Alright, we need some help here guys. I helped my buddy Allen (Z00) install a set of 6.0L heads and a TR 227/224 cam in his 2000 Z28 about a month and half ago. The install went fine with no major "gotchas". Then after driving the car about 100 miles, he experienced all the symptoms of a blown head gasket. Allen tore the heads back off the car and found that, indeed, the head gasket had blown on the #1 cylinder. We assumed that we must have hydrolocked a head bolt and that caused the gasket to blow.

So Allen started working on getting the block and heads ready to reinstall while we waited on new head gaskets, bolts, etc. As Allen was cleaning the heads, he found a crack in the driver side head. The crack is between the #1 and #3 cylinders.

<img src="http://andy.speedgeeks.org/OtherImages/08.15.02-Allen_Heads/DSC00001_700.JPG" alt=" - " />

<img src="http://andy.speedgeeks.org/OtherImages/08.15.02-Allen_Heads/DSC00010_700.JPG" alt=" - " />

Wow, okay, so maybe the blown head gasket caused the head to overheat and caused the crack. I could buy that....maybe.

BUT, Allen then turned his attention to the passenger side head. Holy crap! It's cracked too! This crack is between the #4 and #6 cylinders and is a little different.

<img src="http://andy.speedgeeks.org/OtherImages/08.15.02-Allen_Heads/DSC00014_700.JPG" alt=" - " />

<img src="http://andy.speedgeeks.org/OtherImages/08.15.02-Allen_Heads/DSC00015_700.JPG" alt=" - " />

<img src="http://andy.speedgeeks.org/OtherImages/08.15.02-Allen_Heads/DSC00018_700.JPG" alt=" - " />

So, can anyone help us understand why this would happen? Keep in mind that the head gasket on the passenger side was fine. Now I'm starting to believe that the cracked head caused the blown head gasket. But I really can't understand how this could happen unless the heads were defective. BTW, the heads were hand ported by a local guy that does great work and then milled .035 at a local shop.

<small>[ August 19, 2002, 11:17 AM: Message edited by: Go FasTA ]</small>

 

Here are some additional pictures: http://andy.speedgeeks.org/OtherImag...2-Allen_Heads/

 

I'm no expert, but my guess is that the unshrouding for the valves and/or milling of the heads made those areas too thin. Looks like simply not enough meat there to hole the pressure. If those are water jackets running between the cylinders, that is why he was burning coolant.

 

When you say over heat what temps did you get to?

 

Andy, I think the car needed one of those A1 cams, then the heads would have been fine <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> ...j/k

Think hard, you'll remember what I'm talking about <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Josh

 

Was any nitrous used? Were the heads welded in that area, I noticed some pitting along the chamber wall that could have been due to poor gas shielding while welding. This worries me, I am building a set of 6.0L heads right now.

Paul J.

 

No nitrous was used on it and I didn't have the heads welded. However, I bought them from Valvegod and he said that some of his are welded but he doesn't know if mine specifically were. The temp gauge got to the first of the red and that's when I shut the car down. I don't remember what temp that is off hand.

Damian, I'm sure you are referring to the fact that the hammer cam was originally designed by Andy. Of course, I wouldn't want to use the torque specs he used for his cam <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Damian:
<strong>Andy, I think the car needed one of those A1 cams, then the heads would have been fine <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> ...j/k

Think hard, you'll remember what I'm talking about <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Josh</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> I remember exactly what you're talking about. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

Andy, it is time you stop doing motor work on cars. You seem to have crappy luck. Hence why I call my cam the "hammer cam" <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> , to keep your bad luck away from me. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

So Shaun said some of his heads are welded????? Did you purchase "never run" heads or heads that were run before?

Eric

 

Wow! That is the first I have seen anything like that!
I opened up a set of 98 chambers to 73cc. Before I did that I drilled between the valves on an old set of 98 5.7 heads to check for thickness.
It is solid deck between the valves.
The 6.0 heads must have a different coolant passage structure IMO.
Steve

 

Eric, I don't remember off hand if they were new or used but I'm pretty sure they were used. I bought them back in December but I can't find my receipt for them now to check on it.

 

Broke thru some water passages?

Keep us posted.

Valvegod does sell some re-welded stuff.

 

I'm sending my heads back tomorrow and I'll go from there.

 

from the pictures my conclusion is that they were repaired in the past at some point (best guess is gm scrapped them and he got the scrap now when gm scrapes heads they tend to make them unusable, IE a good chissel blow between cylinders works well and they sometimes even drill them.)
I would say they were repaired and resold (just a guess)the pit makes show they have been welded before IMO or the castings.Seeings as how I have never seen anyone else do this I would not think it was the castings.
Brent

<small>[ August 19, 2002, 10:04 PM: Message edited by: H82BBad ]</small>

 

Definately looks like they have been welded.Pits in cyls. and decks look looks like bad welds.May have caused blown gaskets but there is no water there to leak. it needs to be ground out rewelded and resurfaced.

 

is that a crack in the intake port in the second picture down?

the holes and nature of some of the cracks look like heat caused em.

 

Here's what was done to the heads. The chambers were cleaned up, and most work was done on the ports. I had a 3 angle valve job done and they were milled .035".

As for the line, it appears to be casting markings as they are on every port on both sides. The car did overheat as I was blowing out crap like crazy but was turned off as soon as it happened. I'm not sure if that would cause cracks or not.

 

Some GM take-off stuff is purposely cut with a cutting wheel so that folks won't reuse it. I know that Valvegod has had some LS6 heads with the head surface cut 1/8th deep between the central cylinders and he has rewelded some of them.

 

Thats a casting flaw, either sand or air caused a pocket beween those cylnders and de-shrouding them exposed the problem. I saw that problem here while porting a set of heads and caught it before they were installed.
Joe.

<small>[ August 22, 2002, 12:29 AM: Message edited by: JPR ]</small>

 

Hope you get the car back together soon Allen...

You buying Joe's old setup..?