2k Cobra

Two 2007 C6 Zs in our club had bad heads/guides.

Maybe they were practicing making bad heads in 2006 and 7...

Hib Halverson

.1 is a tenth of an inch
.001 is a thousandth of an inch
.0001 is a ten-thousandth of an inch but machinists sometimes use a vernacular term "tenths" to talk about it. For example, your guide clearance is .0025 which is 25-ten-thousandths of an inch or "two and five-tenths". This is always confusing to laypeople because they hear "tenths" and think the machinest is talking bout tenths of an inch rather than ten-thousandths of an inch.
.00001 is a hundred-thousandth of an inch.
.000001 is a millionth of an inch.

Keep in mind that GM engineers talk "metric" and they discuss stuff like stem-to-guide clearance in microns which are more properly "micrometers" or one-millionth of a meter. For example, the production tolerance for stem-to-guilde clearance on LS7 is 28-63 microns on the intakes and 25-68 microns on exhausts.

Hib Halverson

As of 24 March, the folks at Powertrain working on LS7 have contacted Katech and Lingenfelter Performance Engineering. They told me they would like to speak to West Coast Cylinder Heads and Texas Speed along with Service Techs at two dealerships, one in CA and the other in OH, who have nationwide reputations for working on Corvette engines.

I have asked GM Powertrain to supply an "executive summary" of their discussions about guides with all those companies and my assumption is they will give me that info once they conclude the process.

moose.b3

Hib, Do you think you will be allowed to post the "executive summary" here on CF?

shane p

sorry, shouldn't have used zeros because you ignore them

.1 is a tenth of an inch
.100 is one hundred thousandths because the last zero is three places to the right of the decimal which is in the thousandths spot like you pointed out.
You don't ignore the zeros because a lot of times if its three places to the right the decimal the tolerance is plus or minus five thousandths. if you like I could use
.101 that's one hundred and one thousandths, my whole point was some people don't know how small .0005 is and how difficult it can be to measure something ACCURITE to that tight of a tolerance especially using a dial indicator and mag base and moving a stem back and forth by hand that's a joke and for GM to ok it for sometime was a even bigger joke

Fabio-Z06

dmuellenberg

That is just your opinion, do you have any facts to back your statement up?

Again, the root cause(s) for the bad guides have not been determined. While the machining error may contribute to bad guides, there are obviously other factors involved that cause bad guides, even if the heads were machined correctly. All GM is stating is that there was a machining problem for some heads during a couple of years, that DOES NOT MEAN that bad guides can't happen in any year. I don't know why this is so hard for some people to understand.

dmuellenberg

In terms of actual number values, .1 is the same as .10 as .100 as .1000 etc., they all represent one tenth. If there are zeroes present, then that indicates the significance of the accuracy of the measurement. In other words .1 is only accurate to the tenths, while .10 is accurate to the hundreths, .100 is accurate to the thousandths and so forth.

Hib Halverson

If GM answers my question on-the-recored, I might.

It's more likely going to be rolled into another revision of LS7 article I have posted on another web site.

Hib Halverson

Well, as the saying goes "pewter99"..."You got nothin."

Since, in a later post, you refused an opportunity to cite the source of your "story" about the LS7's Ti intake valve and further stated you would not post to this thread again, thus depriving us of a discussion about the credibility of your information, I'm going to dispense the facts behind the Ti intake which are far from the myth above

What I say here is confirmed with multiple sources, three inside GM and a fourth at Del West. Some of this is research I completed three years ago and some is from a conversation I had earlier today with the Managing Director at Del West.

First off...
There never was a 475-hp development version of the LS7.

Three years ago, I examined this is issue thoroughly. Originally, during the late C5 period, the "next Z06 engine" was a 6.4L early development engine which made about 450-hp. It used a stainless steel intake. The 6.4 eventually was deemed inadequate after Bob Lutz (GM Vice Chairman), Tom Stephens (GM VP for Global Powertrain back in the early 00s) and Sam Winegarden the (Chief Engineer for the SBV8 in the early 00s) decided that the C6 Z06 must have 500-hp or more. Interestingly, the head developed for the six-four ended-up on the LS3 and the LS9, but...I digress.

