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

Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 36
  1. #16
    New Member
    Join Date
    Mar 2004
    Location
    Charlottesville, VA
    Posts
    8
    Corvette(s)
    2008 Z06
    Post Thanks / Like
    Rides
    0

    Default Wiggle Test

    Quote Originally Posted by LLC5 View Post
    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.
    Last edited by megavettes; 12-23-14 at 10:38 PM.

  2. #17
    Member 73shark's Avatar
    Join Date
    Jun 2007
    Location
    KC, MO area
    Posts
    603
    Corvette(s)
    1973 Orange Metallic L-82 Coupe
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by megavettes View Post
    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.
    Save the wave

  3. #18
    Technical Writer for Internet & Print Media
    Join Date
    Jan 2001
    Location
    CenCoast CA
    Posts
    11,952
    Corvette(s)
    71 04 12 19
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by 73shark View Post
    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

  4. #19
    Technical Writer for Internet & Print Media
    Join Date
    Jan 2001
    Location
    CenCoast CA
    Posts
    11,952
    Corvette(s)
    71 04 12 19
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by megavettes View Post
    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.

  5. #20
    Technical Writer for Internet & Print Media
    Join Date
    Jan 2001
    Location
    CenCoast CA
    Posts
    11,952
    Corvette(s)
    71 04 12 19
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by kpic View Post
    (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.
    Hib Halverson

  6. #21
    Member 73shark's Avatar
    Join Date
    Jun 2007
    Location
    KC, MO area
    Posts
    603
    Corvette(s)
    1973 Orange Metallic L-82 Coupe
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by Hib Halverson View Post

    The machining error was that some heads had guide and seat center lines which were non concentric.
    That'll do it. Thanks, that saved reading the 23 pages of that other thread to find it.
    Save the wave

  7. #22
    New Member
    Join Date
    Mar 2004
    Location
    Charlottesville, VA
    Posts
    8
    Corvette(s)
    2008 Z06
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by Hib Halverson View Post
    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.
    Thanks Hib. I'll certainly take your advice and check it first.

  8. #23
    Member
    Join Date
    Mar 2014
    Location
    Columbus, NC/NE Georgia
    Posts
    2,293
    Corvette(s)
    1997 boosted silver coupe
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by Hib Halverson View Post
    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.

    Hib,
    As I said, reaming is an old term. Today all we care about is holding the required value and proving capability. Years ago, production drawings would say drill to X and ream; that is no longer true. Reaming is a process and Design could give a hoot if the bore is reamed or cut with a single point tool. Surface finish is another story.

    Cpk is the measure of process capability and requires the process to be centered.
    If anyone is interested: Process Capability (Cp, Cpk) and Process Performance (Pp, Ppk) – What is the Difference?

    With a valve guide concentricity means the OD is centered within an allowable error to the ID.

    So what is concentricity: GD&T Concentricity Definition | eMachineShop

    What the picture means is the ø25 ±0.05 with be centered on Datum A within a diametral zone of 0.05. No matter if the bore is ø25.05 or ø24.95 there is no bonus tolerance which means no movement based on size deviation.

    This is bonus tolerance: Untitled Page

    As checking concentricity requires a median of points which means a gage doesn't work. Short form, it is expensive to check.Usually, automotive is more prone to use position tolerance; aerospace uses concentricity.

    If you take two pieces of round stock and drill a hole in both. If both bores are .0015" larger than the mating piece; no matter if it is centered or off center from the OD there will be no difference in wiggle. That is just the nature of fits. There is no difference between .0015" of clearance and .0015" of clearance. Wiggle would be induced by a size, taper or other factors, but not a concentricity error

    Sorry, it might be some placebo floating around but, the concentricity boat don't float. Can anyone guess what I do 8 hours a day..
    Whoosh, and blur

  9. #24
    Member LLC5's Avatar
    Join Date
    Sep 2004
    Location
    Wa.
    Posts
    2,299
    Corvette(s)
    98 black 6spd convert.
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by kpic View Post
    Hib,
    As I said, reaming is an old term. Today all we care about is holding the required value and proving capability. Years ago, production drawings would say drill to X and ream; that is no longer true. Reaming is a process and Design could give a hoot if the bore is reamed or cut with a single point tool. Surface finish is another story.

