Hib Halverson

Please, DO NOT misquote me.

I have never stated that the set of replacement heads discussed in my articles and which had excessive valve seat runout were "2013 heads from GM".

It is true, the replacement heads were "...new, out of the box...", but they were very early heads which had been on she shelf at some GM Parts warehouse for a many years before they were shipped to my dealer.

I know that because the heads had the rear coolant holes threaded for the steam cross over which was once installed at the back of the engine. That cross over was eliminated early in LS7 production and after that, GM stopped threading those holes and plugged them.

And, while we are on the subject of my being misquoted...I never "bought" those heads. They were warranty replacements supplied by GM.

grcor

Hib, thanks for the information, but it still leaves me with a lot of questions.

1. “According to Chris Cogan, and confirmed by Jordan Lee, the suspect period was July, 2008 to March, 2009” for valve guides being machined incorrectly. Then why are so many valve guides over the service limit and dropped valves with heads built outside of this range? I hope your future posts will talk about other know issues like concentricity and quality problems with the exhausts valves that effect all LS7’s.

2. Everyone is using the service limit as the point at which the head should be rebuilt or replace. But it seems no one knows for sure at what measurement the valve guides have to be to cause a valve to break. It could be less than the service limit. With the quality control problems (variation of wall thickness and variation in weight) of the exhaust valves, is it even possible to give one number for all cases?

3. It’s not practical to pull the heads every 5 to 10 thousand miles and measure the valve guides.

4. What is an owner of a LS7 engine, whose warranty has expired, supposed to do? It is no fun driving the car when in the back of your mind you are wondering if you about to drop a valve.

reasonable suspicion

This is actually ridiculous. Divide and conquer they say.....

Pay no attention to the man behind the curtain, as he is not responsible, even for the admitted bad "window" area. LOL

pewter99

I was unaware of the warnings but if people want the info about their Corvette they need to take Action

Dirty Howie

Are they aware of the actual number of heads out of spec as confirmed by measuring the guide clearance by head shops? Are they disputing this data? If not why don't they see this as a prevelant condition?


DH

2k Cobra

I stand corrected. However they replaced "Bad" heads with "Bad" heads.

It was another member, Seb that bought a set of new set of "Bad" heads that were dated 2013.

Pretty weak coming from an automaker that the taxpayer bailed out..

ccryder

Careful with this info....
The little decal on the front of your engine will only tell you when your LS7 engine was built/assembled at the Wixom Performance Center... because that is when they apply the build sticker on your drivers side head.... what that won't tell you is the actiual manufacture date of your heads. And I have yet to see anybody who has deciphered the actual machining numbers that exist on our OEM heads....that translate to mfg dates.

However, as an example, if you have an engine with a build date of July 2008, it is very highly likely your heads where mfg in the previous 30-90 day date ranges....before they showed up at the Wixom plant for engine assembly. When I toured the Wixom performance center in early April of 2010, there were literally pallets of heads staged on the floor (LS7 & LS9) ready for engine builds.

So if the "head manufacture suspect dates" are July 08 to March 09....some very early built June 2008 (09 model year Z's) likely have heads that were mfg in May, April or even March...for early June engine and car build dates.....and placing those cars/engines out of the suspect head mfg date ranges.

If GM has "really dialed in" on the exact months of the suspect mfg dates of heads with the machining errors (as stated) they should be able to supply us with a fairly accurate range of VIN and/or engine build dates of the cars that very likely have these "suspect" heads on them.....any talk of that at the round table Hib??

Dan_the_C5_Man

Very disappointing to say the least - a meeting with folks that might actually have the ability to understand and address the issue, and the best they could come up with is to try and convince us (and themselves) that the problem really isn't one, based on measuring a head that was borderline (and just how many miles were on that particular head anyway? My guess is you could have received a clearly negative result if you'd only waited a few more thousand miles, which is ridiculous).

This just reinforces my position that we are on our own in this - keep your heads buried and drop a valve, or stay vigilant and address the problem before it becomes catastrophic.

rickyb

Hib, Thanks so much for taking this so seriously and taking time to investigate this issue, for we do not have the time to do so. We appreciate your efforts most sincerely!

RobsVette04

Is this English?

