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#7 has no compression....

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Old Nov 4, 2008 | 05:36 PM
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Default #7 has no compression....

and the plug looks like this!




I haven't torn it apart yet but I have a pretty good idea what it looks like with small flecks of alum. on the plug. So now what do I do next? I have a nice bunch of parts. What would you do with my parts? What shortblock would you apply them towards? If I go too big, my cam, heads and headers will soon be undersized. This one was supposed to have 27k miles on it out of a '04 GTO. And it looked it too..... BTW, NA all the way!
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Old Nov 4, 2008 | 05:57 PM
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I'm guessing the ringland came apart....
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Old Nov 4, 2008 | 06:27 PM
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What causes this? I haven't overheated it. Did it go lean? I did have some oil mist from the PCV. Did the oil cause it (detonation)?
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Old Nov 4, 2008 | 06:43 PM
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I can't see the picture at work because of picture filters. Usually, no compression = ring failure, ring land, or destroyed pistons. The usual cause of this is detonation.
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Old Nov 4, 2008 | 07:06 PM
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Do a leak down as your first step.

Did you drop the plug or was it closed like that?
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Old Nov 4, 2008 | 08:52 PM
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Originally Posted by DaddySS
Do a leak down as your first step.

Did you drop the plug or was it closed like that?
LOL, a guy at work said, "you dropped that plug, right?" I showed him the nick on it. It has been hit by something... ie, chunk of ring or piston. I'm positive with what I've seen that I will hear air come whistling out of the dipstick tube. I poured some oil in the combustion chamber and came up with 25psi vs the Opsi I got with no oil.
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Old Nov 4, 2008 | 08:56 PM
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Originally Posted by frito1
LOL, a guy at work said, "you dropped that plug, right?" I showed him the nick on it. It has been hit by something... ie, chunk of ring or piston. I'm positive with what I've seen that I will hear air come whistling out of the dipstick tube. I poured some oil in the combustion chamber and came up with 25psi vs the Opsi I got with no oil.
That's a fair indication that you have ring problems and while I don't see how a bent valve would do what you're seeing, I would want a little more proof before I decided - take the heads off or drop the engine.
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Old Nov 4, 2008 | 09:57 PM
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Originally Posted by DaddySS
..... or drop the engine.
Yeah, I will drop the engine and pull it apart on a stand before I start ordering anything. I guess I should have added that the rest of the plugs looked like new so the excessive fouling would have been proof I didn't drop it after I pulled it out.
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Old Nov 5, 2008 | 08:38 PM
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Does the stock LS1 PCV system create enough oil mist to detonate and cause piston failure? I'm trying to make sense of this so it doesn't happen again. I will have a catch can next time but not sure that is what caused this....

The #7 intake runner is dry. The rest were plenty oily of course. So that means #7 hasn't been sucking for some time. I really think this piston has been dead for a long time.

Last edited by frito1; Nov 5, 2008 at 08:44 PM.
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