[ANSWERED] C6 Z06 Question for Tadge Juechter
02-18-2015, 04:35 PM
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[ANSWERED] C6 Z06 Question for Tadge Juechter
Original question is here.
AZDANZ06 asked:
I am writing to you on behalf of all C6 Z06 Owners here at the Corvette Forum. There has been way too many C6 Z06 owners that have suffered LS7 engine failures due to dropped valves. GM claims that there was a manufacturing problem that was subsequently corrected, yet engines and off the shelf replacement cylinder heads produced after that date are also failing at an alarming rate. Loyal owners of even extremely low mileage vehicles are continuing to measure valve-to-guide clearances far beyond service limits and have had their heads reworked at a significant cost. This is evidenced by a cross section of Corvette Forum Members who have had their valve-to-guide clearances measured, 88% of the 208 member cars checked have had out of spec valve guides on C6 Z06's built from 2006 through 2013. With the apparent widespread incidence of excessive valve guide wear among LS7's, does GM know anything regarding the root cause of the issue and/or potential mitigation actions in order for LS7 owners to regain confidence in the platform and to retain loyal GM Customers?
I am writing to you on behalf of all C6 Z06 Owners here at the Corvette Forum. There has been way too many C6 Z06 owners that have suffered LS7 engine failures due to dropped valves. GM claims that there was a manufacturing problem that was subsequently corrected, yet engines and off the shelf replacement cylinder heads produced after that date are also failing at an alarming rate. Loyal owners of even extremely low mileage vehicles are continuing to measure valve-to-guide clearances far beyond service limits and have had their heads reworked at a significant cost. This is evidenced by a cross section of Corvette Forum Members who have had their valve-to-guide clearances measured, 88% of the 208 member cars checked have had out of spec valve guides on C6 Z06's built from 2006 through 2013. With the apparent widespread incidence of excessive valve guide wear among LS7's, does GM know anything regarding the root cause of the issue and/or potential mitigation actions in order for LS7 owners to regain confidence in the platform and to retain loyal GM Customers?
Tadge answered:
First of all, let me explain why it is taking longer to answer this question than the usual week. It is my intention to use this part of the forum to get the best, most accurate information to the Corvette community I can. Some questions, like this one, require a number of internal experts be consulted for a complete answer and so it takes longer for everyone to weigh in.
I purchased a 2006 Z06 myself. It was my pride and joy. I sold it a couple years ago in anticipation of buying a C7. I sold it to Damian Zink, who works in Bowling Green and is continuing to use it on road and track. I’m very happy it is still in the Corvette team family. I tell you this to counter a prevailing assumption on the forum and elsewhere that we on the Corvette team only care about selling new cars. Nothing could be farther from the truth. Many of us are customers ourselves, our friends and families own a lot of cars from many generations and we have long term relationships with many of our customers. The long term ownership experience is very important to us – even well beyond the warranty period.
Engine reliability is a huge focus for us and we have been monitoring the LS7 since it was introduced. We will continue to do so for the foreseeable future. I can promise any learning we have will be incorporated into our future designs and we will make every attempt to treat customers fairly.
The description of the LS7 experience below is being provided by my counterpart on the engine side, Jordan Lee, the Small block Chief Engineer:
The LS7 engine is a high performance engine, our highest output naturally aspirated engine in production today. It achieves its power output by incorporating very large titanium intake valves and a very aggressive camshaft profile. As a result, the LS7 does exhibit more valve train noise than our other Small Block variants. The large valves and the rapid open and closing events of the valves will result in valve train tick. All LS7 engines exhibit this valve train noise. The cylinder head is also quite unique compared to our other Small Block variants. The head is CNC machined, including the ports, by one of our reputable suppliers. They fully machine the cylinder head, including the valve guide ID, then they assemble the head with valves and springs and deliver the fully assembled cylinder head to our engine assembly plant.
Like all manufacturers, we have specifications and tolerances for all critical dimensions including the valve guide ID. Unfortunately for a 9 month period of time, from July 2008 to March 2009 we have evidence that some cylinder heads (a small percentage of the total population) were delivered to our assembly plant with valve guide ID’s that were out of specification and were over-sized. This resulted in more valve train noise than is normal. Once the “out of specification” condition of the valve guide ID was identified, we worked with our dealerships to repair customer cars when we identified engines that had out of specification cylinder heads. For the 2009 MY we replaced a total of 65 cylinder heads (Z06 production was 1654 cars and most heads were replaced in pairs so roughly 33 engines). Due to this valve guide ID issue, our cylinder head supplier implemented more rigorous inspections and quality check procedures to ensure they made and shipped only cylinder heads that are within specification. After the time period in question the number of customer complaints dropped significantly.