Five hundred horsepower was the goal, never 475-hp. Now, the LS7 Team had a hard time making the last 20-25 hp but, by the time they were "plateaued" at 475-480-hp, the Ti intake had been designed for 500-hp and had already been in the program for well more than a year. The two key advances which finally got the engine past 500 were: 1) a change in the design of the block's crankcase to further reduce windage and improve bay-to-bay breathing (10-15-hp gain) and 2) the current LS7 exhaust manifold which was the final late change (gain 8-10-hp).

Your information about GM making Del West coming in on budget with a valve originally designed for 475-hp is inaccurate.

There never was a competition between Ferrea, which makes valves in Argentina, but sells in the US DBA "Ferrea Racing Components," and Del West for the LS7 intake. Ferrea was not considered back in the early 2000s when GM began looking for a Ti valve supplier after realizing a stainless steel intake light enough for 7000 rpm would not live at 500-hp. At the time, Del West had been making a Ti intake for the C5-R racing engines and their substantial success in that effort caught the attention of the LS7 development team and its valve engineer, Jim Hicks.

The LS7 Ti intake was always, as Del West told me, "single source only." Once Del West quoted GM a price to make a production Ti valve durable at the 500-hp level, the people at Del West thought that GM would "....laugh and go away." But they didn't. They signed a deal with Del West to make Ti valves at four-five times the cost of a premium SS intake valves.

The Ti valve for LS7 was a rare single source item for GM.
Del West did not come into the program until after the 6.4 was killed.
The power goal for LS7 and its Ti intake was always 500-hp and never 475.

But...for the sake of discussion, just forget these facts. Let's look at "pewter99"s story with some common sense.

Even if it there was a 475-hp "first design" LS7, do you guys really think even nasty GM is stupid enough to use a valve which could not be durable in an engine with 5% more horsepower?

Gimme a freakin' break! People are using those valves successfully at the 575-600 hp level in mod'ed engines, so that is a big clue that there's nothing "cheap" about the Ti intake. The idea that the valve was developed for 475-hp so it's a POS at the 500-hp level and that GM screwed us all by doing that is complete BS.

OK...here's my rant:
Ya know...GM has a problem with the LS7. They've not done to well fixing it so far but they seem to be more focused at this point. While some of you guys, like my pal "AZDANZ06", think I'm just happily boinking GM waiting for my free Vette, what I'm trying to do is cut though some of the crap and get people some facts.

Posting fairy tales like this fabrication about the titanium intake valve really doesn't move the ball forward in this discussion, but....I'll admit: if someone is just pissed-off and wants to post a tasty, anti-GM rant, regardless if it's true or not; it makes great red meat for haters.

propain

Thank you for this side of the story. Good read.

SA WHN

New member here from central California. I purchased a new to me 2010 10,000 mile ZO 6 a couple of weeks ago and have been reading the ZO 6 threads. Sounds like I bought a car with faulty heads and an engine that could blow up at any time. Wrong car for me so back to the drawing board. I like to drive them like I stole em not parked in a garage for fear the thing will explode leaving my drive way. Wow, I was under the impression these were good cars. And I sold my 900 mile GT 500 for this?

'06 Quicksilver Z06

Thanks Hib for the info and clarification.

Apparently the story that you are debunking has existed in some form or another for some time, as I heard parts of it from the guy who I sold my factory heads to back nearly 3 yrs ago.

Like many here, I appreciate your efforts and encourage you to keep up the good work.

2k Cobra

How many auto forums are having this discussion?

GM messed up and didn't stand behind their mistake. Doesn't matter what date, time period or the phase of the moon, They screwed up. If they stood behind the problem we wouldn't be having this discussion.

VetteVinnie

It has indeed. And it was told to me by a credible source who remain unnamed as well. There's often a big difference in a story when discussing things "off the record" and when discussing things with a journalist.

propain

Attempting to debunk. Don't get all carried away again Quick. I know you are star struck quite easily.

Its another side of the story. Neither proved or disproved.

'06 Quicksilver Z06

Whatever.

It's more than you and the rest of the "wiggle crew" ever did toward's "attempting to debunk" that story.

Say what????

