Corvettes Owners: LS7 Engine Problems and the 'Wiggle Test'

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Corvette LS7 Worn Valve Guides

2006 Corvette Z06
2006 Corvette Z06. (Photo by Auto BILD Syndication/ullstein bild via Getty Images).

There is a profuse amount of chatter across Internet forums and throughout Corvette shows about problems with LS7 engine valve guides. But what exactly is afflicting these V8s, how many engines are affected and how do you know if your LS7 suffers from it? We break down what every C6 Corvette owner needs to know about the LS7 issue.

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What Corvettes are Affected?

2006 Chevrolet Corvette Z06. Photo courtesy of General Motors.

The valve guide problem pertains to the LS7 engine, which was installed on C6 Corvette Z06 models from 2006 to 2013. But not all Z06 Corvettes from the sixth generation are affected, with GM narrowing the issue down to Corvettes built between 2008 and 2011. The manufacturer has not released an accurate tally of affected engines but it has been predicted that less than 10 percent of Z06s have this problem. Going off the production numbers from 2008 to 2011, it's safe to estimate that less than 1,300 Corvettes may have the issue.

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What the Problem Is

Cylinder head
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GM has traced the problem back to one of its cylinder head suppliers. By analyzing heads returned under warranty, it was discovered that some weren't machined properly. On these LS7s, the valve guides and valve seats weren't concentric, which led to severe wear of the valve guides.

SEE ALSO: Corvette Owners Sue Chevrolet Over LS7 Engine Problems

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What the Problem Isn't

Bloomington Gold Corvettes Indianapolis
Corvettes line the Indianapolis Motor Speedway for Bloomington Gold. Sarah Shelton

This is a not a widespread mistake that applies to all 28,000 Z06 Corvettes from the sixth generation, says GM. The carmaker believes that much of the hype relating to LS7 valve guide wear has been the result of misinformation, and was not based on the insubstantial number of engines returned under warranty. Mechanics familiar with the worn valve guides on the LS7 agree, noting that only a very small percentage of Corvettes have been found with an incorrectly machined cylinder head from the factory.

Corvette owners should also be cautious about lumping any modified Corvette in with the problem LS7s. Some aftermarket parts have not been developed to be in tune with the Corvette engine, or may have a conflict with other performance upgrades. If an LS7 with high performance modifications has worn valve guides, it's more likely to be the result of the add-on components than an issue with poorly machined cylinder heads. 

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What's the 'Wiggle Test'?

Mechanic auto repair
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The "Wiggle Test" is a nickname given to a procedure to diagnose valve guide wear. It supposedly could measure the valve to stem guide clearance accurately without first removing the heads, a labor-intensive process.

Though the test was hailed as an easy way to identify worn valve guides, the Wiggle Test is actually a poor method to use because it doesn't factor in several variables that will throw off results. Through this imprecise procedure, some Corvette owners have mistakenly diagnosed worn valve guides when no issue existed.

Even one automotive writer that had previously advocated for this test has since retracted his recommendation:

"'Wiggle Testing' at best is inaccurate and in many cases is completely unreliable," said Hib Halverson. "Observing one of my heads being measured by one of GM's Zeiss CMMs proved to me conclusively that even the complicated and careful procedure I covered in my Wiggle Test article produces data which is inaccurate and inconsistent such that, unless the clearance measured is significantly greater than the Service Limit of .0037-inch, the measurements are useless for determining if a head needs repair or replacement due to valve guide wear.

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Read Forums With Caution

Man reading computer screen
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Owner forums can be a great way to connect with Corvette enthusiasts across the country. And they can also be a great resource. But they should be used with caution to definitively diagnose a problem or seek out mechanical advice. While there are certainly many knowledgeable people that contribute to forums, it is often difficult to discern the experts from "shade-tree" mechanics. This can easily lead to misinformation, which then spreads like wildfire.

Problems over LS7's valve guides are a perfect example of incorrect information on the Internet that has led to an overexaggeration of the problem and inaccurate diagnosis procedures.  

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3 Things to Check If You Suspect LS7 Engine Problems

2006 7.0L V-8 (LS7) for Chevrolet Corvette Z06. Photo courtesy of General Motors.

Do you suspect that your LS7 is having issues? Start by checking these three areas first before disassembling the engine or getting an expensive diagnosis.

  1. What does your engine sound like? "The most common customer complaint has been excessive valve train noise," according to a Chevrolet representative. If you aren't sure if your engine noise is normal, Corvette mechanic Paul Koerner recommends finding a Z06 with an LS7 and similar miles and comparing the two engine sounds with the cars side by side.
  2. Are you using too much engine oil? If you are using more than one quart of oil for every 2,000 miles -- the normal oil usage for the LS7 -- then an underlying problem exists. You can also remove a spark plug to see if the end has been fouled from excess oil consumption.
  3. Is your check engine light on? The vast majority of the time, an issue within the engine's valve train will result in a check engine light.

After checking these three items, if you suspect that your Corvette has an engine issue, seek out a mechanic who is experienced with this specific engine. With its unique architecture, the LS7 is tuned in a different way than the LS3, the base engine for C6, and the C6 ZR1's LS9.

* A special thanks to Paul Koerner, GM World Class Certified Technician and resident expert at The Corvette Mechanic