One issue we struggled with was defining an inspection procedure that the dealership can perform to determine if the guides are out of spec. The only accurate method to measure valve guide ID is to remove the head from the engine, remove the valves, and use a dial-bore gauge or CMM (Coordinate Measuring Machine) to accurately measure the ID. This method requires a lot of disassembly of the engine and many customers don’t want the heads removed for inspection. As a result, we developed another technique fondly known as the “wiggle method” where the valve spring is removed and the valve is wiggled in the guide, and the distance is measured with a dial indicator and then using trigonometry the clearance is calculated. Unfortunately this method is not very accurate and has a tendency to indicate a larger guide internal diameter than it actually is. We know this for a fact because we tested the method by using the wiggle method on a few cylinder heads and then disassembled the heads and measured them on a CMM (Coordinate Measuring Machine) for an accurate measurement and then compared the results between the two techniques. We’re currently investigating other techniques to get a better measurement without disassembling the cylinder heads and will instruct our dealerships accordingly if we are able to develop one. To date we have not been successful in developing an accurate non-intrusive technique. Since there is significant error in the wiggle method we are contemplating whether we should continue with this method.
Regarding valve guide material, the LS7 uses a premium guide material, Federal Mogul PMF10 which is oil impregnated and has a high moly content. We look at our warranty claim data almost daily looking for trends and problems and do act as quickly as possible to make sure our customers are taken care of and we fix any known problems ASAP. Based on the data we’ve amassed to date, it still appears that our suspect period is July 2008 to March 2009. Worth noting is that most of the heads made in this time frame are indeed within specification. We stand behind our products and our customers, and will repair under warranty any cylinder heads whose guides are indeed out of specification within the Powertrain warranty period.
First of all, let me explain why it is taking longer to answer this question than the usual week. It is my intention to use this part of the forum to get the best, most accurate information to the Corvette community I can. Some questions, like this one, require a number of internal experts be consulted for a complete answer and so it takes longer for everyone to weigh in.
I purchased a 2006 Z06 myself. It was my pride and joy. I sold it a couple years ago in anticipation of buying a C7. I sold it to Damian Zink, who works in Bowling Green and is continuing to use it on road and track. I’m very happy it is still in the Corvette team family. I tell you this to counter a prevailing assumption on the forum and elsewhere that we on the Corvette team only care about selling new cars. Nothing could be farther from the truth. Many of us are customers ourselves, our friends and families own a lot of cars from many generations and we have long term relationships with many of our customers. The long term ownership experience is very important to us – even well beyond the warranty period.
Engine reliability is a huge focus for us and we have been monitoring the LS7 since it was introduced. We will continue to do so for the foreseeable future. I can promise any learning we have will be incorporated into our future designs and we will make every attempt to treat customers fairly.
The description of the LS7 experience below is being provided by my counterpart on the engine side, Jordan Lee, the Small block Chief Engineer:
The LS7 engine is a high performance engine, our highest output naturally aspirated engine in production today. It achieves its power output by incorporating very large titanium intake valves and a very aggressive camshaft profile. As a result, the LS7 does exhibit more valve train noise than our other Small Block variants. The large valves and the rapid open and closing events of the valves will result in valve train tick. All LS7 engines exhibit this valve train noise. The cylinder head is also quite unique compared to our other Small Block variants. The head is CNC machined, including the ports, by one of our reputable suppliers. They fully machine the cylinder head, including the valve guide ID, then they assemble the head with valves and springs and deliver the fully assembled cylinder head to our engine assembly plant.
