LS7 valve guide news.
 

Last week I was in Michigan for a day of meetings with various engineers at the General Motors Powertrain Division. Two of the meetings were about GM's two new premium V6 engines, the LGW and the LGX. The third concerned the LS7 valve guide wear problem.

Present for the LS7 meeting on the afternoon of 24 March at GM Powertrain Headquarters in Pontiac, were: Jordan Lee, Chief Engineer and Program Manger for the Small-Block V8, John Rydzewski, Assistant Chief Engineer for Small-Block V8 Passenger Car Engines, Chris Cogan, Cylinder Head Design Release Engineer for the LT1, LT4 and LS7 and Yoon Lee, LS7 Design System Engineer. Also present was Tom Read, Director of Communications for GM Powertrain. In attendance for part of this meeting were representatives from GMPT's Inspection Department, from Zeiss U.S. and the GM entity which complies service information.

This meeting included a visit to the Inspection Department at GM Powertrain HQ where I observed a Coordinate Measuring Machine (CMM) session with the passenger side cylinder head which was removed from my engine in July of 2014 during a warranty replacement. A CMM captures measurements used to create an extremely precise, three-dimensional, digital model of an object, such as an LS7 head. The GMPT Inspection Department uses Zeiss "Prismo Navigator" CMMs which are accurate to two microns over a distance of 300-mm ( .00008-in over one foot).

What I learned from LS7 Team at Powertrain will be incorporated into revisions to my series of LS7 articles which are posted on another web site. These revisions will take some time to produce. There is no posting date for them at this time.

There are some open issues remaining after this meeting and they will be explored via a follow-up exchange of emails I will be having with Tom Read and the LS7 Team in the next week or so.

At this point, I can reveal some news items which came out of that meeting. I'll cover them briefly, here, and will expand upon them, later, in my revisions to the LS7 article series.

1) "Wiggle Testing" at best is inaccurate and in many cases is completely unreliable. Observing one of my heads being measured by one of GM's Zeiss CMMs proved to me conclusively that even the complicated and careful procedure I covered in my Wiggle Test article produces data which is inaccurate and inconsistent such that, unless the clearance measured is significantly greater than the Service Limit of .0037-in., the measurements are useless for determining if a head needs repair or replacement due to valve guide wear.

2) It is possible that heads which had Wiggle Test results of more than .0024 (intake) or .0026 (exhaust) but less than .007-in. stem-to-guide clearances had actual clearances below GM's .0037-in Service Limit, regardless of how the Wiggle Test was done. That possibility becomes greater as Wiggle Test measurements get closer to .0037-in. Once they approach .005-in., guides are likely in spec even though they Wiggle Test as bad.

3) Some, but not all, heads which failed "Wiggle Tests" and were repaired or replaced, either under warranty or not, actually did not have faulty valve guides and did not need replacement.

4) Wiggle Testing is "out" at GM. In early March, GM released to its dealers an update to ESI mandating a new procedure for measuring stem-to-guide clearance for warranty purposes in all high-performance engines. It requires a hole gauge to measure guides and a micrometer to measure valve stems or a valve guide bore gauge, such as a Sunnun P310, and must be done with the heads removed and disassembled.

5) The demise of Wiggle Testing as a way to determine if guides are worn was a result of the LS7 Engineering Team's review of the LS7 article series, three CMM inspections of the heads removed from my engine in July of 2014 along with the Team's need for more accurate information from the field about warranty replacements of LS7 heads. Additionally, the LS7 Team's review of selected content on the CF, on another web site which also has a C6 Z06 forum and on additional web sites besides those two, may have influenced the decision.

5) According to Jordan Lee, the "machining error" stated here on the CF by Chevrolet Customer Service in October of 2012, was a failure of the supplier to properly deploy statistical process controls and, as a result, the diameters of valve guides in some, but not all, heads made during that period were machined too large.

6) The "suspect period" for this machining error, previously stated here on the CF and on other web sites by Chevrolet Customer Service to be 2008 to Feb 2011, is not correct. According to Chris Cogan, and confirmed by Jordan Lee, the suspect period was July, 2008 to March, 2009.