    Cpk is the measure of process capability and requires the process to be centered.
    If anyone is interested: Process Capability (Cp, Cpk) and Process Performance (Pp, Ppk) – What is the Difference?

    With a valve guide concentricity means the OD is centered within an allowable error to the ID.

    So what is concentricity: GD&T Concentricity Definition | eMachineShop

    What the picture means is the ø25 ±0.05 with be centered on Datum A within a diametral zone of 0.05. No matter if the bore is ø25.05 or ø24.95 there is no bonus tolerance which means no movement based on size deviation.

    This is bonus tolerance: Untitled Page

    As checking concentricity requires a median of points which means a gage doesn't work. Short form, it is expensive to check.Usually, automotive is more prone to use position tolerance; aerospace uses concentricity.

    If you take two pieces of round stock and drill a hole in both. If both bores are .0015" larger than the mating piece; no matter if it is centered or off center from the OD there will be no difference in wiggle. That is just the nature of fits. There is no difference between .0015" of clearance and .0015" of clearance. Wiggle would be induced by a size, taper or other factors, but not a concentricity error

    Sorry, it might be some placebo floating around but, the concentricity boat don't float. Can anyone guess what I do 8 hours a day..


    If I had only on guess, it would be Boeing Engineer.
    Master Technician

    25+ year ASE Master Certified Tech

    22+ year Honda Master Tech

  10. #25
    Member
    Join Date
    Mar 2014
    Location
    Columbus, NC/NE Georgia
    Posts
    2,293
    Corvette(s)
    1997 boosted silver coupe
    Post Thanks / Like
    Rides
    0

    Default

    Dinner is over..

    Quote Originally Posted by Hib Halverson View Post
    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.
    As a CNC can do rough bores, finish bores and even the fancy cylinder bore crosshatch finish; if needed a ream can be mounted in a tool holder. When this is done, the ream removes an extremely small amount of material; however, it does yield a very nice surface finish.

    Typically a CNC (computer numeric control) or a computer controlled machining center has a limited number of tool holders. To reduce tolerance and tool holders usage; profile tools are used. A profile tool is a combination tool. The slang name for best example is a Parker tool which cuts every feature of an O-ring port in one operation.

    Where I used to work; the guide bore and the valve seat bore were cut in one operation by one tool. Profile tools which cut multiple features in one operation significantly reduce tolerance as a profile tool cuts a bunch of features in one operation and is built to tool maker's tolerances; not production tolerances.

    The seats were pressed and cut using the guide bore as the locator. It depends on the OEM if the seats are cut; they can easily be already cut and simply pressed in.
    Potentially, offsetting the seat bore to the guide bore could cause wiggle after XXXX cycles by wearing the guide bore. However, just as easy, it would cause the valve to bind or gall due to induced angularity. The next valve opening cycle would cause a catastrophic failure.

    As we don't have access to GM's FMEA (Failure Mode Effects Analysis) we will never know the real reason or reasons. Point is the boat still don't float.
    Whoosh, and blur

  11. #26
    Member
    Join Date
    Mar 2014
    Location
    Columbus, NC/NE Georgia
    Posts
    2,293
    Corvette(s)
    1997 boosted silver coupe
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by LLC5 View Post
    If I had only on guess, it would be Boeing Engineer.
    LOL, no Sir. I'm a hill billy power train designer. Automotive is and has been my love and I was fortunate to work in vertically integrated businesses. Where I saw the processes instead of offshore.
    Except for the last 10 years; Class 8 engines (I6 and V8), transmissions, differentials and transfer cases. I've been in Design Engineering since 1970.

