Bill Dearborn

Not sure why you would wait with 1.5 years of powertrain coverage. There is a high likelihood the engine wouldn't fail with a couple of HPDEs under its belt. All of the 8 engines that I know that failed had extensive HPDE time as 5 of the 7 drivers are instructors and the other two get a lot of track time but not as much as instructors who go to HPDEs run by many different organizations.

All but one of those engines was covered by GM and when I asked the one guy why he didn't ask them about coverage he thought it would be denied due the usage.

Bill

chadyellowz06

This is very interesting. Thank you for posting this. Here is my theory. As you said the sodium starts to melt at about 200 degrees. Once it liquifies and then the car is shut off and cooled the sodium will dry at either the top or the bottem. My take is the sodium liquifies when this happens the valve gets even hotter as that happens the valve stem expands from the heat then gallows out the inside of the guide. As the guide wears more and more there is not a clean contact patch for the valve stem to transfer heat to the guide into the head and over time breaks.

'06 Quicksilver Z06

I see.

If the OD is still consistent at .313, then it can only mean that the variation in wall thickness occurred during manufacture of the valve.

It didn't wear from the outside. The wall started out thin in some areas from the inside.

This could explain the part number change in May of 2008, and the relative absence of valve breakage in 2009 and up cars.

Bill Dearborn

Quick,
Where did you find evidence of a part number change? My new engine had the same part number as the original engine which was installed in the car in Dec. 07. I would like to believe a change took place but it isn't obvious from the paperwork I have. The new engine was built in May of 11.

Bill

240sx2jz

Quick, i had given my overview of what i thought the manufacturing process was a couple posts back and i definitely think the wall has to do with the concentricity of the tubing to begin with and then gets exacerbated during the final grind. And if they made the change to a better stem stock that would make perfect sense to me. Thats why i wanna see some 2009 valves and section them.

FSTFRC

Airbus keeps saying there was a part number change in 2008 maybe he knows too...

'06 Quicksilver Z06

I have seen you post this before, and I think the confusion lies in which part we are talking about.

There was a part number change for the valves themselves, not engines.

http://forums.corvetteforum.com/c6-z...post1572763145

Dirty Howie

I know this may sound completely outrageous, but just to rule it out can you confirm that:

It is impossible for the liquid sodium at high RPM to errode the inside of the valve stem as you found.


DH

vertC6

Now that I have been able to see the cut away of the stem you really see how hollow and thin the walls really are. I think you have truly discovered a huge piece of the puzzle, comparing this valve with the other one posted yesterday you can see the potential manufacturing flaws. If you get one out of eight exhaust valves that are too thin on one side of the stem that maybe the answer, or at least a big part of it.

It would make sense why some motors go 180k while other blow at 8k, just getting one bad valve coupled with the extreme heat wearing out the guide is all it would take. I not saying 100% this is the answer but I can say with confidence it a big piece of the puzzle. Hopefully you can get your hands on some broken ones and inspect those stems too.

I am excited to see we are getting closer to a true definitive answer to this issue!

FrankTank

Very interesting indeed, I am all eyes/ears will be more interesting as other valves are looked at.

Thanks for taking the time to post all these pics and info

'06 Quicksilver Z06

You could always order a stock brand new valve or even a few of them, and use them for examination.

Part #12618110, can be had from GM parts direct for $28.06 apiece.

'06 Quicksilver Z06

If what you say above does turn out to be true, then part of the currently proposed "fix", the use of heavier stainless steel valves, might not be the best valve option at all.

But rather current updated OEM valves.

It will be interesting to see, but if he slices into several of the newer valves, i.e. part #12618110, and discovers the wall thicknesses to be at or near a consistent .039", then that part of the current recommend "fix" which involves going away from the stock exhaust valves, could take a hit.

Mopar Jimmy

Good point, will be very interesting to see future date on this issue.

chadyellowz06

These are valves and springs that have been sitting around. They have not been cleaned.


Exhaust valves that came out of the 317 high mileage castings. (same heads as in the last video I posted for Bill) As seen in the pictures the valve stems have no significant discoloration or wear considering the mileage. These are staineless steal valves but there is a difference in color of the stem compared to the LS7 stems shown. There is no burnt oil on these.

RamAir972003

Thats because just by guessing without measuring the valves. The oil boiled over its flashpoint to protect. Im guessing...

krackenvette

So, who did GM get their valves from? Seems like they chose poorly. Must have been before the bailout.

vertC6

I would agree with that if I knew 100% that the new valves were truly perfect. Hopefully with more research we find if this is the root cause.

From my perspective I believe like you that throwing a heavy solid SS valve in there is not always the answer. When I look at the stability of the valvetrain my goal is to keep it as light as possible. I plan to use the Katech single beehive that weighs 65 grams instead of a dual spring.

With the release of the 85 gram hollow stem from Ferrea the wall thickness is .080 (twice as thick) but here is the key, I am not comparing it to the weight of the sodium filled but to the Ti intake. The intake is a huge valve and even though it is Ti it still weighs 78 grams, so when you compare it to the much smaller 85 gram hollow stem your not giving up that much in valvetrain stability. If you were constantly going well into the 7500 rpm range then that would be a different story. I plan to set my rev limiter around 7300.

I believe for the majority of guys, who are out of warranty! This would be a good safe fix to the problem.

240sx2jz

I'll have to order a couple of the new part numbers if I cant get them from WCCH...I can't believe they can make this valve for 28$ that is F'ing ridiculous, that's like 1.5 lap dances. Haha....maybe this is the reason there has been variation, the cost doesn't justify QC time??

For me, seeing the thin walls in this valve and the variation in the other immediately turns into differential thermal profiles on all these valves. Which would explain why the tunes have actually had an effect on them. If valve X has a nice even .039 wall versus valve Y at .029 the amount of thermal stress and fatigue They both see is going to be wildly different. Let's hope the new ones had a beefed, more uniform wall. I would still like to see .050 of wall in there, it just seems so thin to be in exhaust temperatures of 1200F-1600F and repeatedly hammered open and snapped shut.

'06 Quicksilver Z06

They changed that part number for one reason or another. Now whether that reason is due to the wall thickness, nobody knows yet, but we might find out soon.

I lot of questions stand to be answered depending on what you find in wall thickness from measurements of random brand new valves.

I am considering buying some of the newer valves myself and cutting into them for measurements.

What are you using to cut them, and with that sodium in them, I know it shouldn't come into contact with water, but what other safety measures are you using when you cut them?

What micrometer are you using to measure the thickness with?

Bill Dearborn

How does GM do part number changes? Everyplace I ever worked when a part of the assembly had its part number changed the next higher assembly/assemblies changed part numbers as well so engineering/manufacturing/field support knew the configuration of the item they were working on. Based on that experience and not knowing how you would keep track of things any other way I assume if the top level part number is the same the complete assembly is the same as assemblies that were produced earlier.

Bill