Michael_D

Don't bother with him. It's pointless and he's just up to his old tricks yet once again, trying to bait and pick a fight with me, but knowing he's on my ignore list, he is now using you to quote him.

The concept is soooooo....... simple, there's no need to argue about it, because most people with enough intellect to read, can figure it out for themselves. (most, but obviously not one)

Prove that significant guide wear will result in a failure, and that a wiggle test will indicate significant guide wear? Why on earth would that need to be "proved"? Do I need to "prove" that if you don't put gas in your gas tank, that you'll run out of gas?

Hib Halverson

That's the best question about my OP which I've read so far. My compliments to you for carefully reading the Wiggle Test article.

My investigation of the "test indicator" method was driven by my frustration with the inaccuracy of Wiggle Testing with a dial indicator and did not occur until a number of months after my heads were replaced under warranty, so....No. I did not validate the indicator method with bore gauge guide measurements Mark DeGroff Cylinder Head Service took on my "removed heads".

After the warranty work on my car was completed, I did attempt to validate the test indicator method of checking stem-to-guide clearance by measuring the #6 intake valve's guide clearance in my replacement heads after they'd been put on the car. First, I Wiggle Tested that valve according to the procedure posted by American Heritage, then I checked it with dial indicator procedure used in my Wiggle Test article. Finally, I checked it with the "test indicator method" (which by then, I had adopted as the best way). I compared that data to what DeGroff Cylinder Head Service had measured when they they assembled the replacement heads. In that instance, only the "test indicator method" repeatedly read the same as a Sunnen P-310 measurement taken at the center of that same valve guide during the assembly of the heads prior to their installation. The readings, from the two methods ("test indicator" and bore gauge) for stem-to-guide clearance of my #6 intake were .0025-in.

Some rules have exceptions and I suppose the "test indicator method," as discussed in my article about measuring stem-to-guide clearance on another web site, might be the one exception to my statement in this thread's OP that Wiggle Testing is, "....in most cases, unreliable."

In most cases, advanced DIYs, professional service technicians and even the engineers who met with me at GM Powertrain last week understand "Wiggle Testing" as being done with a dial indicator which is forced by the LS7's head architecture to be set-up such that its direction of measurement is at a significant angle to movement of the valve being wiggled. Also, few Wiggle Testers mount the indicator on a vertical post screwed directly into the head. Most use a flexible arm indicator base clamped by a "vise grip" to a bolt screwed into the head or to the head structure itself or they use a magnetic base attached to a flat plate bolted or clamped to the head. The bottom line, here, is that Wiggle Testing like that is, in most cases, unreliable because of the significant errors which can occur because of indicator pintle angle to vector of the movement being measured, indicator base or flexible arm movement, inaccurate measurement of distance between the indicator pintle contact point on the valve, failure to move the valve just off the seat before wiggling it and applying excessive force to the valve during wiggling such that the stem bends slightly.

I believe when GM Powertrain considered all that, in order to more accurately diagnose engines with worn valve guides for warranty purposes in the field, it decided to change the required method for measuring stem-to-guide clearance from the Wiggle Test, which has been a part of GM service data for a long time, to a "bore gauge test". How long have GM techs been "wiggling"? I went back to the beginning of the Gen 3 era, 1997. What did I find for measuring guide clearance? The Wiggle Test. I went back another ten years to 1987. Back then, they were wiggling, too. I went back another five years to the 1982 FSM and, in its instructions on how to measure stem-to-guide clearance, I found the Wiggle Test, complete with an illustration showing a dial indicator set up much like what was in GM ESI up until just a few weeks ago. Back beyond '82, I do not have FSMs for each year. The next Service Manual I have is 1971 and it shows the Wiggle Test. The oldest FSM I have on file is from 1963 and it advocates using a small expanding hole gauge and a micrometer to measure the guide diameter and a mic to measure the valve stem which, back then, was the best method of measuring stem-to-guide clearance the metrology of that period could provide. With the Gen 1 Small-Block V8s (1955 to 1991) and the Mark IV-VI, Big-Block V8s (1965-2000), Wiggle Testing was more practical because the head architecture allowed one to set up a dial indicator 90° to the valve stem and measure right at the top of the guide, which you cannot do with LS7 heads, but,...I digress.

if you're measuring stem-to-guide clearance, with the engine in the car, and you are using a test indicator mounted as instructed in my article, it's likely the data you get will be fairly accurate. How accurate? Well, as I said above, I validated it with bore gauging the same valve, but that's only one measurement. Anyone attempting to "scientifically" assess the accuracy of that method will validate it by measuring more than one valve, so my "argument" might be a bit weak and...is moot at this point, if we are talking about using the "test indicator" method as a way to justify a warranty claim for worn guides, because GM will not longer accept anything other than using a bore gauge.

