Help! Buying decision and ‘valve guide wear’ concern – need advice

[EWK]

I am ready to purchase a used 2009 Z06 with only 3,000 miles and then I ran across the dreaded ‘Valve Guide Wear’ thread. The cars warranty is expired and if it develops the problem I will be stuck with the tab to fix it. Is this something that I should be really concerned about and not purchase the car? Is it something that only affected a very small number of owners? What mileage did the failure typically occur? The car is currently in storage and I am set to see the car and inspect it next week, any direction as to how to check out the engine for signs of the problem would be appreciated. I could do the head replacement, any idea as to the cost to rework the heads if the valve guide problem occurs? Your comments would be much appreciated.

 

[Hib Halverson]

It's generally accepted that the cause of rapid valve guide wear in some LS7 engines is a machining error–non-concentricity of the valve guide centerlines and the valve seat centerlines–made by a GM Supplier, Linamar Corp. of Ontario, Canada, on a "small" number of cylinder heads produced between the 2008 and 2011 model years. Linamar was the supplier tasked with the CNC machining of the heads and their assembly. Heads arrived at the PBC fully assembled. No head work was done by engine assemblers.

GM has said the problem was solved in Feb. of MY11.

There is some speculation as to the actual number of defective cylinder heads and there is some speculation that the problem existed as far back as 2006.

I believe the number of bad heads is more than GM would have people believe but I also believe the problem is not "widespread" and affects a minority of the engines built. I'm not sure what to think about the problem occurring in '06 and '07 engines other than to say there is some anecdotal evidence that, in fact, engines built before '08 may be problematic.

It is possible that an engine with only 3000 miles on it may have worn guides if the machining error occurred when that engine's heads were machined. The non-concentricity of guides and seats usually causes rapid valve guide wear. The characteristics of that are a higher than normal level of valve noise and excessive oil use.

When you go to inspect the car, it would be nice to have a known-good LS7 in another Z06 to compare, but that's not practical in many cases. In any event, the engine coolant and oil must be at operating temperature. With the engine idling, any excessive valve noise could be considered a clue that a problem with guides may exist. Of course, the obvious question is: what's "excessive" as far as valve noise from an engine that, when it is in perfect condition, emits a higher level of valve noise than other C6 engines–LS3 and LS9. Lacking another Z06 with a known-good engine, you need to have an ear experienced to listening to an LS7.

As for oil use, since the engine has only 3000 miles on it, as long as the car has not been raced, anything more than half a quart of oil used since new would be reason to use caution.

In the end the only good way to assess the engine's valve guide health is to have the so-called "wiggle test" done on the engine. If any valve in the engine fails, either offer the owner less money or don't buy the car.

Unfortunately, finding a service facility that can do the wiggle test properly may be difficult. There is a lot of inaccurate information on the Internet about the "wiggle test" and there are even some dealers which do not know how to perform the procedure correctly.

Find a dealer with a Corvette tech who knows the procedure and have it done.

Lastly, on a 3000 mile engine, if the problem exists but it's not severe, there's a chance that the wear that's taken place is not "excessive" as defined by the Service Manual. When the wiggle test is performed, on an engine with only 3000 miles, I would be suspicious even of an engine with guide wear inside the "service" spec but outside the "production" spec.

In this case it's almost too bad that the car doesn't have 10,000 miles on it rather than 3000 miles because an LS7 with 10,000 miles and guides which show no excessive wear likely does not have the problem, but an engine with 3000 miles showing noticeable but not excessive guide wear may or may not have the problem.

Good luck.

 

[bill81vette]

Welcome to CAC!!! enjoy!!

 

[EWK]

Thank you Hib

Hib, Thank you for your technical to the point post regarding the valve stem wear problem. It is very much appreciated.

 

[Hib Halverson]

You're welcome. Glad to be of service.

 

[NDAGRUV]

Wil Cooksey LS7

Hib;
Thank you so much for your very informative articles on the LS7! I just read the one here on the website as I too am "concerned" about the possible head issue. I was wondering, my Wil Cooksey Edition #405, was built in April 2008 - is that within the time frame of the questionable valve guide issue?
Some say it was earlier (thus inclusive of mine), and some say it was later.
It currently has 9300 miles on it, NO noise, NO oil loss that I've been able to see (just had the car a short time).
Thanks for your thoughts, and THANKS AGAIN for being such a valuable source of info for the Vette community!!
Curt Ramsey

 

[Hib Halverson]

From 2008 to mid-2011 is the time spread during which the problem which causes rapid valve guide wear to occur.

If your engine is not out of warranty already, it might be soon. I'd pay to have a dealer "wiggle test" the valves for guide wear. If you have worn guides you'll get the heads replaced on warranty. If they find no guide trouble, with 9300 miles on the engine already, you're likely ok.