propain

Presumption.

As is his statement on heat problem with running hollow valves minus the sodium. Not a bad one but the proof is in the pudding. We have spent years on this forum hypothesizing this problem. From "There is nothing wrong" to "The valves are the devil" and everything in between.

The ZR1 that just reported having worn out guides in 900 miles no way in hell had worn out guides from the above hypothesis. As well we have intake guides completely out of spec while the exhausts remain fine.

Entities should not be multiplied unnecessarily. The heads have come out of the GM supplier with machining issues along with terrible QC and have led us to where we are today. While I do love a good debate many people are over thinking this.

Undy

Once the guide starts to wear and the valve stem moves radially an excessive amount in the guide then the stem seal will lose control of its sealing duties and permit oil to enter.

propain

Wouldn't this lead to excessive oil consumption? With these failures and inspections with worn out guides most if not all have reported no oil consumption issues.

Do you think the oil consumption from this issue would be so minimal it would go unnoticed?

ticat928

I recall 2-members having observed going from no oil consumption to 1/2 a quart in the last 300-500 miles prior to dropped valve.

Since this cascade failure proceeds at such a rapid pace; 99% of the members do not have the fortune or premonition to check oil level just ahead of dropped valve event.

Once you start to see the oil level go down all of sudden it is time to do wiggle test ahead of anymore driving.

ticat928

"10-22-2014, 03:09 PM #2767
Hib Halverson
CF Senior Member


(Quote):
Originally Posted by '06 Quicksilver Z06 View Post
Thinking back to Hib's posts regarding the air filled hollow stemmed Ferrea valves and inadequate heat transfer, I started wondering if there are any auto manufacturers out there who run such a valve in their vehicles.
While I have been able to find examples of solid stainless valves, even sodium filled hollow stemmed valves in vehicles made by GM, Ford, Dodge, Ferrari, etc., I have been unable to find any examples of engines built with air filled hollow stemmed exhaust valves.
Does anyone know of any manufacturer which builds it's engines using such an exhaust valve?
Thanks (Quote)


My research did not find any mfg. which has engines with hollow-stem, air-filled valves, either.

I see a lot of other questions driven by some stuff I posted a day or so ago. We're on deadline with the first part of the big revision to the CAC's LS7 article. I'm really pulling a lot of OT on that and won't be able to answer some of the questions you guys have asked for several days."

Per Hib's post above I think he will be pleased you Guys are doing some critical thinking and asking questions, keep it up.


"10-21-2014, 04:18 PM #2742
Hib Halverson
CF Senior Member

(Quote):
Originally Posted by propain View Post
I understand the reasons Hib. I have seen you make this assertion before as well. I would like to see anything you have on the negative impacts of running hollow valves minus the sodium in the LS7 head. I am sure the forum would appreciate it too. What are your predictions? More worn out guides?(Ouote)

My predictions, given a hollow-stem, "air-filled" valve.

If the seats and guides are improperly machined such that they lack concentricity, accelerated guide wear will occur. As that rapid wear occurs, the heat transfer path will be quickly degraded. Then, the wear rate will not only accelerate, but the rate of that acceleration will, also, accelerate and the guide will wear really fast. As the guide wears, PM particles will form an abrasive slurry with the oil. The heat will turn that slurry to an abrasive coke. You can guess the results.

If the seats and guides are properly machined, guide wear will start much more slowly because it will take a while for the degrading heat transfer path between the stem and guide to get to the tipping point where guide wear "snowballs" and oil coking begins to contribute to the coming catastrophe. If you used an mPAO- or ester-based synthetic and stem sealing was less aggressive and the duty cycle was not severe, you might be able to conteract the problem.

With exhaust valves, in general, there are two main paths for cooling:
1) valve face, to valve seat, to head material, to coolant
2) valve stem, to valve guide, to head material, to coolant. Keep in mind that for this to occur, the stem has to be very close to or touching the guide.

There has to be some proportion between 1 and 2 and the magnitude of each depends on many different design factors.

My belief is the LS7 exhaust cools less by #1 than do other engines because there is no coolant around the valve bridge and that bridge is so small. It follows that the LS7 exhaust cools more by #2 than do other engines because it cools less through #1.

If the above is true, it follows that the condition of the stem-and-guide "system" is more important than with other engines because more of the valve cooling load falls on that guide.

My theory is that the LS7 is more sensitive to exhaust valve cooling though the guides and, as a result, when guide wear occurs, depriving the valve of some of its cooling–and cooling though the seat cannot pick-up the slack–once that guide starts to wear, the valve stem runs hot, the wear rate snowballs, the heat gets hotter and the oil starts to coke. Finally there’s some kind of failure.

Another of my beliefs is that, given guides and seats which are concentric, and rocker pivots and guide centerlines which have the correct separation, then stock LS7 exhausts work well up to the 575-600-hp level provided that PM guides are used, an mPAO (Gibbs Driven) or ester-based (Red Line) 10W30 engine oil is used and any PCM "tuning" done is very limited when it comes to leaning the engine at WOT to make a little more power.

Let it be known that when my heads were replaced under warranty at 16,034 miles, it was solely because of intake guide failures and intake valve seat runout. There was no problem with exhaust guides or exhaust valves. I'm still asking myself: if the stock exhaust was such a POS, then why did they not fail in this instance? In fact, had GM not replaced the heads, I could have repaired the intake guides and seats and kept the original exhaust guides and valves. When we measured the new heads, I was astonished to find that one of them (which became the right head) had some stem-to-guide clearances which were incrementally greater than in the used heads we removed. Go f**king figure!