Like all manufacturers, we have specifications and tolerances for all critical dimensions including the valve guide ID. Unfortunately for a 9 month period of time, from July 2008 to March 2009 we have evidence that some cylinder heads (a small percentage of the total population) were delivered to our assembly plant with valve guide ID’s that were out of specification and were over-sized. This resulted in more valve train noise than is normal. Once the “out of specification” condition of the valve guide ID was identified, we worked with our dealerships to repair customer cars when we identified engines that had out of specification cylinder heads. For the 2009 MY we replaced a total of 65 cylinder heads (Z06 production was 1654 cars and most heads were replaced in pairs so roughly 33 engines). Due to this valve guide ID issue, our cylinder head supplier implemented more rigorous inspections and quality check procedures to ensure they made and shipped only cylinder heads that are within specification. After the time period in question the number of customer complaints dropped significantly.
One issue we struggled with was defining an inspection procedure that the dealership can perform to determine if the guides are out of spec. The only accurate method to measure valve guide ID is to remove the head from the engine, remove the valves, and use a dial-bore gauge or CMM (Coordinate Measuring Machine) to accurately measure the ID. This method requires a lot of disassembly of the engine and many customers don’t want the heads removed for inspection. As a result, we developed another technique fondly known as the “wiggle method” where the valve spring is removed and the valve is wiggled in the guide, and the distance is measured with a dial indicator and then using trigonometry the clearance is calculated. Unfortunately this method is not very accurate and has a tendency to indicate a larger guide internal diameter than it actually is. We know this for a fact because we tested the method by using the wiggle method on a few cylinder heads and then disassembled the heads and measured them on a CMM (Coordinate Measuring Machine) for an accurate measurement and then compared the results between the two techniques. We’re currently investigating other techniques to get a better measurement without disassembling the cylinder heads and will instruct our dealerships accordingly if we are able to develop one. To date we have not been successful in developing an accurate non-intrusive technique. Since there is significant error in the wiggle method we are contemplating whether we should continue with this method.
Regarding valve guide material, the LS7 uses a premium guide material, Federal Mogul PMF10 which is oil impregnated and has a high moly content. We look at our warranty claim data almost daily looking for trends and problems and do act as quickly as possible to make sure our customers are taken care of and we fix any known problems ASAP. Based on the data we’ve amassed to date, it still appears that our suspect period is July 2008 to March 2009. Worth noting is that most of the heads made in this time frame are indeed within specification. We stand behind our products and our customers, and will repair under warranty any cylinder heads whose guides are indeed out of specification within the Powertrain warranty period.
02-18-2015, 04:40 PM
#2
Team Owner
cliffs: in warranty OK....out of warranty on your own
and this statement is in conflict with previous statement about heads being fixed after 2011
also of note doesn't address the recently purchased heads that were out of spec...
and this statement is in conflict with previous statement about heads being fixed after 2011
also of note doesn't address the recently purchased heads that were out of spec...
Last edited by pewter99; 02-18-2015 at 04:46 PM.
02-18-2015, 04:56 PM
#6
Le Mans Master
According to his note the suspect engines were made July 2008 thru March 2009 so that seems to indicate that model year 2009 has the problem. Apparently all the other years do not have a problem and he provided no data for the other years. I don't think many will be surprised by the lack of any useful information that can help the owners. As pewter99 says if you are in warranty don't worry if out of warranty its your money. Thanks GM. 
Last edited by b4i4getit; 02-18-2015 at 05:00 PM.
02-18-2015, 05:16 PM
#7
Melting Slicks
Absolutely nothing there that is worthwhile or meaningful.
It also doesn't address the hundreds of heads that have been removed and measured by tests other than the wiggle method, and found well out of spec.
It also doesn't address the hundreds of heads that have been removed and measured by tests other than the wiggle method, and found well out of spec.
Last edited by atljar; 02-18-2015 at 05:22 PM.
02-18-2015, 06:02 PM
#11
Racer
"Unfortunately for a 9 month period of time, from July 2008 to March 2009 we have evidence that some cylinder heads (a small percentage of the total population) were delivered to our assembly plant with valve guide ID’s that were out of specification and were over-sized. This resulted in more valve train noise than is normal. Once the “out of specification” condition of the valve guide ID was identified, we worked with our dealerships to repair customer cars when we identified engines that had out of specification cylinder heads."
--Wonder what that "evidence" was - gives me the feeling they really don't know for sure how large the impact is.
--If there was strong evidence of a real problem and really worked with their delearships, then I would think that all LS7's made in that time frame would have been brought in and inspected, no? I imagine they would have a way to determine which motors went into which cars, so they could identify and contact each and every owner to verify with. From what I understand, only when customers called in with broken cars did they do anything about it - luckily without any injuries.
