As some of you may recall, I had an unfortunate event recently where my intake manifold blew up (https://ls1tech.com/forums/forced-in...-manifold.html) Well, upon taking the heads off, I found a crack in the block by the water jacket by the #6 cylinder:



I am planning on replacing the shortblock with an iron 370 now, but I'd like to have an idea as to what caused the havoc in the first place so I can make sure it doesnt happen again on the new engine and BBK manifold. I also don't know if the crack developed when the manifold went or not. It has been leaking coolant since my current LS6 engine was almost brand new, but I know it wasnt cracked on the deck like that when I first got it. Just sucks because I only have like 5000ish miles on this engine

 

Dood, JB weld that thing and put it back in. I hear that water running on the outside of the engine cools it down even better.

Sorry to joke but seriously hopefully you get back up and running soon.

 

Is it really a crack? In the pic it looks like it was just scored. Sorry about the misfortune. One question though: why were you running the engine if you knew the coolant was leaking?

 

Yes, it is a crack for sure. I couldnt get a close up pic without the flash messing it up, and when I turned the flash off, it was all fuzzy and grainy lookin. But yes, its a crack for sure.

As far as why I was still driving it- I tried tracking down the leak several times and never found the source. I just attributed it to the 'pushing water' like what seems to be a common issue with forced induction. I had changed head gaskets a few times, and it never solved the issue. The sponsor I bought the block from didnt seem to want to help me much until I took the block out of the car and found the source of the leak for sure. I didnt have time to take the block out because I was overloaded with work and school and my spare time is spent sleeping since I didnt get much of that at night. PLUS, I didnt feel so motivated to take an engine out that I had JUST got done installing! At any rate, this is the situation I am in now, and I need to come up with a plan and make for damn sure this incident doesnt repeat itself.

 

So a shop assembled the block for you? Maybe the heads were warped or the deck was not leveled completely. Very strange that is for sure.

 

A shop assembled the shortblock. I put the heads on myself. I'm using ARP head studs too FWIW...

 

I would think it would have pushed coolant just driving around normally if it was cracked like that before your intake exploded.
Mine cracked #6 like that also. My only theorie with my block was from banging the rev limiter one too many times with a lot of meth still spraying = detonation.
I was at HKE the other day and Erik had a several aluminum blocks with cracked sleeves. I'm going iron also.

 

Ive done that twice but one time it was a stock motor that detonated... second time... 1000 rwhp for ~10000 miles on a forged shortblock... just gave up the ghost.

for your power level, I would say you detonated.

 

Thanks for the input guys. Tiago- you think simple detonation could have caused that and my manifold to explode? Sounds like a tall order to have happened especially with meth spraying and 0 KR showing on my interceptor gauge. But who knows.. I was actually wondering if maybe a spring was weak or something, but I don't know if that would have caused it or not either.

Man, I know what thats like. I cracked my stock LS1 block down in the sleeve like that... However, this crack in my LS6 block is not in the sleeve at all. It is actually in the aluminum part of the block. All the sleeves look great from what I can tell.

 

I wonder if it was just a casting imperfection that got worse with heat cycles? That is a strange place to crack. Maybe cylinder pressure caused the walls to expand and around the water jacket was the spot to give. That sucks man.

 

Yea I really don't know.. It sure is a weird place to crack. One thought my brother had was maybe it lifted the heads and pressurized the coolant system and acted like hydraulics somehow and cracked it?

 

When your intake blew out, were you in the throttle or letting off?

 

To the best of my recollection, I was still in the throttle, but it could have happened immediately after I let up. Its been a while.. I know it was at the top of 3rd gear and I was givin her hell..

 

I would think something else would have given out before the block cracked, but either way it is an odd crack.

 

Just thinking some...I'm wondering if the crack surfaced during that run, or the heads lifting enough to fill that cylinder with coolant, and when you let off, maybe it filled with steam and that popped the intake. Not sure if that is a possibility or not.

 

Is that crack the same place it was leaking coolant? If so maybe it could have been a slight imperfection in the block to begin with and finally let go under pressure.

 

I have no clue where the coolant leak was coming from. May have been from there, but I can't confirm it. I do have pics of the block when it was new fresh right out of the crate, and there isnt a crack there, but who knows if it was weak or not. Im almost leaning towards that direction myself (a weak flaw in the block to begin with) because honestly, I havent the slightest inkling as to how that crack could have got there in that particular location.

 

Detonation is far more likely than anything else.

 

More than likely you would of bent a connecting rod had that been what happened. I agree with the other post, it probably was from detonation. Bob

 

If you look @ the dark areas just between the cyl. and both of the water jackets. Looks like the head may have been lifting there.