AirBusPilot

I understand that heat is a byproduct of combustion. You referred to "extreme heat" earlier.

In the above quote, if I am understanding you correctly, you are stating that the LS7's tune, which is rich, still makes too much heat for the exhaust valve.

In the latter part of your paragraph, I believe you are saying that improper clearances won't allow the valve to transfer heat.

I understand the exhaust valve will transfer heat thru the guide and seat. This is normal.

So far, this is what we know:

1. The LS7 tune is rich.
2. Rich tunes mean lower egt.
3. Iron valve guides have been around forever.
4. Stainless sodium filled valves have been around forever.

Based on the above facts, I don't see any reason why the exhaust valve would be experiencing "excessive" or "extreme" heat, meaning heat that is above the design limits of the guide or valve. In fact, the above suggests that the egt's in the LS7 are cooler than optimum.

If out of tolerance valve to guide clearances exist, it is happening one of two ways, IMO:
1. Improperly machined from the factory with excessive clearances. This would be in line with what you are talking about with regard to heat transfer from the valve to the head.
2. Lack of proper lubrication. GM spec oil doesn't have the additives necessary. But, this should be a problem with the entire engine fleet if this is the case. OR, the valve seal isn't allowing enough oil to slip by to lubricate the valve.

Or, we have no idea.

I'm not trying to be argumentative. I'm just trying to clear up some inconsistentcies in what you are stating.

'06 Quicksilver Z06

TJ, in the three incidents you describe, I remember the one where you posted the photos. It was the one you describe had come to you from SoCal.

But the other two, the one which failed on the freeway, and the one which failed during a track day, what were their histories, if you recall?

Also, I believe that you have now added a supercharger to your own car???

What steps have you taken in your own car with regard to the valves, and the valve guides?

Thanks

bgreen83

what are you going to do to keep you valves from dropping. I think this will help slot of people who want some added security for their ls7's.
Thanks

redZ06bri

Very informative if not somewhat disturbing post.

As to the question, "what should one do to protect against this", here is what I've done. (sorry, no mechanical insights or solutions)

1) Bought a 2009 with a 5 year warranty
2) Bought an extended warranty out to 7 years, 72K miles
3) Keeping the car stock so as not to void the warranties
4) Keeping the car off the track, I've kept my indestructo C5 for that
5) After the warranties are done, I'll either have the heads rebuilt or sell the car.

Other than that, I don't see what you can do. It is a known risk with no proven solution, and like it or not, it is clear GM ain't gonna play nice with modded or tracked cars.

By the way, expert opinion from this forum is that the solid steel valves are too heavy for this design.

JMHO

FRDnemesis

I think this is the NEXT direction this post should take.

With all of the Engineering prowess that seems to frequent here, it would be a great public service to those of us who haven't had a failure yet (but are out of warranty) to start planning for some "PREVENTIVE MAINTENANCE".

Speaking for myself, I'm out of warranty and am more than willing to spend some money up front on the cylinder heads than have to replace the entire engine later.

tjwong

The one that failed on the freeway was bone stock, but the owner drove the p**s out of it any chance he got. He also drag raced it, GM denied warranty claiming abuse after seeing lots of tire rubber on the rear quarters.

The track day car was driven hard, that car while basically stock except for suspension mods was a dedicated track car for the owner. So it was driven as hard as can be and more so than most owners here.

My engine has extensive mods to the engine. The heads have the stock iron guides but I went to full roller Yella Terra rocker arms to help reduce friction across the valve tips to help to minimize side load on the stems. I also replaced the exhaust valves with Ferra super alloy valves which is their version of an inconel valve. It is a high temp super duty alloy like iconel but different, well at least according to them because while they call it "super alloy" I don't know the exact name of the actual material that the valve is made of. I have Three engines running these valves and so far not one failure, one I never expect to fail but one is a TT car and the Arab kid that drives it doe USE it and I mean USE it, if you know what I mean.

'06 Quicksilver Z06

If he is in Saudi, Bahrain, UAE, then yeah, I think I know what you mean.

Thanks for the above info.

How much do these valves weigh vs the stock valves?

hoefi

First, let me suggest you go back and re-read my post #148 and #129 three times.

I said the temperature gets too hot for the oil, not the valve or the guide. The valve can survive the heat in the combustion chamber; its stem can certainly survive the heat further away from the combustion chamber. It’s the oil on the stem that can’t survive the heat if the temperature in the stem is too high. Even at rich air fuel ratio, the stem temperature can be really high (much higher than the oil’s cook off point) under WOT if the valve can’t shed enough heat thru the seat. This ability to shed heat is a function of how large the valve head area is relative to the valve seat contact width X the length of the contact strip. Re-read my post #133 (3 times if necessary ) on comments about keeping valve temperature down so that the oil can survive.

We are both talking about oil related failure here. I am saying the primary cause is heat, which broke down the oil. You are saying the valve stem seal prevented the oil getting into the guide. One thing you have to realize is that a valve guide is not a solid chunk of metal with a hole in it. It’s actually a metal matrix with oil entrapped inside a bunch of iron nodules tightly packed together. Think of it as a high-density metal sponge if you like. Yes, part of the lubrication is the oil film on the stem that makes it pass the oil seal. The remaining lubrication is inside the guide itself.

hoefi

There are different types of bronze alloys being used to make guides. Their properties are quite different. Some of the alloys have proven to be less than satisfactory than origially expected. One interesting to note is that Porsches also use iron guides, but Porsche Motorsports uses bronze guides in (some or all???) of their race engines.

hoefi

I believe you are correct and we are talking about the same person.

