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  1. #1
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    Default Valve guide wear on ZO6 427 engine

    I have a 2007 ZO6 with 40000 mi. on it. I haven't experienced any obvious issue with the engine at this point; however, a local Corvette shop has recommended that I have the heads removed and examined to prevent the possibility of major damage to the engine.

    Is this a good idea? Does anyone know how widespread this problem is? Is there any recourse with GM?

    Any recommendations or information would be appreciated.

    TheBugster

  2. #2
    Member TooFast's Avatar
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    All LS7 motors are suspect in regard to the valve guide issue due to potential machining errors from Chevys sub that supplied the heads. The only way to tell you have a problem is to either remove the heads and measure the guides or perform a head in place "wiggle test" to determine if there is a problem. If you read Hib Halverson extensive writing on the LS7 he has a pretty good amount of info on the subject. There are a few good head remanufacturing companies that you can also check out. If you want to read until you cannot read anymore on this subject go the Corvette Forum and there are multiple threads about this.
    Last edited by TooFast; 01-17-17 at 08:30 AM. Reason: Revised matching to machining

  3. #3
    Valve guide wear on ZO6 427 engine Tuna's Avatar
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    Last I heard, if your haven't experienced any valve guide issues by 15,000 miles, you're probably not going to.

    I've got 40K on my 427 and it's still going strong.
    Tuna
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  4. #4
    Member TooFast's Avatar
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    Quote Originally Posted by Tuna View Post
    Last I heard, if your haven't experienced any valve guide issues by 15,000 miles, you're probably not going to.

    I've got 40K on my 427 and it's still going strong.
    Tuna, with all due respect and deference, your experience would not preclude your LS7 from the problem. I would recommend you "wiggle" your valves, especially the exhaust side. 15K miles is no marker for the problem, it has been identified by many after 15K miles.

  5. #5
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    Tuna's engine was built after GM solved the problem.

  6. #6
    Valve guide wear on ZO6 427 engine Tuna's Avatar
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    TooFast: I'm going to leave my engine alone. I don't like doing unnecessary work.

    Hib: When did GM "fix" the 427 valve problem?
    Tuna
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    Likes tomdoesit@gmail liked this post

  7. #7
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    Toofast:
    I'm a former mechanical design type, a GD&T (ANSI Y.14.5-2009 and ISO 1101) guru and stack up analysis type. As my last two prior employers were "global," I was required to be bilingual and "spoke" both ANSI and ISO. Personally I dislike ISO as it has too many "books" and
    ANSI Y.14.5-2009 is one book.

    Stack ups are nothing but a bunch of numbers to say what fits and what doesn't. It goes a lot deeper than my short statement implies.

    AFA, the wiggle test. Consider of two sheets of plastic about .045" thick and separated by 4" and sized exactly .001" larger than a perfectly sized dowel. The dowel is .3761 to .3759 (
    http://www.engineersedge.com/hardware/machine_dowel_pins_chart_ansi_asme__13076.htm)

    Insert the dowel and will it wiggle? I don't think so and the space between the plastic sheets in 4". For a "3/8"" dowel to respond appropriately to a wiggle test the guides would be really shot. GM owes their customers a lot better than a wiggle test. Which will only respond appropriately to certain conditions of detrimental wear, but not all wear. The very, very short form is Corvette owners deserve better than quick and dirty.

    If you disagree, try the math and you'll discover the angularity between the sheets of plastic is very small when the two lines of contact are separated by 4". The less the separation, the less the wiggle. As two circles only have a single line of contact, the wiggle test documents a lot more wear than I'd want in my engine and ignores a lot more wear than we'd appreciate..
    I'm retired or I'd do the math..
    Whoosh, and blur
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  8. #8
    Member LLC5's Avatar
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    Quote Originally Posted by kpic View Post


    Insert the dowel and will it wiggle? I don't think so and the space between the plastic sheets in 4". For a "3/8"" dowel to respond appropriately to a wiggle test the guides would be really shot. GM owes their customers a lot better than a wiggle test. Which will only respond appropriately to certain conditions of detrimental wear, but not all wear. The very, very short form is Corvette owners deserve better than quick and dirty.