--Wonder what that "evidence" was - gives me the feeling they really don't know for sure how large the impact is.
--If there was strong evidence of a real problem and really worked with their delearships, then I would think that all LS7's made in that time frame would have been brought in and inspected, no? I imagine they would have a way to determine which motors went into which cars, so they could identify and contact each and every owner to verify with. From what I understand, only when customers called in with broken cars did they do anything about it - luckily without any injuries.
02-18-2015, 06:18 PM
#13
Team Owner
So after reading this I would be concerned that GM will stop doing the Wiggle test as a means to replace the heads. And instead require that the customer pays for complete head removal to confirm guides are out of spec. That would be a huge increased burdon on the customer.
Since they have actually compared the Wiggle test to actual measurements it seems that they should at least be able to come up with a conversion factor threshold. That should enable them to continue the simple Wiggle test to determine when heads need to be replaced.
Have we had any Wiggle tests that were bad and later found the guides to actually be in spec when measured with heads off
DH
Since they have actually compared the Wiggle test to actual measurements it seems that they should at least be able to come up with a conversion factor threshold. That should enable them to continue the simple Wiggle test to determine when heads need to be replaced.
Have we had any Wiggle tests that were bad and later found the guides to actually be in spec when measured with heads off
DH
02-18-2015, 06:48 PM
#14
Melting Slicks
Member Since: Jan 2013
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My z was built within the time frame mentioned in the reply. The guides were bad when measured off the car. However even though it had only 7800 miles on it, the warranty has lapsed from age. So even though they admit the problem, sorry you are on your own.
I believe we should seek legal advice as others have mentioned. Sad really. But as expected.
I know this will be my last new gm product.
I believe we should seek legal advice as others have mentioned. Sad really. But as expected.
I know this will be my last new gm product.
02-18-2015, 06:54 PM
#15
Melting Slicks
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"Unfortunately for a 9 month period of time, from July 2008 to March 2009 we have evidence that some cylinder heads (a small percentage of the total population) were delivered to our assembly plant with valve guide ID’s that were out of specification and were over-sized. This resulted in more valve train noise than is normal. Once the “out of specification” condition of the valve guide ID was identified, we worked with our dealerships to repair customer cars when we identified engines that had out of specification cylinder heads."
--Wonder what that "evidence" was - gives me the feeling they really don't know for sure how large the impact is.
--If there was strong evidence of a real problem and really worked with their delearships, then I would think that all LS7's made in that time frame would have been brought in and inspected, no? I imagine they would have a way to determine which motors went into which cars, so they could identify and contact each and every owner to verify with. From what I understand, only when customers called in with broken cars did they do anything about it - luckily without any injuries.
--Wonder what that "evidence" was - gives me the feeling they really don't know for sure how large the impact is.
--If there was strong evidence of a real problem and really worked with their delearships, then I would think that all LS7's made in that time frame would have been brought in and inspected, no? I imagine they would have a way to determine which motors went into which cars, so they could identify and contact each and every owner to verify with. From what I understand, only when customers called in with broken cars did they do anything about it - luckily without any injuries.
02-18-2015, 07:44 PM
#18
Team Owner
My 2008 was out of warranty because of years, not the 27,000 miles I have on it. Anyone know the Law Firm that handled the Porsche case? I will spearhead getting something going.
It would be easier at this point for GM to offer to reimburse those of us who have a receipt for getting our heads reworked and to take care of all Z06 Owners who need them done.
It would be easier at this point for GM to offer to reimburse those of us who have a receipt for getting our heads reworked and to take care of all Z06 Owners who need them done.
You might want to point out to them that many if not all the failed motors (not included on your list) were likely do to the same issue.
DH
02-18-2015, 07:47 PM
#19
Thanks azdan, all we need to do is get the ball rolling. They clearly don't care and/or think it'll be cheaper to just have a class action lawsuit against them.
The only thing the can gain by recalling or reimbursing the people who have paid is to save their reputation. It would be a good move considering what just happened with the ignition switches but it doesn't seem like they're wise enough.
The only thing the can gain by recalling or reimbursing the people who have paid is to save their reputation. It would be a good move considering what just happened with the ignition switches but it doesn't seem like they're wise enough.