I haven't practice engineering professionally for quite a while now. I have branched off into other types of businesses but I am still registered as a P.Eng. I would love to design and build race cars full time, but it's a tough way to make a living.

hoefi

Continuation of Part 2:


The local Small Claims Court has a pilot project which requires the two parties to attend a mediation conference. The GM representative (Mr. A) did not attend in person. He attended via a speaker phone. Mr. A confirmed he is an engineer at GM Canada’s head office. GM’s local lawyer (Mr. D) also attended. Up to this point, the only GM live person I got to talk to was the young fellow at the Customer Service call center. At least the lawsuit has now gotten their attention. I opened the conversation by stating the findings regarding the worn guides. That information was first submitted to the dealer, but Mr. A said he didn’t know about that. That didn’t surprise me because GM has been closing smaller dealers down during that period and my dealer was one of them. Knowing what was inevitable with their future, I guess the dealer wasn’t really interested in resolving my problem. Mr. A and Mr. D then went on and said I was racing my vehicle and that’s why the warrantee was denied. That was the first time GM officially confirmed racing was the reason. I then challenged them to show me where in the warrantee documents that says racing will terminate one’s warrantee. I also challenged them where in the documents shows a definition of racing. I have read the warrantee booklet multi times and nowhere does it say that. What it does say is “warrantee does not cover… damages CAUSED by racing….”. This means first we need to determine if driving on the track is considered racing by the court, then GM has to prove that the activity racing caused the engine to fail. In the meantime, GM does not know what caused the engine to fail because nobody from GM engineering has looked at the engine, and their outside engineer did not find the cause of failure either. At some point during the meeting, Mr. A asked me to send him some photos of the engine internal. I refused and told him that the car was at the dealer for three months, they should have taken a look at it then. If he wants to see the engine now he has to get on a plane and come to my house to see it. By that time, I was real upset and I guess I was talking loud. The mediator asked to speak to me privately and eventually convinced me to cooperate. I agreed to send GM some of the photos I have. Mr. A. then asked me to get an outside engineer to certify my report and my findings. I told him if GM wants to pay for the certification cost, I don’t have any objection, otherwise I am stamping my own report. Didn’t surprise me that they didn’t want to pay for MY report.after I said that.


More to come, and I think some of you will be surprised that this forum actually has a major role in this lawsuit.

hoefi

Understood, I will try to put in my 2 cents later. With the latest Canadian $, it might actually worth somehting.

VNAMVET

..........how about a Katech motor...............

My07C6

Subscribing

VicCaerter

This just keeps on getting better and better, like some sort of TV show

forg0tmypen

Oh boy my wet dream!!

AirBusPilot

I've read all your posts. No need to reread. I won't bother, again, to rehash several inconsistent statements and get right to the point.

You keep stating it's a heat related failure, which caused the oil to break down.

I've asked several times "what heat". Meaning, an exhaust valve so hot it destroys the valve guide by exceeding the limits of any oil. Or even an exhaust valve that runs hotter than all the other LS series engines.

Are you stating the LS7 exhaust valve is experiencing excessive heat?

If yes, why?

And/or, are you stating the LS7 exhaust valve has a design problem? If so, what is it?

From what I've read of what you have posted, you are strongly implying the LS7, as an engine, is a total design flaw. And that GM knows this, and purposely runs the A/F rich to compensate. And this over-rich band aid is inadequate to overcome this design problem, the valve is still getting too hot. I think this is a wild assumption with nothing to support it.

This failure has zero to do with air fuel ratio.

forg0tmypen

I hope this is not the case. I don't think GM engineers would let out an engine with such a glaring design flaw. At least I hope...

hapnermw

During low rpm cruise the engine is running in closed loop. This is the engine operating mode with the leanest AFR and is likely the operating mode where the most heat builds up in the valve guide.

I'm told that the top limit of the sodium is low enough that the exhaust valve heat is 'trapped' within the guide. With solid valves the heat is more evenly distributed throughout the valve.

It is the heat concentration in the guide that is likely the cause of the accelerated wear. This is nothing new - many engines with sodium exhaust valves have the same issue.

GM has not said specifically why they chose to use sodium exhaust valves in LS7s and LS9s. It seems clear that on the LS7 they focused on lightening the valve train to support a 7100 rpm redline. So, weight reduction was the likely reason.

Unfortunately, a side effect of this choice is accelerated valve guide wear. GM likely knew this.

What they likely didn't know is the degree to which this wear will result in sodium valve failure.

While there is still some doubt about the second stage of this cause-and-effect relationship, the galling seen on sodium valve stems does seem to be directly related to valve guide wear. And, given the fragility of sodium valves, it seems likely that this galling is an early stage of the failure process.

It is easy to blame modding, tracking and general rude driving for sodium valve failures; however, it is pretty clear that the root cause is the use of sodium exhaust valves.

Regardless of who says 'there is nothing wrong with the sodium exhaust valves' the fact is that in the LS7 they cause the conditions that they are uniquely intolerant off.

If I had an in warrantee unmodded car, I would ask the dealer to remove the heads to verify the valve guides were not worn and offer to pay if all were in spec (which is unlikely if the car has 10K+ miles). Since GM does not replace valve guides, the dealer would have to install new heads. If enough owners did this, perhaps GM would take notice.

'06 Quicksilver Z06

Let me make sure I am following what you are suggesting.

So essentially what you are saying is that if your car has more than 10,000 miles on it, then your valve guides are likely out of spec, and since GM does not replace valve guides, then you would need a new set of heads.

So have the dealer remove your heads and have the valve guides checked to see if all are in spec.

If they are, then you pay the dealer for the labor.

If they are not, then you ask for a new set of heads under warranty?

Whose word do you take as to whether they are in or out of spec?

In a scenario like this, I suspect that most every cylinder head these dealerships remove, they are going to tell you that the valve guides are within spec and the owner is going to end up footing the bill for having his heads removed.

This would be a windfall for dealerships.