piston needs to be IN the hole more then 0.15 and piston volume needs to be a little more then +5.00........and gasket thickness
counts too.............................
 
Pistons come out of the hole and aren't all the same:

#8=0.009"
#6=0.007"
#4=0.016"
#3=0.017"
 
Check to see if the dowel pins are too long (holding head up slightly)
 
JGC403 said:
Pistons come out of the hole and aren't all the same:

#8=0.009"
#6=0.007"
#4=0.016"
#3=0.017"
Click to expand...

Sounds like the rods aren't all the same length, which is common with resizing done by a novice or factory production type machinist. Performance shops , some, will find the shortest rod and match the rest...or better yet, get a longer rod...also can sometimes get away with removing more from the cap side ...say surface the cap .005 and the rod .002....but anyways..lol
Along with rod length varying ...the block is probably sloped front to back.

Don't worry about that too much at this point unless your quench is set to where only a couple pistons actually provide a usable quench distance...that would explain the detonation. Check quench distance! Jmo
 
1wild&crazyguy said:
Sounds like the rods aren't all the same length, which is common with resizing done by a novice or factory production type machinist.
Click to expand...

That is what I was thinking also. They are aftermarket rods though, K1 H-beams, If I remember correctly. I think it was something that I would of had to ask to have done, with the machinist I took it to.
 
JGC403 said:
That is what I was thinking also. They are aftermarket rods though, K1 H-beams, If I remember correctly. I think it was something that I would of had to ask to have done, with the machinist I took it to.
Click to expand...

Even good quality aftermarket rods (like K1) can vary. Stroke equalization is pretty important, imo. That combined with an uneven deck will throw off your compression. If it were me, I wouldn't just throw head gaskets back on it, and run it.
 
I had the block square decked. So the deck "should be even side to side, front to back.

I don't have the money to completely tear it down and have part corrected. So the only thing I really can do is put new gaskets on maybe slightly thicker ones to help lower compression and not reduce quench to much.
 
Did you have the crankshaft ground, it looks like the stroke is off.
 
what about just having the rods checked out, and resized if needed?
 
OLDSTYLE said:
Did you have the crankshaft ground, it looks like the stroke is off.
Click to expand...

Brand new stroker crank.

Louie70Dart said:
what about just having the rods checked out, and resized if needed?
Click to expand...

Don't have the time right now I need to get it back on the road. Once I get my shifter mechanism back from Passion, I can get my Duster on the road, then I can park this one and work on the engine.
 
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