dmuellenberg

I had to read this a couple of times since it confused me. Saying something is a huge stretch (at least to me) means that it is an over exaggeration (stretch meaning to make something bigger/longer). But from the examples you pointed out, I'm assuming that you meant an underestimation.

dmuellenberg

I guess I take some offense to that. Just because I use mine as a daily driver doesn't mean I drive it like an old woman.

EWK

I am the lucky or unlucky owner of the 2009 Z06 who is represented in the report that Jason posted. I purchased the car in April with only 3,021 miles on it and in pristine condition. I have been following the valve guide wear issue since my purchase and the more I read, I decided to address the problem now rather than later and I contacted Jason at Katech. I happen to live about an hour drive from Katech Performance and made an appointment with Jason to discuss the valve guide issue in more detail and tour the Katech Performance facility. I was totally blown away with the overall size of the facility and the number of departments it contains. The other thing that sold me was that every area of the facility was organized and looked like a clean room. Also, being that the racing season was over for the year I was able to get the car into the shop right away and was very comfortable with the mechanic assigned to do the work. When I picked the car up after the work was completed, it was impossible to tell that the heads had been removed, reworked, and reassembled except for a noticeable decrease in the valve train noise level from the engine. This is a heads up for Jason, the mechanic that worked on my car and Katech Performance in general.

Unreal

3% is way way way low. All the local shops see the same thing, it is very rare to find one in spec compared to out. I would say 3% in spec is more accurate than 3% out.

Dirty Howie

And a couple of my track buddies with almost the exact number of street miles and track hours failed the wiggle test on their OEM heads/motors.


DH

[Cerberus]

Readings like this make me wonder what exactly the tolerance was when they were new.





Sodium has better thermal conductivity than either Titianium or Stainless steel. The sodium will wick heat away from the valve seat faster than a solid Ti or Stainless valve.

cdavekirk

You got it! GM can spew all the hype they like about the C7Z06. They did it with the C6Z06 too. Bottom line anybody that denies there is a problem and anybody that feels that GM would never screw owners like this on the C7 is a fool. Absolutely disgraceful...

DON T.

Good for you! I guess im glad i do not live an hour away from Katech, i would never be home Also the same when recieved my Z back, Clean and spotless everywhere.

JKLNHDE

Please re-read my post - i said nothing about THE driver/owner of the car or attempted to imply it was the fault of THE cars driver. I was inquiring as to whether the car was essentially a high rpm track/race car or an easy going [daily] driver to get a feel for the engines history. Big difference in interpretation - I wasnt pointed any fingers you misunderstood.

Turbotank

Did you check yours? I had 69k on mine and the drivetrain was as quite as any LS engine i've had but my exhaust and intake valves were WAY out! One of my intake valves couldn't even be reused....

dmuellenberg

I'm going to have them measured when they work on the heads. All I was pointing out was that not every Z06 has the same rate of guide wear as his. If that was the case, then there wouldn't be any 100k stock engines out there, which of course there are.

99SoCalFRC

So what does Katech or any other vendor do different than GM? You can't change the geometry of the head, nor does anyone suggest a roller rocker is needed to prevent future issues.

So what about the aftermarket machining/ guides creates a belief that the heads are now better than OEM? I'm asking because I really don't know and I want someone to tell me. Does Katech or anyone else remeasure the guides after years of driving on their heads?

Random84

if you allow for the possibility that the heads were out of spec from ASSEMBLY, and that the reason we're seeing such sporadic "wear" mixed between both intake and exhaust guides even on the same engines (some cars have intakes way out, some have exhaust guides way out, some have both - with a wide range of mileage when owners open them up); you might understand that "The Fix" is nothing more than competent head machining and assembly so that the guides and valves are set up properly from the get-go.

Remember that these heads were sourced by suppliers and not assembled at Bowling Green; so the head geometry and tolerances are at the mercy of the subcontractor. These aftermarket shops all have valid approaches for various valve, guide and spring choices - but the unifying theme of success is getting back to basics: ensuring the valves and guides have proper clearances for lubrication and heat transfer.

if some of the guides were machined improperly from the get-go, it explains everything that we're currently seeing. IF it were just heat transfer and "bad valves" then we wouldn't see crazy Intake "wear" OR crazy exhaust valve "wear" on cars that are barely out of the break-in period.

Katech_Zach

We repaired the guide concentricity issue by installing new bronze guides and doing a valve job. Changing the rocker arms is not necessary.

We have had our customers bring back race engines for rebuild that have bronze guides and Ti/Mo valves installed. Guides were re-measured and found to be holding up very well.

Mig233

Hmmmm, so the problem can be traced to suppliers? Interesting. So it is a defect in the valve guide material (Powdered Metal)? Or is it a geometry issue?

Katech_Zach

It's a machining issue traced to the supplier of LS7/LS9 heads, Linamar.

Bill Dearborn

Since most production level machining nowadays is performed on computer controlled machines that indicates there might be a maintenance issue with a machine or an issue with the control program for the machine/machines. They could conceivably have two programs one that is correct and one that is incorrect with the same P/N applied to each. Since not all heads have the problem it looks like there is some sort of QC problem with the machines or the control programming. GM said the problem was resolved on their end by doing a complete incoming inspection on heads delivered after Feb. 2011. It would be interesting to see how the results vary in heads that were delivered to GM after that time.


Bill

Mig233

What exactly is the machining issue? Valve guide angle? Valve guide bore? Or something different?

I thought I read about some 2013s blowing up due to valves dropping. I'm not sure if any of the new Z28s have had issues yet.

jedblanks

Finally. The real answer to this whole fiasco.

Unreal

I would bet money it isn't a programming issue. Automotive tools are all IQ/OQ/PQ'd typically. I would say if anything it is a PM, wear, tooling, etc issue. Tolerance stack up, CPK of the machining process, etc.