7) Only LS7 heads are manufactured by Linamar. LS9 cylinder heads were never manufactured by Linamar. LS9 heads were made in GM's engine plant in Silao, Mexico. I am partially responsible for that long-standing piece of misinformation. I apologize for any confusion it has caused.

8) The LS7 is currently manufactured at the Performance Build Center in Bowling Green and will remain so until the 5th Gen Camaro Z28 goes out of production.

I may post additional information concerning my 24 March visit to GM Powertrain as conditions warrant.

Thanks to the LS7 Engineering Team along with Tom Read, GMPT Director of Communications, for the time and resources they devoted to my visit with them in Michigan last week. I'd also like to thank the LS7 Team for their willingness to show me all the information they had available at the time of the meeting and their willingness to consider sharing additional information going forward. Finally, I appreciate the LS7 Team's interest in working with me to get as much information on LS7 valve guides as possible into the public domain.

thanks Hib - good info, as always. Is there a marking on the car to show when your build date occured?

What YEAR, or years. Have a pop corn, witch is; take me to the movies an sell me a story. Dont want to get into it but, here we go, pay out 76 an change, an with an 07 Z06, GM; when an how many miles with that warranty you offered to basic owners, like me, dont want to get upset with the bull ****.
THE BULL **** I HAD TO GO WITH MY 2004 Z06, HOLY CRAP. THATS WHAT I WILL CALL IT. BUY BACK AN THEN SELL IT OFF LIKE A TOY IN A. ANT FARM. 3 YEARS LATER, HAD TO DO,:cheers: 1800 LAW FIRM, AN THEN THEY.

Hib, some people may feel like they are having the wool pulled over their eyes but I think you have provided great feedback. I wonder how many heads were replaced or had non needed work done to them because of inaccurate wiggle tests that were never verified by a proper inspection using a guide bore gauge and micrometer? I suspect the number is quite high.

Another thing I picked up from the shop that measured the guides in my heads finding two intakes slightly outside the service tolerances. The owner said he had seen much worse on other engines that had run fine for many miles that way and he would feel comfortable just reassembling the heads and putting them back on the car, especially if it was a street only car or one that wouldn't see much track time.

We may have a simple case of public overreaction to a potential solution to the problem of dropped valve heads in some engines, especially ones that have seen extensive track time. The shop owner has emphasized to me weakening of valve springs over time could be the major culprit behind those failures just like they have been on other engines over history.

Bill

Personally, I think GM's decision to abandon wiggle testing is based SOLEY on minimizing financial losses with very little to do with accuracy. I will continue to do the wiggle test on my engine with 100% confidence in trusting the results.

The only way to tell if GM is lying is if their lips are moving!

Thanks for sharing your information. My engine was modified by the original owner, and after reading all the issues I had my heads done just for the sake it was not an oem piece. Upon disassembly, nothing was found to be out of spec., just my wallet. 2009 Z06 built in 11/08 :crazy:

My car is within the "window" period, but was out of warranty based soley upon age. No wiggle test done.......precise measurements off the car showed out of spec guides. My question is, was there any discussion about compensating those who have fixed the admitted problem once the warranty period is over?

My question then, would be why not recall those cars produced during the 2008-2009 period and fix them under warranty. And why not publish that information so that all the other owners would know. I maintained all along that a company like GM could identify the cars affected, if u are a manufacturing plant today you have that traceability.

Excellent info Hib.

I wonder though, as Bill indicates, and because "wiggle testing" has been promoted so strongly in here, just how long it will take for the point to be gotten across that it is, I believe you described it as; "at best inaccurate and in many cases unreliable".

Unfortunately, people are still going to spend money having it done and believing the results and hanging their hats on those results.

However your information may go a bit further in deterring DIYers, at least initially, before it has the effect of slowing those owners ready to open their wallets and eagerly looking for a place to "have the wiggle test done".