    That is one of the reasons GM never validated a "wiggle" test for warranty claims. To determine if a valve guide is worn, the head needs to be disassembled and the valve guide and valve stem measured properly, anything else is just a guess.
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  9. #9
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    Quote Originally Posted by LLC5 View Post
    That is one of the reasons GM never validated a "wiggle" test for warranty claims. To determine if a valve guide is worn, the head needs to be disassembled and the valve guide and valve stem measured properly, anything else is just a guess.
    As a former "numbers" type. I can't say I blame GM. Simply said, it is another internet legend that doesn't work reliably. Reliable means 100% of the time. As my simple example showed, at best, the wiggle test is inaccurate unless the whole valve guide is worn. A simple measurement with a set of ID ball mikes, says nope..

    Measuring properly at the high extremes of accuracy, isn't easy and it is very expensive.. With a valve stem and a guide. At least a Zeiss Contura or Accura.
    As a Master Tech, you might enjoy watching this: CONTURA G2 CMM - YouTube

    It's called metrology and they can measure easily to a whole bunch of zeros to the right of the decimal in millimeter..

    Whoosh, and blur

  10. #10
    Member LLC5's Avatar
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    Quote Originally Posted by kpic View Post
    As a former "numbers" type. I can't say I blame GM. Simply said, it is another internet legend that doesn't work reliably. Reliable means 100% of the time. As my simple example showed, at best, the wiggle test is inaccurate unless the whole valve guide is worn. A simple measurement with a set of ID ball mikes, says nope..

    Measuring properly at the high extremes of accuracy, isn't easy and it is very expensive.. With a valve stem and a guide. At least a Zeiss Contura or Accura.
    As a Master Tech, you might enjoy watching this: CONTURA G2 CMM - YouTube

    It's called metrology and they can measure easily to a whole bunch of zeros to the right of the decimal in millimeter..



    Good video. When repeatability and accuracy are of primary importance, machines are it.

    "Hand built" just doesn't have the same effect (or result) it once had, in fact it's just the opposite now.
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  11. #11
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    Quote Originally Posted by LLC5 View Post
    Good video. When repeatability and accuracy are of primary importance, machines are it.

    "Hand built" just doesn't have the same effect (or result) it once had, in fact it's just the opposite now.
    Today's machines are something special.

    When I got into the business, a dowel's position could be held to less than .012" at a distance of 12" from a center. Position also includes perpendicularity to the mounting surface and rotation or clocking so the mounting holes or threads would align. Today, under .004" is easy. The ease depends on the machine.
    The dowel's perpendicularity at its installed height can be controlled with a projected tolerance zone.

    Your second sentence is "spot on." In the past, balancing turbocharger or supercharger rotors was done by hand, today is quite a different story:
    ► CIMAT Supercharger Balancer with Automatic Drilling (Burke Porter Group) - YouTube

    The balancing is "boringly" accurate, day in, day out and it even vacuums the chips. In the past, chips were removed using high pressure air.

    Assembly is by robots which decrease errors.


    Whoosh, and blur

  12. #12
    Member Iroc2Vette's Avatar
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    So far, I've had no issues with the valve guide wear. I'm quickly closing in on 55Kmi with 4 1/2 years on this car. I also have about 5 hours of track time on it, too. Not hard track. All instructive where I rarely got out of 4rth gear. I've had 2 oil reports, one through Marathon and the last through Blackstone Labs (28Kmi and 45Kmi respectively). The results were extremely good. Blackstone wrote me back stating my engine was wearing less than a 4 cyl Honda with a 2K-3K oil change. I routinely put over 8Kmi on the oil. I do use a very expensive high film strength ester based synthetic oil. My PT warranty is going bye-bye after October 4rth. Then I'll be on my own. I'm not too worried. The engine is also consuming almost no oil, either. It does tick a bit loudly, but, I understand these LS7 engines are a bit more 'talkative' than the other engines. Otherwise, it still walks or runs away from just about anything out there..Sometimes, I don't even have to downshift. Just plant the gas pedal and go WOT
    "Aerodynamics are for people who can't build engines." -Enzo Ferrari

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