LS7 Failures in the Z/28's How Many?

[MX621]

Originally Posted by BJJKRIS

Sent my heads in to AHP as a core so I wouldn’t have my car down for too long. Just got wiggle test results back on mine.

Completely stock other than kooks long tubes. Stock cam.

“More than a few guides at .015.”

Lucky my engine didn’t eat itself on my way down to Miami before I pulled the heads.

So if there was any question on whether or not the LS7 heads were fixed on the z/28...


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Quick research found the gm service limit spec is .0037”
So .015 is crazy loose!! Good catch/save!

[BJJKRIS]

Originally Posted by MX621

So I’m assuming .015 guide/valve clearance is out of spec?

Anything over .008 is considered out of spec. Pulled mine right at 20xxx miles. I’m at 23000 now with new heads (been driving it like I stole it too) with no issues other than its insatiable hunger for spark plug wires.

I hope to have a detailed printout for each guide with measurements soon. I will post it here once received.


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[BJJKRIS]

Full printout of results.

1 int: .016"
1exh: .006"
3 int: .018"
3exh: .006"
5 int: .013"
5exh: .006"
7 int: .011"
7exh: .006"

2 int: .009"
2exh: .006"
4 int: .013"
4exh: .006"
6 int: .009"
6exh: .006"
8 int: .010"
8exh: .006"

And there you have it. Don’t sleep on the LS7 in the Z/28.


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[2SSRS@Gen5diy]

Originally Posted by BJJKRIS

Sent my heads in to AHP as a core so I wouldn’t have my car down for too long. Just got wiggle test results back on mine.

Completely stock other than kooks long tubes. Stock cam.

“More than a few guides at .015.”

Lucky my engine didn’t eat itself on my way down to Miami before I pulled the heads.

So if there was any question on whether or not the LS7 heads were fixed on the z/28...


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Who is AHP?

[j o n]

Originally Posted by 2SSRS@Gen5diy

Who is AHP?

https://www.americanheritageperformance.com/

[Biergut]

Okay... let's assume this is an issue in all engines... so how would one go about getting this resolved BEFORE the warranty ends and BEFORE one's engines expires? So I use it in a very severe track environment, 6800-6900 RPM is not unusual, how do I get Chevy to look at this issue if we're seeing no signs of trouble? (14k miles currently) Or am I just SOL if there is nothing manifesting?

[Katech_Zach]

Originally Posted by Biergut

Okay... let's assume this is an issue in all engines... so how would one go about getting this resolved BEFORE the warranty ends and BEFORE one's engines expires? So I use it in a very severe track environment, 6800-6900 RPM is not unusual, how do I get Chevy to look at this issue if we're seeing no signs of trouble? (14k miles currently) Or am I just SOL if there is nothing manifesting?

Chevrolet typically refused warranty claims on this issue unfortunately. Your best bet is bringing this up now with the dealership and starting a case prior to the warranty expiring. That way, you have some ground to stand on by showing that you were aware of this issue long before the warranty was gone.

[BJJKRIS]

Originally Posted by Biergut

Okay... let's assume this is an issue in all engines... so how would one go about getting this resolved BEFORE the warranty ends and BEFORE one's engines expires? So I use it in a very severe track environment, 6800-6900 RPM is not unusual, how do I get Chevy to look at this issue if we're seeing no signs of trouble? (14k miles currently) Or am I just SOL if there is nothing manifesting?

Some have had better luck than other regarding having a warranty claim turn out successful. There are recorded cases of complete engine failures getting paid for (better hope your car is stock and with no tune).

You could always have your heads removed and then check for valveguide play. If there’re our if spec I’m not sure how you’d bring that up as far as a warranty case goes. I’m sure someone here could answer that.

For now your best bet is to take care of the issue now before the warranty runs out. You don’t even have to go super baller with the ms90 guides and what not.


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[Gbland60]

Even if GM would cover it, how would they? By taking your heads off and slapping on another set of LS7 heads off the shelf? Or would they actually take your heads to a reputable shop and have them do the job correctly. Well if they did that wouldn't they be admitting fault and the C6 ZO6 Corvette forum would blow up

[MrRaZ28]

Originally Posted by Gbland60

Even if GM would cover it, how would they? By taking your heads off and slapping on another set of LS7 heads off the shelf? Or would they actually take your heads to a reputable shop and have them do the job correctly. Well if they did that wouldn't they be admitting fault and the C6 ZO6 Corvette forum would blow up

From what I've seen, they replace with off the shelf heads. And there are reported instances where the replacements were even more out of spec than the ones taken off.

Edit: That's what prompted me to get them replaced and get the rest done all at once. The scenario of maybe warranty/maybe not warranty - maybe good/maybe not good - $3k/$7k - blown engine/replacement with possibility of exact same problem/me having to chuck $17k for a crate engine - .... all boils down to me being effed out of money somewhere. The stress was awful. Regardless of opinions, fact of the matter is the geometry for the valve train was just not accounted for properly in their design and it needs to be addressed at some point. ESPECIALLY if the machining issues have persisted. Speaking from a 12 out of 16 rockers being damaged standpoint. Valve guides at minimum need to be longer.

[Gbland60]

Roger on the stress factor. Agree with guides being .250 longer. I'll probably never see 7k rpm on mine. That's pretty high for my taste on a 427 pushrod. I'm putting back 4k for both heads to be rebuilt bullet proof once and for all. Im tired of cold starts and listening carefully for any out of the ordinary noises and coming home after a drive popping the hood grabbimg the stethoscope and probing around afterwards. Taking valvecovers off every 5k miles checking springs and rockers. Crap gets old man. Figured 4k or alil more with my labor doing the work i should start sleeping all night again and maybe my bowels will get back regular again ! Sarcasm of course. Kinda on the fence with exhaust valve choice since like i said I'll probably never see 7k rpms but a few times (maybe)

[Biergut]

Originally Posted by Gbland60

Even if GM would cover it, how would they? By taking your heads off and slapping on another set of LS7 heads off the shelf? Or would they actually take your heads to a reputable shop and have them do the job correctly. Well if they did that wouldn't they be admitting fault and the C6 ZO6 Corvette forum would blow up

Right. In speaking to a friend last night the catch-22 was discussed. Tough call -- take chance until the warranty runs out? Do it now? If something "else" were to go wrong and the engine failed I can gaurantee Chevy would not do a thing if there was any modification whatsover. I guess in the meantime I should stop running it up to 7000 rpm on track. I really don't stress too much as it's still under warranty, but I hear you all as soon as it's out... plus these threads don't help much.

[hjdca]

Originally Posted by BJJKRIS

Full printout of results.

1 int: .016"
1exh: .006"
3 int: .018"
3exh: .006"
5 int: .013"
5exh: .006"
7 int: .011"
7exh: .006"

2 int: .009"
2exh: .006"
4 int: .013"
4exh: .006"
6 int: .009"
6exh: .006"
8 int: .010"
8exh: .006"

And there you have it. Don’t sleep on the LS7 in the Z/28.


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Is there a reason the intake guides are mostly the ones "out of spec." ? Could it be that they were assembled that way and it was not "wear" that caused the issue ? The exhaust guide specs seem to show zero wear.

[BJJKRIS]

Originally Posted by hjdca

Is there a reason the intake guides are mostly the ones "out of spec." ? Could it be that they were assembled that way and it was not "wear" that caused the issue ? The exhaust guide specs seem to show zero wear.

There’s more than a few recorded cases of intake guides being out of spec as well. But in this case it could be a typo. I thought the same thing as well.


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