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

Corvette forums are always full of chatter about possible engine problems. In recent years, a lot of information—and misinformation—has been floating around about what C6 or Z06 Corvette owners should know about a common issue with the LS7 engine valve guides. Here, we break down what is afflicting these V8s, how many engines might be affected, and how to tell if your LS7 suffers from it.

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What Corvettes are Affected?

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, and GM narrowed the issue down to Corvettes built between 2008 and 2011—roughly less than 10 percent of Z06 models. 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

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GM 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.

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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, according to 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'?

The "Wiggle Test" is a nickname for a procedure believed to diagnose valve guide wear. It supposedly measures the valve-to-stem-guide clearance accurately without first removing the heads, a labor-intensive process.

Though the test has been 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 the results. Through this imprecise procedure, some Corvette owners have mistakenly diagnosed worn valve guides when no issue existed.

Automotive writer Hib Halverson had previously advocated for this test. He retracted his recommendation in a March 2015 post on a popular Corvette forum:

"'Wiggle Testing' at best is inaccurate and in many cases is completely unreliable. 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

The LS7's valve guide problem is a perfect example of how of incorrect information, spread on the internet, can lead to over exaggeration and inaccurate diagnosis procedures. 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.

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3 Things to Check If You Suspect LS7 Engine Problems

2006 7.0L V-8 (LS7) for Chevrolet Corvette Z06 — 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.

What does your engine sound like? According to GM, the most common customer complaint has been excessive valve train noise. 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.
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.
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.