WTF good is a "test" which is only "useful" at the point when your valves are so loose, that your engine is at death's door?

So if you pull your valve covers and you "can't" wiggle your valves by hand, then you're alright????

Advocating that $*** when direct and accurate measurement is available for a minimal up charge , is ridiculous.

Symptoms of acute carbon monoxide poisoning or radiation sickness will tell you if you have been "grossly" exposed to either.

The idea of any preventive oriented "test" is to let one know before that point is reached.

But then again, people like yourself, are easily impressed with "tests", no matter their practical value or lack thereof.

Exactly.

JoesC5

What do you consider is a "minimal upcharge"(over a "wiggle test") to remove and replace the heads along with a full disassembly of both heads and measuring each valve and it's corresponding guide, and then reassemble the heads and install new head gaskets and new head bolts along with an oil change?

Isn't GM the original "wiggle Crew"(and not any CF members)as they said that was the "test" that their dealers should perform to evaluate the valve guides?

JeffInDFW

I'm realizing this has become a lot like discussing religion. I wish someone would ban the 4 religious zealots posting in this thread so we could have a better chance at solving this mystery.

Hib, this is the closest we have come so far to getting a solution on this. At least GM is finally looking at it. I'm livid that GM has ignored this for so long, and believe it is GMs own fault that there are so many incorrect theories. GM left the Corvette community to figure this out on their own for 5 years while engines were blowing left and right. However, I'm not closed minded. The detailed explanation on how the "Wiggle Test" is inaccurate enough that it gives false positives makes sense. I also agree with posters who point out that if a guide is horribly out of spec the "Wiggle Test" is still of value. I also believe GM is being honest when they say they know that there was one specific episode of bad machine work around 2009. THIS DOES NOT MEAN THIS IS THE ONLY TIME THERE WAS EVER ANY BAD MACHINE WORK. There could have been other times when there were other problems. There could be many other things happening that are causing the head to break off the exhaust valves. Those are other issues that must be investigated.

As for the Del West valves......I just got off jury duty today, so maybe I'm still in that mindset. But looking at the two different stories and sources, I have to make a judgement call on which one I think is most likely correct. I do not know anyone involved. But, I do know there is not a chance in hell that GM or any supplier cuts tolerances so close that a valve that is spec'd at 475hp would fail at 500hp. There are tons of modified cars making a lot more than 600hp with the stock valve that are not failing. In this case, I would find for Hibs version of the story.

So, I'm a sucker that believes anything GM says. Not at all. As I said, I blame them for whatever IS causing the LS7 to drop valves at a higher rate than any other engine I am aware of. I blame them for ignoring this problem for so long that it has become the mess it has become. I blame them for forcing Corvette's CUSTOMERS to try to figure out the cause of this problem. I blame them for the huge cost so many Corvette customers have had to bear to repair damage from dropped valves, AND for the cost they have incurred trying their best to prevent a valve drop problem and doing so with ZERO information from GM itself. The lack of trust so many here have toward GM (including me) was CAUSED by GM.

Now, I want to know what the next steps are. We have been told the wiggle test is not accurate. We have gotten clarification on what was wrong with that specific batch of heads around 2009. Has anyone raised the alarm about concentricity with them? Do they know to look at this? What about all the other theories the Corvette community has come up with as to what causes the valves to drop in the LS7?

At the end of the day, GM must answer the issue of why the LS7 drops valves more than any other engine I am aware of.

JoesC5

I agree with just about everything you have said.

I guess that I should be elated that I am fortunate to own a 2009 and spent $4300 for new heads because GM looked the other way.

I also was one of the fortunate GM customers that purchased a new 1970 Vega with it's oil burning engine(and GM also looked the other way). I was elated about that also.

There won't be a third time for GM to look the other way while I have to spend additional money to pay for their mistakes(there is a word more fitting, but it keeps getting deleted when I type it in). I'm done with GM. And I am really, truly elated about that(no sarcasm). It's not just the Corvette I'm not buying new again, but the other cars that are in my garage that will need replacing in the future. $100,000 for a new C7 Z06, that's a laugh. Is GM going to look the other way if it has a problem? Not with my money, they won't.