95jersey

I have been posting my engine issue in the C6Z forum, but since many of us are using C6Z's these days, I thought I would post my results in the roadrace forum just to document my issue and the potential ongoing valve issues with the LS7.

Long story short, car is my street/track car. I bought her second hand in late 2006 with approx 4k miles. Car now has 15k miles and 20+ track days.

FINAL UPDATE:Car is back home!! Basically, the heads were in VERY bad shape. The valves, guides and springs failed all tests/measurement requirements. Below are the parts that needed to be replaced/upgraded:

OEM valve guides with new bronze guides
OEM valve springs with new springs (OEM)
Stainless Steel Exhaust valve set
All new valve seats/seals
Oxygen Sensors both banks
Spark Plugs
APR head stud kit

This is not the complete list, but you get the idea.

Essentially the only thing salvaged on the heads were the Titanium intake valves (which is good because they are like $800+). The mechanic said the valves were so loose they could be easily rocked back and forth in their respective guides. The exhaust valves themselves were shot and well past any allowable measurement for service. The springs also failed a compression test and needed to be replaced. I had a bad 02 sensor, not sure if it was related, but with all the oil being burned, it most likely was damaged or coated with oil rendering it useless.

Car runs very good now. It sounds very "harmonic" and rev's smoothly. It never realized that it was running on the rough side until I got it back. Also, the car easily passed both a leakdown and compression test. The bottom end is in great condition.

I wanted to document the situation as best as possible for the forum. The car is a 2006 Z06 (Sept 05 build) with approx 15k miles and 20+ track days. The motor is stock except for intake, exhaust and tune. Also, at approx 8k miles a Lingenfelter sump tank was installed. I change the oil every 1500k or 3 track days as I do the rear and tranny (tranny was rebuilt at 7k as 3rd gear blew). I run Hoosier R6 (285/345) on OEM rims with Wilwood BBK and LG coil-overs with T1 bars.

Pumba

Thanks for posting.

While I was at the Corvette World Tribute event at Road America just before Labor Day, one of the other competitors had his 2007 Z06's engine fail.

When he got it back to his dealer, they found that the #8 exhaust valve had failed and the result was everything in the #8 cylinder (piston - rings - etc.) was in the oil pan when the dealer removed the head.

GM replaced his entire engine, dry-sump system, and oil cooler under warranty.

Good luck with your Z.

sothpaw2

Thanks for posting! Just to add to your data...do you tend to shift the car at/near redline for most of your track miles? Or do you tend to short shift most of the time? What was your typical oil temp?

Obviously an LS6 is a whole other beast, but this reminds me that with about the same # of track days, maybe I should be doing my valve springs again.

Glad you found this out in a parade (if I recall correctly) and not on track.

Andy

froggy47

Do you think the engine had a hard life before you bought it, or did all this develop while you were running it?

Any suggestions on how to avoid?

95jersey

Shift points vary, but let's say I don't hold back. I don't purposefully short shift. Oil temps also vary based on ambient, but I usually see 260ish +/-

I don't know for sure what kind of life the car had before I bought it, but it only came with 4k miles and was 100% stock in perfect mint condition and only 1 year old. It ran fine for years after I bought it. I would say this was a result of my hard track days. It didn't make any noise and it didn't seem down on power.

I would have NEVER have known if it wasn't for the parade. To put a smile on some kid's faces, I rev'd the motor in neutral during the parade and that is when the big cloud of blue smoke came out of the tail pipes. After that, I could replicate the smoke every time when the motor had no load.

What was most concerning was the high wear on the valve guides. I could see how one would need to replace springs, but the guides were shot as were the OEM valves.

Outside of telling you to redline the motor in neutral and look for blue smoke, I couldn't give you any other recommendations as to symptoms. Under load the car ran fine.

froggy47

Thanks,

Hmm 20 track days in 5 years is certainly not excessive. Glad it's back to 100%.



GM would like us all to think these motors are ready to run at the limit, but I guess that means a quick trip to the golf course with a couple of bags of clubs in the back. You know, I see these threads from time to time where a forum member testifies how many trouble free track miles they have done with 5w-30 oil and stock cooling & etc. and if you dig a little more it turns out they are mostly parade laps or short shifting & tagging along at the back of the run group or backing off to a cool down lap a few times each session.

Would a leak down test have shown anything in this case? If yes, maybe that shoul be an annual service for all of us. Did your mechanic do this to diagnois?

95jersey

We started with a compression and a leakdown test and if you pass those (which I did) that basically points the issue toward the top end and not the bottom. Also we checked the PVC and intake for any signs of oil residue (meaning smoke could be have been ingested through the intake) but they were bone dry (thanks to an elite catch can).

We could replicate the oil burning consistently in neutral and what also pointed toward the top end was that it would only smoke on the way back down from a full rev (about 2k rpm). It would not smoke on the way up or at the top, just at 2k rpm on it's way back to idle. Apparently, that is a tell tale sign of oil getting past the valve seals vs. oil getting past a bad ring. If oil was getting by the ring, it would smoke more consistently, under load, and through the full range of RPMs.

So based on this we pulled the heads and the rest is history. At least the titanium intake valves did not need to be replaced...$$$!

froggy47

That's a smart tech.

geerookie

Bill was telling me about his same issue this weekend at the Glen.
Apparently there are 30+ of these type of failures documented on this forum alone.

You can see pictures in this thread.

http://forums.corvetteforum.com/auto...s-weekend.html

jamsvet

Thanks for the post. My 06 Z has 34000 miles and about 20 track days. She is under the GMPP warranty and I've talked with the service manager and offered to pay to have them tear it down and check it. He says if it blows up, they'll fix it.

I have coilovers, big brakes and run Hoosier R9s. Engine, trans and rearend are stock but she has a big radiator and Big oil tank. I'm usually in the top three so its not babied.

95jersey

If you have GMPP, I would just wait. Mine ran out.