Wiggle Testing: How to Perform On-Engine Test for C6 Corvette LS7 Valve Stem-Guide Clearance

[Rob]

Wiggle Testing: How to Perform On-Engine Test for C6 Corvette LS7 Valve Stem-Guide Clearance:

Corvette Action Center | Tech Center | Research Center | 2005 - 2013 Corvette Center | Wiggle Testing - How to Perform the On-Engine Test for LS7 Valve Stem to Guide Clearance - Page 1 of 4

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[LLC5]

I doubt if GM is going to do any warranty work with a DIY test from an independent shop or an owner, I am sure that it would need to be verified by a certified GM tech along with a tech line or DSM ok to do the work.

Wonder what flat rate time is for that procedure, or if there is one? To do it correctly is very time consuming, to do it with out bending a valve even more so.....

 

[kpic]

Hib,
Kudos for the excellent write up.

I doubt if GM is going to do any warranty work with a DIY test from an independent shop or an owner, I am sure that it would need to be verified by a certified GM tech along with a tech line or DSM ok to do the work.

Wonder what flat rate time is for that procedure, or if there is one? To do it correctly is very time consuming, to do it with out bending a valve even more so.....

Oh, I am sure they have one and just as sure one can rebuild a head for less.

They would use a valve guide bore gage which requires the head to be off and the valves out. A .001' to 1.000" is more for measuring lift or shimming valve springs to set coil spacing at lift. A valve guide bore gage reads increments of .0001".

 

[LLC5]

I forgot to mention about the great write up and excellent information in my last post, very well done for sure Hib.

I was thinking the same thing as kpic, by the time you pay someone to do the test properly (and hopefully NOT bend any valves, which is way too easy to do) you could have just invested in the repair. Under warranty though would obviously be a different story, first the test procedure would have to start out as customer pay for the diagnosis at a GM certified dealer, and then hopefully the tech would reach the same test numbers that you previously paid someone (or performed yourself) else to do.

Either way, excellent article.

 

[kpic]

My wants and inability to pay for what I wanted was how I learned to turn a wrench.

 

[7thz16]

Wiggle Testing: How to Perform On-Engine Test for C6 Corvette LS7 Valve Stem-Guide Clearance:

Corvette Action Center | Tech Center | Research Center | 2005 - 2013 Corvette Center | Wiggle Testing - How to Perform the On-Engine Test for LS7 Valve Stem to Guide Clearance - Page 1 of 4

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"We recommend wiggle testing any LS-7 which has more than 10,000 miles on it". How was this conclusion arrrived at? Is there data to support the need for this test at 10,000 miles on all LS-7's? If yes, can we ask you to share that information? THANKS!

Merry Christmas!

 

[rkoblin]

Wiggle Test

As a person who has limited mechanical skill. What symptoms would I be looking for
to have to take my car back to the dealer. My 2015 has 1200 miles and is running
flawlessly.
Thanks
Rich
Aiken SC

 

[Hib Halverson]

I doubt if GM is going to do any warranty work with a DIY test from an independent shop or an owner, I am sure that it would need to be verified by a certified GM tech along with a tech line or DSM ok to do the work.

Wonder what flat rate time is for that procedure, or if there is one? To do it correctly is very time consuming, to do it with out bending a valve even more so.....

The impetus for writing that article was to "answer" some of the incorrect descriptions of the stem-to-guide test procedure posted in various places around the web. One example of a wiggle test DIY thread that, if followed, results in incorrect measurement is on the Corvette Forum at LS7 Wiggle Test DIY

The article's main intent was to explain how to do the procedure correctly with the heads on the vehicle. The target audience was DIYs and independent service vendors who are working on an out-of-warranty engine or DIYs who want to prove to GM that their engine has a guide wear problem after a warranty claim is denied with the explanation that the engine is not: making noise, using oil and or turning on its MIL.

I don't know what the flat rate is, but it may be based on removing the heads from the engine which is the method GM implies in factory service data. If it is based on that, then it's actually going to be pretty high. In spite of the "heads-on" method I discuss in the story being difficult and time-consuming, it's still going to take less time than getting the heads off to measure stem-to-guide clearance. Also, if the point of the test is only to gain evidence to support a warranty claim, you only need to go far enough to find one or two bad guides and you're done. If there's one bad guide or 16 of them, GM is going to replace the heads.