    After I retire, I'll own up to where I work now. I enjoy where I am now because most of the staff enjoys high performance vehicles, classic cars, muscle cars, auto crossing and more. They understand why I added a centrifugal to my Corvette.
    Whoosh, and blur

  12. #27
    Technical Writer for Internet & Print Media
    Join Date
    Jan 2001
    Location
    CenCoast CA
    Posts
    11,952
    Corvette(s)
    71 04 12 19
    Post Thanks / Like
    Rides
    0

    Default

    (sigh)

    All this bandwidth expended on "concentricity".

    Here's the 411:

    If the centerline of the guide bore and the CL of the valve seat are not concentric, as the valve hits the seat, it's pushed sideways. That wears the guide. How quickly the guide wears depends on how great the non-concentricity.

    In an LS7 head, concentricity is very simple to measure with a tool like this.

    I have measured numerous LS7 valve seats with that tool and found up to .005-in non-concentricity on new and used cylinder heads. The factory limit is .002. Someone really good with a Serdi should be able to hold it under .001-in.

    The other way to measure concentricity, and how GM Powertrain does it is with a CMM...clearly a bit more accuracy is involved with that but, in the field, the a seat runout gauge is sufficient.

    Merry Christmas, everyone

  13. #28
    Technical Writer for Internet & Print Media
    Join Date
    Jan 2001
    Location
    CenCoast CA
    Posts
    11,952
    Corvette(s)
    71 04 12 19
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by 7thz16 View Post

    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.
    General Motors has never stated that LS7 owners should have engines inspected for valve-stem-to-guide clearance at 10,000 miles. The Corvette Action Center, based on our research into the LS7 valve guide problem, makes that suggestion. if you are a C6 Z06 owner concerned about guide wear, but your engine is not demonstrating any signs of the problem, if the engine has 10,000 miles or more on it; do a wiggle test. If the engine passes, it does not have the problem and, as long as the engine's valvetrain is not modified and the engine is not subjected to frequent severe duty cycles, it likely will never experience premature valve guide wear. If the engine flunks, have it repaired.

    In fact, there have been a few cases of excessive guide wear, even valve failures due to guide wear, in engines with far less than 10,000 miles on them. Some of those cases may have demonstrated obvious symptoms, such as excessive valve noise, high oil consumption or the MIL on due to misfire. Even though the symptoms might preclude some from measuring all 16 valves' stem clearance, proper diagnosis is going to require wiggle testing several of them.

    An engine can have excessive guide wear and not demonstrate any of the above symptoms. Its those engines that the "wiggle test at 10,000 miles" is intended to detect.

    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.
    CAC's research indicates that GM understated the amount of model years in which the problem can occur.

    This guide wear problem is not widespread–there are many LS7s with a lot more than 10,000 miles on them which have no worn guides–but it is a documented problem which has affected some engines and it's affected some outside the model year range GM has stated publicly. We proved that with during the research for the revision of the CAC's main LS7 article.

    If it occurs, in its early stages, it will not cause any of the symptoms discussed in the Jan. 2013 Information Service Bulletin covering the problem. Again, our recommendation to wiggle test at 10,000 miles is directed at those who are concerned about the problem but have an LS7 that's not showing those symptoms, i.e.: no excessive valve noise, no excessive oil use or no MIL. Obviously, if your engine currently demonstrates those symptoms, you need to get the engine repaired rather than just checking valve stem clearances.

    Happy New Year, all!
    Last edited by Hib Halverson; 01-04-15 at 01:59 PM. Reason: revised and restated content

  14. #29
    Technical Advisor c4c5specialist's Avatar
    Join Date
    May 2001
    Location
    New Haven, Ct. USA
    Posts
    3,682
    Corvette(s)
    Nope, but someday.
    Post Thanks / Like
    Rides
    0

    Default

    This is now where I get involved because now you are talking complete speculation!

    This quote is absolutely assumptive.

