Random84

I doubt anyone here really cares about the GM statement all that much for a variety of reasons - if anything, Katech is spot on (again) and points out... on page 2?... that their observation of valve guide issues is both intake and exhaust, and has recently been noted on `07 and `08 cars (as we all know). Guides. Not valves.

So we're all in agreement then?

'06 Quicksilver Z06

Random, like people have said, this one has petered out.

Stay on your soapbox if you wish, but this one is over, the crowd is leaving.

z0sicktanner

then why was it other ppl finding the problem before katech and posting it? katech said it was a small % when others like myself took the time to really post things as I seen them. they said guide wear wouldn't cause valve failure. they also said it was the piston bad driving .then they post a guide spec sheet with intake guides worn over.0100 and said untill we seen this. well then. how long have ppl been posting those same numbers with the exhaust valve and they wasn't worried with the Hollow valve? but they sure posted some spec on a solid ti valve...and said this will cause failure. well No sh**

propain

I would agree and its a good thread title already.

'06 Quicksilver Z06

I feel bad for that poor guy over there who just lost his motor.

Thing that bothers me is that didn't have to happen. No sir. That didn't have to happen.

It's guys like that, who I'm trying to reach and if I step on some toes doing it, well, it would have been worth the $15-$17K this guy is likely out now.

No doubt in my mind had the "Steelers", as I guess we are referred to now, had reached him a month ago, that car would be running today.

Oh well. At least now, he will have a chance to make up his mind what heads and what valves he is going to use in his next motor.

You've been away for awhile.

But I can tell you this. It is extremely rare, for someone in here who has dropped one of the stock exhaust valves, to go back with stock exhaust valves in their next build if it is not being covered under warranty. Even in the midst of all the talk that the stock valves are OK.

In fact, I don't think that I have ever seen it happen.

propain

Yes, people need to be made aware with solid evidence and a clear path to a fix. If this can be presented in a sticky on this forum in a clear manner without the drama I believe people will take it seriously.

We all know GM isn't going to do crap about this.

Rock36

Maybe I am misunderstanding your position, but are you denying that the preponderance of valve guide wear is typically on the exhaust side? Even when intake guide wear is present, it is usually markedly worse on the exhaust side, particularly at the bottom reading of the exhaust guide.

Surely you have seen this thread:

http://forums.corvetteforum.com/c6-z...ster-list.html

DON T.

Well Said...

hoefi

What makes you so sure that the intake guide wear and the exhaust guide wear share the same cause? Could it be that the coating on one batch of intake valves were not smooth enough and caused "some" intake guides to wear out prematurely?

Also, what makes us so sure that GM is not telling the truth about the machining error for some of the model years affected? Maybe the machining error is "in addition" to the "original" problem. If there are in fact two problems, they are not mutually exclusive. The end result is the same, with the machining error introducing guide wear in the intake side of the head also. If one (like yourself) made a prior assumption that there could only be one cause to what we are seeing, then your whole analysis could lead you down a completely different path.

I don't know how detail you went into reading my past posts, or whether you read "every" posts I made on the subject. I stated way back that the problem originated with GM's decision on using a 2-valve head. I also stated in one of my earlier posts that one of the tell-tale signs of having a heat issue is the overly rich air-fuel ratio GM uses in this engine. Are we so naive to think that engineers in GM don't know how to tune engines? If they can lean it out and claim another 25 horsepower, why wouldn't they do it? The biggest effect of a rich mix is to lower combustion heat. To say the LS7 is pig rich is an understatement. Go to any track days and look at the tail pipes of any Zs. Then go take a look at the Porsches and BMWs. So, the question is why does GM want to contain combustion heat? Which engine internal part is the first to fail if such heat is not contained? There are two great candidates, the piston and the exhaust valve. Katech has mentioned multi times that they see more piston failed than dropped valves. Well, we certainly don't have threads after threads reporting failed pistons, do we? The fact remains, out in the field, there are more valve failures than piston failures. Does that point to a heat issue? You decide, I already have my answer. One problem with matching the heat theory with field reports is the difference in how we interpret "hard driving". Some think that track miles automatically mean harder driving than street miles. My 35+ years of motorsport involvement showed me otherwise. Some (including some instructors) actually don't drive that hard at the track. Some (like Jimman) would like to tell you he tracks and that he drives as hard as anyone else. Then you find out at 90,000 mile, he is still on his original brake rotors. I always said you can tell how hard somone drives by the color of his brake calipers. This is the internet, and you can't believe everything you read.