 

[Hib Halverson]

"We recommend wiggle testing any LS-7 which has more than 10,000 miles on it". How was this conclusion arrrived at? Is there data to support the need for this test at 10,000 miles on all LS-7's? If yes, can we ask you to share that information? THANKS!

In the case of most engines which have the problem, by 10,000 miles you should be able to demonstrate it with measurements. Obviously, some engines have developed bad guides with much less miles on them and some with much more.

It depends on the rate of guide wear and many things can affect that but the main one is non-concentricity. If the level of non-concentricity is .001 then the guides are going to wear at a rate not much more rapidly than stock. If the level of non-concentricity is .007 then the guides are going to wear really fast.

Merry Christmas!

Big ole dittos!

 

[Hib Halverson]

As a person who has limited mechanical skill. What symptoms would I be looking for
to have to take my car back to the dealer. My 2015 has 1200 miles and is running
flawlessly.
Thanks
Rich
Aiken SC

Your engine does not have the problem.

The valve guide wear issue affects the LS7 engine in 2006-2013 Z06es. It does not affect the LT1 or LT4 in 2015s.

 

[kpic]

rkoblin
As yours is a 2015, you should not be affected.

Hello all,
LS7 Valve guide issue summary:
• Affects a small, number of '08, 09 ’10 and ’11 Z06’s
• GM discovered the condition through our cylinder head warranty data involving a very small percentage of our vehicles.
• Through inspection of returned heads, it was determined that a machining error in the valve guide had occurred at our head supplier.
• The quality issue has been contained as of Feb 2011 with 100% inspection of all heads.
• The most common customer complaint has been excessive valve train noise.
However if the condition is not addressed, it could result in engine failure. To date, where this condition has been observed, it has occurred early in the vehicle life.
What customers need to know: They should drive and enjoy their vehicles without fear. If their car demonstrates this condition, they are likely to hear unusual valvetrain noise first....
Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades - LS1TECH

The quote is from GM. The thread has some great pictures. However, after all the work of pulling the heads; I'd replace the guides, valves, and springs.

"it was determined that a machining error in the valve guide had occurred at our head supplier"

Doesn't make sense unless they meant when the guides are reamed?? That being said; industry has gone away from listing processes. Or if the drawing states ±0.007mm with a certain surface finish and the part meets the requirement; no one cares what process was used.

 

[rkoblin]

Wiggle Valves

Thanks for the answer. I feel better. No one want to have problems with their ride. Thanks again. Happy holiday

rich
Aiken SC

 

[7thz16]

"We recommend wiggle testing any LS-7 which has more than 10,000 miles on it". How was this conclusion arrrived at? Is there data to support the need for this test at 10,000 miles on all LS-7's? If yes, can we ask you to share that information? THANKS!

In the case of most engines which have the problem, by 10,000 miles you should be able to demonstrate it with measurements. Obviously, some engines have developed bad guides with much less miles on them and some with much more.

It depends on the rate of guide wear and many things can affect that but the main one is non-concentricity. If the level of non-concentricity is .001 then the guides are going to wear at a rate not much more rapidly than stock. If the level of non-concentricity is .007 then the guides are going to wear really fast.

Big ole dittos!

Thanks. So the 10K miles is not hard data but as GM states "where this condition has been observed, it has occurred early in the vehicle life". The type of miles (tracking vs. casual city / hwy) would likely impact that as well. As far as the "2006 to 2013 LS-7's", the post quoting GM appears to state that a limited number of '08, 09, ’10 and ’11's only may be affected.

 

[LLC5]

The impetus for writing that article was to "answer" some of the incorrect descriptions of the stem-to-guide test procedure posted in various places around the web. One example of a wiggle test DIY thread that, if followed, results in incorrect measurement is on the Corvette Forum at LS7 Wiggle Test DIY

The article's main intent was to explain how to do the procedure correctly with the heads on the vehicle. The target audience was DIYs and independent service vendors who are working on an out-of-warranty engine or DIYs who want to prove to GM that their engine has a guide wear problem after a warranty claim is denied with the explanation that the engine is not: making noise, using oil and or turning on its MIL.