    In fact, there have been some cases of premature guide wear in engines with far less than 10,000 miles on them, but those engines demonstrated symptoms, such as excessive valve noise, high oil consumption or the MIL on due to misfire. Obviously, a wiggle test in those situations is unnecessary because it will only tell you what you already know: the guides are worn.

    2006-15, yes I am including LS7 in Camaro, there are over 250 different causes for misfires, MIL or other factors.

    I have had over 50, yes 50 LS7 apart, and to make the assumption that all these engines had issues with the valve guides is false.

    ACCURATE DIAGNOSTIC PROCEDURE, NO MATTER ON WHAT ENGINE MUST BE FOLLOWED. Mileage varied between 11,200 and 166,341 on the LS7 I have served. 3 had valve guide issues.

    Assumption is a luxury that professional GM service technicians NEVER HAVE.

    3 out of over 50, hm, not too bad of an average.

    But I will NEVER EVER EVER GUESS that an engine, LS7 or others have these issues.

    EACH engine must be measured, correctly tolerance checked on its own merits of diagnostic procedure.

    Allthebest, Paul


    Last edited by c4c5specialist; 01-02-15 at 12:43 PM.
    GM World Class Certified Technician.
    Like us: www.facebook.com/corvettemechanic
    http://twitter.com/GMvettemechanic
    http://thecorvettemechanic.com
    Podcast: Itunes, search 'the corvette mechanic'
    Likes dougelam liked this post

  15. #30
    Member dougelam's Avatar
    Join Date
    Jul 2011
    Location
    Michigan
    Posts
    449
    Corvette(s)
    2002 Roadster
    Post Thanks / Like
    Rides
    0

    Default

    Quote Originally Posted by c4c5specialist View Post
    This is now where I get involved because now you are talking complete speculation!

    This quote is absolutely assumptive.

    In fact, there have been some cases of premature guide wear in engines with far less than 10,000 miles on them, but those engines demonstrated symptoms, such as excessive valve noise, high oil consumption or the MIL on due to misfire. Obviously, a wiggle test in those situations is unnecessary because it will only tell you what you already know: the guides are worn.

    2006-15, yes I am including LS7 in Camaro, there are over 250 different causes for misfires, MIL or other factors.

    I have had over 50, yes 50 LS7 apart, and to make the assumption that all these engines had issues with the valve guides is false.

    ACCURATE DIAGNOSTIC PROCEDURE, NO MATTER ON WHAT ENGINE MUST BE FOLLOWED. Mileage varied between 11,200 and 166,341 on the LS7 I have served. 3 had valve guide issues.

    Assumption is a luxury that professional GM service technicians NEVER HAVE.

    3 out of over 50, hm, not too bad of an average.

    But I will NEVER EVER EVER GUESS that an engine, LS7 or others have these issues.

    EACH engine must be measured, correctly tolerance checked on its own merits of diagnostic procedure.

    Allthebest, Paul


    Well put Paul
    The 3.6L in our Enclave has a known problem with water pumps, should I remove it and wiggle the impeller to see if it is going to fail someday?

    If there is a symptom check it out
    If not don't worry about you will only lose sleep over spilled milk

    2002 W/Borla Exhaust

Page 2 of 3 FirstFirst 123 LastLast

Similar Threads

  1. Valve stem seals (again!)
    By boblx2a in forum C4 Technical and Performance
    Replies: 7
    Last Post: 10-04-06, 07:59 PM
  2. Valve Stem Question
    By hcolon in forum C5 General Discussion
    Replies: 8
    Last Post: 07-18-06, 09:17 PM
  3. Valve stem
    By bling vette in forum C6 General Discussion
    Replies: 8
    Last Post: 04-26-06, 11:54 AM
  4. Valve stem
    By bling vette in forum C5 General Discussion
    Replies: 1
    Last Post: 02-18-06, 06:33 PM
  5. Valve stem caps
    By TheLabattMan in forum C5 Technical and Performance
    Replies: 2
    Last Post: 06-26-02, 12:03 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •