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A while back ago a head gasket went while moderately getting on it in my car. I finally had time to get it apart and found some unexpected damage. My only guess is it lifted the head from the damage but I don't know how. The car has ARP studs. I'm not positive of the compression but I know its not outlandishly high cause it's got aftermarket dished pistons with valve reliefs. The heads have been milled but only enough to clean up the surfaces.

As far as I can tell the plugs look good. This was in the number 6 cyl. The only thing I knew that was wrong is the o2 sensor on that bank was dead. The boost is about 14-15lbs, 850cc injectors that were less than 80% dc. Any help would be much appreciated.


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Possible the head gasket was loosing pressure at that stop and the heat act like a torch.
Question is can it be cleaned and then use liquid steel to fill the gap or welded, then filed smooth ?
 

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I'm going to blame auto-incorrect for the atrocities committed here today.

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Possible the head gasket was loosing pressure at that stop and the heat act like a torch.
Question is can it be cleaned and then use liquid steel to fill the gap or welded, then filed smooth ?
Most people have it welded, the milled just to ensure the flat
 

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That is a head lift plus detonation since it is burnt through.

If it was part throttle it was likely tun related and you didn't have the fueling right. It needs to get into power enrichment and alot of tuners don't handle that part of the tune well on the dyno. It really needs to be street driven to get it right...
 

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What does the piston top look like for that cylinder? I find it hard to believe that a single event caused this.
What heads are those?
 

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what part number stud kit did you use or how much were they if they if they were under 200 there wrong if they were over 300 they are right
 

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Discussion Starter #13
What does the piston top look like for that cylinder? I find it hard to believe that a single event caused this.
What heads are those?
The piston looks fine. Just like the rest of them. They are LSA heads that have been worked

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Head lifted due to incorrect stud preload either due to incorrect stud length or not being torqued to the spec ARP demands (it's typically so much higher than the stock torque spec that people won't torque them to ARP's spec and therefore don't use up enough of the bolt stretch). The lifted head caused repeated high-pressure, high-temperature combustion to blow past the same spot and fire slotted the block. This used to be not all that uncommon on boosted motors. And, it looks like it still happens from time to time....
 

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Discussion Starter #16
Well after dropping the head off at the machine shop and talking to him he suspected it failed because the original shop that did the milling didn't get the surface perfectly smooth. If you look closely at the picture you can see a texture from the mill and it's actually something you can feel. He said when the head is like that the MLS gaskets can't seal properly. So according to that the head didn't lift.

Which makes sense because when it was on the dyno we heard what we thought was an exhaust leak so I replaced the header gasket and didn't notice a change. Unfortunately with inexperience on my part and the possible improper machining we missed something that could have been caught earlier.

Hindsight I wish I would have known better that the heads weren't perfect before I put them on but chalk it up to another expensive lesson.

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