If it were my engine and I wanted 600+hp, I'd consider either an Inconel exhaust with an appropriate change in valve spring pressure or I'd use a titanium exhaust."

Hib's original post above contains a lot of intelligent theory's for our consideration and questioning, when he comes back I am sure you all will be marked on how well you did your home work LOL.

Undy

One would think so in extreme conditions. Evidently the seals are very compliant to excessive radial movement of the valve stem.

I had similar guide problems with a SBC I had in a Datsun 240Z back in the 70s. The guides had to be VERY bad before I saw significant oil consumption.

I would think that it shouldn't take too much oil in the guide to make a slurry, just enough to act as a bonding agent for the PM guide particles.

propain

I had a similar experience with a BMW. Makes me wonder why we don't see a lot more reports of excessive oil consumption with this issue.

and yes, in theory it makes complete sense. Where I raise my brow is when I see intakes with issues and exhausts without or very low mile engines like the ZR1 with excessive guide wear issues. No way those guides had accelerated wear from cooked oil in such a short amount of time.

Who knows.. could be a combo of the two... its just all over the place to point a finger at one reason.

stefuel

What is the exact chemical composition of the coating of the valves in question?

ticat928

The Ti intake has a "chromium-nitride plasma vapor deposition" coating.

http://www.delwestengineering.com/De...niumValves.pdf

The exhaust has no coating:

"The exhaust valves have 2143 stainless steel heads for heat resistance and hollow, sodium-filled, SilChrome stems which are induction-hardened to have a good wear surface for the rocker arms"

http://www.corvetteactioncenter.com/...-engine14.html

erick_e

Only the intake valves are coated for compatibility with the PM guides.

The intakes have a Chrome Nitride (CrN) coating.

Javvy

What is the alloy composition of the Ferrea hollow valves?

Is it different to an OEM composition which looks complicated.

Has a heat transfer test been done on OEM against Solid SS and against the Ferreas?

Dont see how Hib can say they are worse without anything to prove the heat supposition.

I think it is down to poor initial machining, then when they start to wear everything else starts to accelerate it all.

ticat928

Thermal conductivity is proportional to the cross sectional area of the part in question, since the wall thickness of a hollow stem valve is 0.8 mm there is much less material to conduct heat in the Ferrea valve, we may not know it's composition but it is Stainless steel alloy based which would not vary from the OEM valve heat transfer ability per sq.in. of stem cross section



The info below is from Mark2009's post #2778 in this forum, go there to view the temperature distribution diagrams:

"In the chart below, the valve on the left is solid titanium and the valve on the right is hollow sodium filled. I presume this is a 'typical' cylinder head. Testing was done by Manley.
Click the image to open in full size.

http://www.hotrod.com/how-to/engine/...exhaust-valve/

Clearly the majority of the heat transfer from the valve is via the seat, even with the sodium valve. Now the siamese condition of the LS7 seats may alter this ratio somewhat, but I doubt it would approach the level of reversing the majority heat sink in the case of a solid valve.

The following depicts typical stem temperatures in the typical cylinder head; same two valves as the previous chart (altho this time they have the sodium valve on the left):
Click the image to open in full size.
Clearly the sodium valve conducts more heat up the stem than the Ti valve. As to how the sodium valve compares to a solid steel valve, the latter would have to be subjected to similar testing to come up with some viable numbers."
.

Javvy

ticat, the link doesn't work for me

ticat928

fixed it. I have to remember when copy and pasting posts to check the links still work

'06 Quicksilver Z06

The lack of auto manufacturers using a hollow stemmed air filled valve in their engines, (if anyone can name one, well then please do) against the numerous manufacturers using In their engines, solid stemmed stainless exhaust valves, and hollow stemmed sodium valves says a lot.

If air filled hollow stemmed valves are a great idea, then I wonder why manufacturers haven't been using them, and why no auto manufacturer has previously commissioned Ferrea or anyone else to make these hollow stemmed air filled valves for any of their engine offerings.

If "weight" is the be all and end all, then it seems to me that some manufacturer would have long ago, as in "decades ago", since come up with the idea to simply bore out the inside of a solid exhaust valve, cap it off, leave the air inside of it, this saving the "weight" and go for it.

Javvy

I did find this after a quick google, a good read.

http://www.aera.org/engine-professio...ve-technology/

No4Play

Thanks! A lot of it has to do with physically setting the heads up properly. They've pretty much got to be spot on with getting everything aligned and in harmony. It's obviously a tedious job that requires needle point accuracy. When it comes to these heads you have to darn near have a magician as a machinist! These ain't your average 350 sbc heads that can just be slapped together and called good. I also think milling these heads can be detrimental to them as well.

Sent from my iPad using IB AutoGroup

ramairws6

Really? Weird.....that's now I understood you to say it

propain

Try again with a legible sentence....

Its no wonder you didn't understand it...

crazed_z06

I know Im kind of late to the game here, but has anyone had any official correspondence with GM on this issues? I mean, Im sure this forum has all kinds of successful smart people. Has no one gotten together and demanded an official response from GM Corporate?

I went to talk to the dealer and of course they were like, "There's nothing wrong bla bla bla" .. One of the arguments he made was if there was something wrong, GM would issue a recall because they're doing fixes for everything right now to avoid another black eye like they had for the ignition switches.

No one seems to have died from a LS7 failure yet, but a spontaneous engine failure seems like an EXTREMELY DANGEROUS defect. What if an engine were to fail while someone was going 70mph on the highway or something?

Even if GM is a cheap company that doesnt care, it seems like they should be caring a little more right now.