In regards to a "proper" repair and its justification relative to the establishment of "root cause", I think it's a waste of time to argue about it. I said in an earlier post many years ago that the only true solution to this problem is a multi valve head, anything else is just a band-aid solution. OE valve or solid SS, pay your money and take your chances, I don't really care. I find it funny to hear people who talk about how heavy the solid SS valves are and how it will affect revs, blah, blah, blah.... I come from the world of imports and the two Corvettes I have ever owned are the only two V8 engines I have ever owned. Talk about heavy valves, even the LS7 OE intake valve is WAY too heavy if it is compared to all the "little" valves out there. "Heavy" is a relative term, if we can put a man on the moon 40 years ago, we can certainly run a solid SS valve to 7,000 in the LS7. And I am confident that the upcoming Katech undertaking will confirm that it can be achieved. As for people who worry (or claim) that heavier valves would slow down the engine acceleration rate, trust me, a set of 20" wheels have a lot more inertia and would kill your acceleration rate way before the little valves do. If you worry about the extra weight of the SS valve, you shouldn't really be using the OE 19" wheels in the rear.

z0sicktanner

great post. if not the best on this thread

FrankTank

This is what swayed my thinking, and to believe the problem was more widespread than I thought. I still remember reading Charlie from RPM's thread and some of the data he was reporting , that was the turning point for me at least.

Several shops across the country, competitors but all seeing Guide Wear and dropped exhaust valves, and all pretty much recommending the same fix, and in some cases many shops using the same vendor WCCH

I said way back when that I would admit I was wrong about how widespread the problem was, and I've done that

No offense to hoefi, or chad (Z06tanner) but back then, most of us did not know you from Adam, you were just 2 people waving a red flag about this problem, on a public forum... other than your arguements and *some* data you offered of a couple of sets of heads and motors ...it's hard to not Believe what Katech says, with their reputation and knowledge, and years of experience. Again remember this is the internet..I could say I'm an astronaut and photochop pictures perfectly, make up my credentials or whatever... just leaves to much to suspect.

Now fast fwd to current day we at least have more examples and data to show you guys were correct. So you guys took a lot of heat (no pun lol) and thrashing for making noise about the problem upfront, now there are quite a few of us that will eat a tad of crow.

I still believe Katech's statement about what the actual problem is, and I do believe part of GM's statment... but obviously I don't believe the MY they stated were effected as we've clearly seen Guide Wear and dropped Exhaust valves across the whole span of the Z06 run.

Mark2009

I think it is likely given the similarity in the pattern of wear.

If there was no mechanical misalignment (machining) and no side loading on the stem (geometry) then I would expect a rough stem surface alone to produce symmetrical wear the length of the guide bore; not the tapered wear we are seeing.
That is two truths:
1. Machining error.
2. MY affected.
The latter could be false without affecting the veracity of the former.

I think that any hypothesis that a combination of events lead to the same pattern of guide wear in both intake and exhaust guides with a different reason for the wear in each side is a pretty far stretch.... compared to the theory that a well-machined head using OEM components would exhibit no accelerated guide wear on either side.

That doesn't read too well, so I'm saying it is most likely that the same issue is causing at least the initial wear on each side (intake and exhaust), which would exonerate the OEM exhaust valve as being the root cause (but would not exonerate the OEM guide, depending on the claim against it).

