ATC399

Yeah he could...But that would not be the norm for C6Z section...Good luck OP....you are buying a used mass produced street car.

MTPZ06

There are three buckets to fall in here:
1- Those who are verified to have an issue (by competent shop, catastrophic failure, etc.)
2- Those who are verified to have no issue (through proper inspection)
3- Those who have absolutely no clue as to whether their car has an issue.

I unfortunately fall into that first bucket...but thankfully I caught it and corrected it because I was proactive and paid attention to all of the evidence displayed here.

The vast majority of owners sadly fall into that last bucket. The majority of C6Z owners aren't on the internet researching this topic, so as they say...ignorance is bliss. But if you are an owner that is informed on the subject matter of premature valve guide wear in the LS7 (which is a very real issue); and you choose to ignore it...well, then ultimately that's your choice. Its your car and do as you may...but its just beyond me why anyone out of warranty would not be willing to at least do something as simple as a wiggle test just to see if something needs a closer look. That just sounds like ignorance minus the bliss part.

LFZ

So fortunate to have all these experts in one thread. I'm not going to start my LS7 ever again....OP I suggest you do the same.

redbird555

No need to be a smartass, no one is claiming to be an expert. Personally I have 3 friends with z's none have had issues even with high mileage. I think the problem is over inflated. I checked my heads at 17k and they had some movement so I did the heads.

Gary '09 C6

Even the new replacement GM heads should be measured before installation, as we have seen at least two reports
here on the CF regarding the same being partially out-of-tolerance.

Unreal

If you want to do 10-12 track days a year, heads are just one of the things to be addressed. I would contact Katech or one of the track places and get a nice list of upgrades to do.

American Heritage

Regarding core charges: We do not charge a core charge just a fully refundable core deposit (if using our core heads).
Once we receive your core heads we credit you back the core deposit the same day.

http://www.americanheritageperformance.com/

fueledpassion

Why the derogatory comment? SMH.

This thread was going in a silly direction talking about whether or not you can rev the car past 'X' rpm. Everything I posted here is everything that this forum and the corvette action center have discovered or made note of as a contributing factor to the cylinder head issues.

The point is, we're not sure which is exactly the cause of broken valves, but we know that the guides, valves and rockers all have to agree with each other on geometry of the parts in order for any of it to work properly...

It is a high performance engine...a VERY high performance street engine. Expect shorter life on things especially when racing. No one says "don't start the car" or "don't drive it". It's just a risk you MUST take every day in this car if you wish to drive it.

-------------------------------------------


Also, the whole "engine is noisy" thing is something to NOT take seriously unless there is a loud and obvious ticking sound of metal-to-metal contact. Otherwise, when you "fix" the heads, often times the valvetrain can get louder if the cam is aggressive and the pushrods aren't perfectly matched...

Quicker10u

If you genuinely think that RPM (mechanical Over-rev) has not played a huge part in the issue with dropped valves, you might want to re-think that...Float a valve with a problematic valve guide-a large part of the failures. Some who own these cars are absolutely not qualified to operate them. Then they claim that the car dropped a valve while idling in the garage-after the rev limiter-bouncing burnout, or missed shift at the top of 3 while racing in "Mexico" that they fail to mention. Hence the problem gets magnified.

fueledpassion

I'm going to be direct - I don't think that and no where in my post did I insinuate such a thing. I'm talking about people being afraid to drive their car to WOT and shifting within the normal operating RPM's, which is defined as something below the mfg rev limit. I always stop at 6500 because rarely do I ever need to rev past that to have fun, win races, etc..granted, I do 100% street driving atm. The thread was going in a direction of placing severe limitations on what the stock LS7 can do safely. Those valves/guides are gonna wear out regardless of revving to 7-7.5K repeated times and refusing to enjoy the car's power is not going to help the issue all that much. I'm certain many have mis-shifted and shifted late and caused damage over time that led to a valve dropping but I'm also sure that the guides were known to be non-concentric and the flat tappet designed rockers are susceptible to causing side-loading/valve stem wear and it doesn't take 7K rpms to do that...It just takes a running motor. That is my point.


Have an internet beer with me and let's forget the topic.

Quicker10u

No worries man! I wasn't trying to be jerk-ish about it. I just feel that there seems to be no real sense of responsibility from a lot of the owners that feel it's all GM's fault. They built a engine that really pushes the envelope, and they knew that. Does it excuse their manufacturing flaws and material choices-no, but If you act like a Yabo and don't respect that the car is so close to it's mechanical limits, you're gonna have a bad day! I am going to be proactive about it and swap the heads, keep my original heads and have those done down the road (after a good measure on the guides and see how out of spec they are after 11k). I've been tracking cars for a long time and the problem has been well known.


Cheers and beers It's Friday!


Ken

olddragger

by the way OP--once the heads are addressed, fixed if needed---this platform and engine are pretty stout. I don't think you will be disappointed..
Keep the temps in check, run good gas, buy lots of tires and brakes and drive this monster.
You will be very tempted to start modifying---maybe?

starchedup

OP... Keep in mind once you start modifying you will be forever modifying. I don't think you'll ever be happy with your performance because you'll see there's some new thing/widget that'll give you more power. I just caution you to be careful with what you modify because you will forever be spending money. And my final recommendation would be to not go into the bottom end of the motor. Leave it stock.

If #7 piston hadn't blown and cracked the sleeve I never would've re-sleevesd my motor and started this TREK.

FYI I am on my third short block if you count the original

fueledpassion

And to add to that, get a DD car that is the exact opposite the Z in every way possible. High off the ground, sluggish, a turd in terms of power, short-legged gears, etc. I'm thinking a lifted 4-banger Ford Ranger will do w/ large tires & a tall order of gears.

It helps enjoy the Z all the more when there is a strong contrast b/w the two and that will help you with "delayed gratification" when it comes to modding your car for MOAR POWER

starchedup

While I am sure that was meant as total sarcasm, you have a point. I would never daily drive my Z. My daily driver is a five cylinder four-door sedan. All the mods I've done we're only done because it's my sunny weekend toy/track car

Livefast1098

Already own this money pit...
<br >

Livefast1098

Bases covered!
"MOAR POWER" you say? Yah! That thing's got a Hemi!!
<br >

Lawdogg

LS7s often have guides that are way out of spec. They do not need a mechanical over rev to break the two piece exhaust valve.

REDZED2

What no one has touched on or noticed.. like me the OP is Canadian... so if doing the usual.. with port work.. hollow ex. Valves mill.. the regular rebuild with shipping ur around 1800-1900... then if temp. Core charge is applied with exchange at .75 cents and our taxes ..we Canadians sit at around $4600 cdn!!!!! Even getting back the core charge a week later ..

..u still have to slap that kind of coin for the non rich guys that dont want or cant afford down time... rediculous!! Companies should not charge a core charge on the heads unless returned within a reasonable time frame. Not right at time of purchase!! Some Vendors think everyone has 100k plus in their accounts and throw around prices like ur buying a pair of jeans... yeah right....

bjmsam

That explanation is supported by a growing body of empirical evidence collected over the past several years:

An evaluation enables informed decisions:

My heads are presumably from the good batch considering all valve-to-guide clearances measured within service limits at 62k miles, so having them checked avoided both 1) the cost of unnecessary replacement and 2) the risk of ending up with random core replacements from the bad batch (when the time comes, I will have mine refreshed instead).