Causes of engine block crack?

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matt030305

matt030305

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Just wanted to get some foresight on potential causes of a cracked block. Tore apart my motor today expecting a cracked head gasket since I was getting coolant in cylinder 3. Couldn’t find anything until I looked at the piston head and realized it’s completely destroyed, and that the blunder wall cracked into the cooling jacket. What could be the cause of this? Thanks FABO
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matt030305 said:
Just wanted to get some foresight on potential causes of a cracked block. Tore apart my motor today expecting a cracked head gasket since I was getting coolant in cylinder 3. Couldn’t find anything until I looked at the piston head and realized it’s completely destroyed, and that the blunder wall cracked into the cooling jacket. What could be the cause of this? Thanks FABOView attachment 1716330329View attachment 1716330330View attachment 1716330331View attachment 1716330332
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Sorry for your loss on this one, Dano. Hopefully you can have that sleeved to fix if you want to keep it. If not, maybe time to upgrade to a 408 stroker by Blueprint? Can't beat their warranty, and drop in and go. Had a bad engine in my 70 Duster so got the 408 from BPE and never looked back.
 
Ricks70Duster340 said:
Sorry for your loss on this one, Dano. Hopefully you can have that sleeved to fix if you want to keep it. If not, maybe time to upgrade to a 408 stroker by Blueprint? Can't beat their warranty, and drop in and go. Had a bad engine in my 70 Duster so got the 408 from BPE and never looked back.
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I was looking into that. I have everything for my top end rebuild specifically for an LA small block. I know oiling for the magnum blocks are vastly different. What modifications would I have to do to make a magnum blocks compatible with an LA top end?
 
That looks like a real thin spot in the casting, bust a piece off and the measure it.
 
matt030305 said:
Just wanted to get some foresight on potential causes of a cracked block. Tore apart my motor today expecting a cracked head gasket since I was getting coolant in cylinder 3. Couldn’t find anything until I looked at the piston head and realized it’s completely destroyed, and that the blunder wall cracked into the cooling jacket. What could be the cause of this? Thanks FABOView attachment 1716330329View attachment 1716330330View attachment 1716330331View attachment 1716330332
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You probably Scuff the piston, look at the skirt on that piston and see if it ain't all fucked up and cracked as well. Are those hypereutectic pistons? Looks like they are. Did you hear any dull knocking on that one?
Is it stock stroke? If it's a 4-in motor and you clearance the bottom of it cylinder bars maybe went a little too far and it got thin and cracked its way up is another bet
 
That looks to me like a broken ring land due to catastrophic knock or pre ignition which butts the rings. Hard to say what came first the broken piston or the cracked block but it’s a mess regardless.
Pistons breaking like that is very common in boosted stuff and it’s always related to cylinder pressure spikes and not enough ring gap.

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More than likely my son can fix it or replace it. "SK Machine" North East Pa. Its what he does. He is on this site all the time. You all just don't know who he is.
 
MOPAROFFICIAL said:
You probably Scuff the piston, look at the skirt on that piston and see if it ain't all fucked up and cracked as well. Are those hypereutectic pistons? Looks like they are. Did you hear any dull knocking on that one?
Is it stock stroke? If it's a 4-in motor and you clearance the bottom of it cylinder bars maybe went a little too far and it got thin and cracked its way up is another bet
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Stock stroke, took the motor out because I thought I blew a head gasket. Heard a bang and Started seeing white smoke come out of my exhaust pipe.
 
TT5.9mag said:
That looks to me like a broken ring land due to catastrophic knock or pre ignition which butts the rings. Hard to say what came first the broken piston or the cracked block but it’s a mess regardless.
Pistons breaking like that is very common in boosted stuff and it’s always related to cylinder pressure spikes and not enough ring gap.
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Could’ve been pre-ignition. Engine didn’t have any knock when it was running. But could that cause the cylinder wall to split like that? What came first? Cracked block or destroyed piston? Who knows
 
And from the looks of it, it was recently honed, did you just put this together recently?
 
replicaracer43 said:
And from the looks of it, it was recently honed, did you just put this together recently?
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Nope, previous owner did. Did quite a crappy job at it too. Many, many knucklehead things were done to the car that just didn’t make sense. Bellhousing bolts were all loose, flex plate bolts were all loose, crankshaft bolt was finger tight… I can go on and on…
 
Well, that opens up a whole slew of possibilities. First thing I would do is slide a piston out and check piston to wall clearance and ring end gap on a non broken cylinder. Then report back with your findings
 
replicaracer43 said:
Well, that opens up a whole slew of possibilities. First thing I would do is slide a piston out and check piston to wall clearance and ring end gap on a non broken cylinder. Then report back with your findings
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Will be reporting back. I was going to test fit all my top end parts I purchased. Seeing that it wasn’t a cracked head or head gasket Just put me in a sour mood.
 
matt030305 said:
Could’ve been pre-ignition. Engine didn’t have any knock when it was running. But could that cause the cylinder wall to split like that? What came first? Cracked block or destroyed piston? Who knows
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You're not going to crack a cylinder wall with some street pinging. If it was detonating.. it would be felt ar surging, coughing, and noise.

The hone looks rough enough to hold oil, so no overheating.
 
matt030305 said:
Will be reporting back. I was going to test fit all my top end parts I purchased. Seeing that it wasn’t a cracked head or head gasket Just put me in a sour mood.
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Totally get that! But it's a 340 block, so it has inherent value beyond any 360, and putting in 1 sleeve, then boring the block to the first oversize would be simple, and at MY shop, that wouldn't cost $1000
 
MOPAROFFICIAL said:
You're not going to crack a cylinder wall with some street pinging. If it was detonating.. it would be felt ar surging, coughing, and noise.

The hone looks rough enough to hold oil, so no overheating.
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Correct, but the piece of piston floating around in there can do some damage.
 
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