I did read that and would not disagree with that more valves would be better, but I see no evidence or reasonable explanation that supports the large-valve-is-the-root-cause hypothesis. Yes, it has to sink more heat. Is that causing the problem? Unknown.

Long term reliability. Detonation. The latter is probably one reason why they used the sodium valve to start with, which does not bode well for those replacing it with a 'less-conductive' valve.

I permanently blued new rotors on my C4 ZR-1 the first time I tracked it. Does that make my arguments here more valid? Or since I made that claim on the internet, does that mean it is not true?
.

Michael_D

When the engine is in closed loop (which is most of the time), the O2's report an over / under stoic voltage to the ECM which then trims fuel to pull combustion to stoichiometric AFR of 14.7/1 for gasoline. When the ECM goes into open loop, the AFR follows the commanded PE (power enrichment) EQ ratio, which does in fact enrichen the FA mixture. However, there are a few parameters that need to be met before PE is enabled. For the OE tune: Throttle position threshold verse RPM, MAP kPa, Map Hyst, Enable rpm, RPM Hyst and PE delay. PE works similar to four barrels and power valves. So.....to say the LS7 is pig rich isn't really telling the whole story. It's only pig rich when parameters are met.

I find it funny that a PE would make fun of people who give serious consideration to valve train weight and mass. This is 7000+ rpm 7 ltr V8 push rod valve actuated, cross plane crank IC engine, not a 5 ltr V12 flat plane crank, over head cammed IC engine. TOTALLY different animal with completely different design criteria.

sky1

If your choice is to runa stainless exhaust valve in the LS7 I would not worry about that at all.I hear alot of arguments about the weight and all and it is arguing over nothing.

I ran a 2.40 intake and 1.90 exhaust valve in a race motor that saw 7500+ rpm and they where both SS valves.I should of run a Ti Intake but I didn't.I never broke a valve and I had like 250lbs of seat and 750lbs of open pressure,and all my valves where pro flow valves (narrowed stem by head) from Ferrea.

When I have my LS7 gone thru down the road I will put either a SS or Ti exhaust valve and not look back.

On a different note I owned an 06 Z06 and like many others it had ALOT of valve train noise,but my 2012 Z06 has about as quiet a valve train as you could get,I mean you hear nothing coming from the valve covers and I even have the plastic covers off.

Mark2009

That you may not see it or understand it, or disagree with it, does not mean it is nothing. Denial of physics is not a wise argument.

However, as is common the argument of others has been mischaracterized by those who are unable to validate their claims. That the heavy solid valve can be made to work is not in dispute; the reason for using it is.

Random84

You are.

Mark2009

Ah yes, I forgot to comment on the heat load theory. Since we are seeing garage queens and other low-mile non-tracked cars showing up with worn guides, that tends to disprove the heat load theory.

Since we are seeing relatively low-mile tracked cars/engines, like forum member Dirty Howie's, showing up with intake guides worn pretty much equally as exhaust guides (.005+), that also tends to disprove the heat load theory (since the wear is equal on the cooler intake valve guide).

Then I would suggest not arguing about it.

Since the root cause has not been determined no solution can be dismissed. As another noted, I find your line of reasoning unusual for an engineer.

Another comment that I find unusual; that weight affects valvetrain performance is unarguable.

We could have put a fat (heavy) man on the moon, but we didn't. Of course, no one is arguing that we couldn't have.... but as long as the skinny man had no measurable defect, there was clearly no need to replace him with a fat man and have to beef up all the supporting components.

Plus, can you even imagine the effects of cabin decompression on a Twinkie?

jimman

That was the second set of brakes at 90K, currently on the forth. Also reference the rev up theory it's more like what you do to the internal resonance of the moving valve train with spring weight differences to compensate for the heavier valve and the long term reliability of the engine. Do you really think that some of the race teams will operate at high sustained rpm’s with an unbalanced system, I think not.