I don't know what the flat rate is, but it may be based on removing the heads from the engine which is the method GM implies in factory service data. If it is based on that, then it's actually going to be pretty high. In spite of the "heads-on" method I discuss in the story being difficult and time-consuming, it's still going to take less time than getting the heads off to measure stem-to-guide clearance. Also, if the point of the test is only to gain evidence to support a warranty claim, you only need to go far enough to find one or two bad guides and you're done. If there's one bad guide or 16 of them, GM is going to replace the heads.

It is a very good article with excellent information.

Never thought about the "after a warranty claim is denied" aspect. This would be a good way to possibly get a claim started after a denial.

 

[73shark]

Anyone have a clue as to what the "machining error" was?

Great write-up!

 

[megavettes]

Wiggle Test

It is a very good article with excellent information.

Never thought about the "after a warranty claim is denied" aspect. This would be a good way to possibly get a claim started after a denial.

Great article Hib and thanks very much for writing it. I have an '08 Z06 with 16,000 miles on it and the valve train sounds as it did when new however, I'm almost afraid to drive it without doing a valve wiggle test. I checked with the owner of a Corvette repair shop in MD and he told me there is no doubt that all '06 through '11 LS7s will eventually have a problem whether you track the car or baby it. His recommendation is to just swap the heads with a new GM set, or well known after market supplier or, he can replace the valve guides in the existing heads, machine them to acceptable tolerances, and rebuild and reinstall the heads. The procedure runs $5K regardless of which route you take. All of the options are better than $10K for a new engine. Frankly, I am completely amazed that GM is aware of the problem and not stepping up to recall the cars. To have a situation that is there fault and in no way caused by or the result of abuse is despicable. I have lost all respect for the company.

 

[73shark]

Frankly, I am completely amazed that GM is aware of the problem and not stepping up to recall the cars. To have a situation that is there fault and in no way caused by or the result of abuse is despicable. I have lost all respect for the company.

Not surprised at all after the recent ignition lock debacle. Then there's the cracked dashes on the GMT900 Tahoes.

 

[Hib Halverson]

Anyone have a clue as to what the "machining error" was?

Great write-up!

It's covered in detail in some of the other LS7 content here on the CAC. See this article

 

[Hib Halverson]

Great article Hib and thanks very much for writing it. I have an '08 Z06 with 16,000 miles on it and the valve train sounds as it did when new however, I'm almost afraid to drive it without doing a valve wiggle test. I checked with the owner of a Corvette repair shop in MD and he told me there is no doubt that all '06 through '11 LS7s will eventually have a problem whether you track the car or baby it. His recommendation is to just swap the heads with a new GM set, or well known after market supplier or, he can replace the valve guides in the existing heads, machine them to acceptable tolerances, and rebuild and reinstall the heads. The procedure runs $5K regardless of which route you take. All of the options are better than $10K for a new engine. Frankly, I am completely amazed that GM is aware of the problem and not stepping up to recall the cars. To have a situation that is there fault and in no way caused by or the result of abuse is despicable. I have lost all respect for the company.

If the valvetrain isn't making noise, don't be afraid to drive the car while you wait to have the guide clearance tested.

The guy who told you that all 06-11 LS7 engines will eventually have a problem is vastly distorting the issue, perhaps in the interest of selling you a head repair before you even decide you need it.

First assess wether or not the problem even exists in your engine. Once you do that, then decide on a repair.

 

[Hib Halverson]

(snip)
"it was determined that a machining error in the valve guide had occurred at our head supplier"

Doesn't make sense unless they meant when the guides are reamed?? That being said; industry has gone away from listing processes. Or if the drawing states ±0.007mm with a certain surface finish and the part meets the requirement; no one cares what process was used.

The heads were fully CNC'ed there was no "reaming".

The machining error was that some heads had guide and seat center lines which were non concentric.