Now...if the need for stem-to-guide clearance testing is driven by either: 1) an out-of-warranty engine showing symptoms of guide wear (excessive valve noise, etc) or 2) an out-of-warranty engine which has no symptoms of guide wear but who's owner wants clearances checked because he/she is concerned about the wear issue, and it's not practical or affordable to remove the heads; then, the only way I would consider to measure the clearance would be the "test indicator" method. I would not do a "traditional" Wiggle Test using a dial indicator because it can be so inaccurate.

Hib Halverson

The head which was run on the CMM at GM Powertrain had been in service for 16,334 miles.

AZDANZ06

GM is trying to cover their A$$ at this point getting rid of the wiggle test

Hib Halverson

Oh wow, there's another great question. My future posts here on the CF will, of course, be brief. They will likely cover concentricity but will not cover "quality problems" with exhaust valves.

I will not speculate on when valves may fail.

I agree...wholeheartedly!

If the engine is out of warranty and the owner wants to know stem-to-guide clearances, I recommend the "test indicator" method of measuring those clearances which is detailed in the article I posted on another web site.

Bill Dearborn

I would like to comment on your very good questions since I am going through this right now.

My engine builder pulled the heads on my 2011 GM replacement engine a couple of weeks ago. A couple of Intake guides were .0002 out of the service spec. He said he didn't believe there were going to any problems buttoning everything back up.

Like you say GM recommends replacing the heads if guides are found outside the service spec but my engine builder says he has seen much worse without an engine failure. The GM spec is one of those indicators that if you are repairing an engine and find a guide outside that spec you do something about it. It doesn't represent impending doom.

It isn't practical to check the guides every 10 to 15K miles even with the wiggle test since it can cost almost as much as pulling the heads to do it properly across all 16 valves. I am going with Ti/Mo intake and exhaust valves and bronze guides in my heads due to the way I use the car and my builder says the most important thing to do is to keep tabs on the valve springs and make sure they are maintaining proper spring pressure. He recommends checking them at least once per year because of the way I use the car. On a street only car he wouldn't recommend that.

How many street driven cars with stock engines have dropped a valve? Very few if any (this is hard to pin down). How many street driven cars that have an aftermarket cam installed have dropped a valve? From what has been posted on the forum there are some but I think this follows the line my builder has been telling me about valve spring life becoming an issue depending on the valve train selected and the spring pressures required.

How many cars that have been regularly tracked have dropped valves. From my personal knowledge I know of 9 including mine. There have been many more reported on the forum. Some of them may not have happened at the track but on a city street while driving slow but the common thread has been heavy track usage with the engines being run at high rpms for long periods of time, with lots of downshifting (which my engine builder says puts more stress on the engine even when done with out mechanically over revving the engine).

If you are just using the car on the street and it doesn't have a history of track usage and is completely stock I doubt you have a lot to be concerned about. Will a totally stock street driven engine drop a valve? Yes. But, that also happens to a certain percentage of plain jane grocery getters that are driven to and from work every day.

Bill

vray

Thanks for the info Hib. Luckily my LS7 build date was 11 Dec 2007, so I have absolutely nothing to worry about.

MUKAK

i still dont understand why the LS7s tend to drop valves where other LS series motors dont.. my C5 LS1 had 150k miles with lots of track abuse, never dropped a valve

so after all these years no1 knows ( including GM ) why LS7 drops valves?

grcor

This is the best description of the problem. http://www.corvetteactioncenter.com/...-engine18.html

Javvy

First point Bill, mine, 2007, 16,000 miles, never tracked, never abused, grenaded the
engine at 60mph changing into 4th gear !!!!!!! Spun across a roundabout.....missed everything!

Second point, I believe I have a hell of a lot to be concerned about.
The replacement engine and ancilliaries are from 2010.