Your question above in bold is a good one, and the rest of your comments are interesting as well.

The potential use of the "wiggle test" as a revenue generator and tool to upsell a customer into cylinder head work, either deliberately, or as a result of error and/or inaccuracy is a consideration that I look at when I read some of these threads.

For those who are leaning toward believing that GM is deciding to completely nix the wiggle test as of late and only to limit financial losses, or because they don't truly believe that the test is a poor way to obtain a consistently useful interpretation of existing guide wear, well one might consider that Katech does not, and from all that I can find in here, seems to never have offered the "wiggle test" to evaluate guide wear, and that they apparently do not offer the "wiggle tests" as a service.

So it's not just GM who apparently sees the limited usefulness and potential pitfalls with this "test" as a consistently reliable means of determining valve guide wear, or even a method that should be part of their recommended or routine shop operating procedure in determining guide wear.

To say nothing as to if it "the wiggle test" is even a reliable predictor of outcomes to begin with, since that key point is yet to be determined in evaluating it's usefulness.

I hope GM plans on reimbursing those that spent money out of pocket for fixing the problem. My engine was a 12/08 build and could easily see the movement on a few valves with the spring still on.

That issue was not discussed in the meeting I had at GM Powertrain.

It would have been impossible such a discussion because no one in the meeting had anything to do with customer care, warranty administration or GM Legal. The only GM personnel present were engineers, Inspection Dept. employees and one guy who works with service information.

Thanks for the information. I look forward to reading your revised articles.

That depends on how quickly people accept that using a hole gauge and a mic or a valve guide bore gauge (i.e.: Sunnen P310) are much better ways.

Watching one of my heads get measured with a CMM and seeing the CMM data, there's no question that Wiggle Testing is at best inaccurate and in many cases unreliable if the point of the test is to decide on a head repair/replacement.

At this point, my belief is that would be unwise

One reason I made the OP was my hope that other DIYs won't make the same mistake I made, i.e.: putting too much faith in Wiggle Testing

Bam!
You get the Sunday morning Beacon of Reality Award "'06 Quicksilver Z06".

I suspect that, either unintentionally, out of ignorance, or intentionally, some independent service shops, including some who sponsor this web site, will continue to Wiggle Test.

:iagree: Thanks Hib! :thumbs:

Thank you for sharing this information. It is becoming encouraging again this issue/topic may be resolved once and for all.

Possibly your reference to future articles may include the findings of the LS7 measurements, but is there any preliminary feedback relative to the valve seat and/or rocker arm pedestal?

Thanks

There's two kinds of "wiggle" tests. There's the one where you are collecting numbers for the bean counters and there's the other where you just lost a tool between the valve stem and guide. The second of which doesn't require a degree in engineering to know you have a problem:rofl:

As far as the reported effected years go, I'd like to see a graph showing years on one side and the number of dropped valves on the other to see if it comes close to what GM said. There has been a number of dropped valves outside what they have said.

All that to inform the public that "wiggle testing" is not accurate?? Duh. Many of us (who actually do know how, and actually do use precision instruments) have been saying that ever since that GM procedure was introduced. The only "new" news here, is that GM is saying it isn't accurate.

The test however, is still a damn good, and damn simple/quick way to check and find out if you have excessive wear, and if you should yank the heads off or not. Accurate???? NO!!! But good enough to be leading indicator of imminent failure?? YES!!

Whether or not some vendors and shops are dishonest and will take advantage of people is a completely different topic. That's the end user/owner's accountability. The accountability to educate themselves.

Thanks for sharing this information Hib. :thumbs:

Hib,
I thought you validated your wiggle test using the test indicator method by having measurements done by your machinist on your removed heads.
Is the test indicator method inaccurate also?

"According to Chris Cogan, and confirmed by Jordan Lee, the suspect period was July, 2008 to March, 2009."



So according to these dates, the only Z owners that should be concerned are 2009's and maybe some early 2010's. That's going to surprise a lot of people. Especially the owners of other years that dropped a valve. Must be all the internet hysteria going around.