philpacs

I am having head work completed on a new GM heads from a crate LS7. When asking the well respected machine shop to upgrade the exhaust valves he said they had the "newer valves" and are thicker walled than my early version Z. He said I didn't need to go SS and the stock guides would be fine. He said heat is the culprit as the old couldn't take extended heat. Did GM replace the exhaust valves with better ones? If so should I leave them alone or upgrade the valves? If I should upgrade what do you recommend? I plan on doing a handful of HPDE per year. Thanks for your replies.

tim414

there was a p/n change. however, there has still been wear found since then. if your heads are already at the shop, go ahead and do it. no regrets that way....

'06 Quicksilver Z06

Did something happen to the original motor that was in this car?

http://forums.corvetteforum.com/c6-z...post1580935226


Tell him to show you some proof of the "upgrade" of the stock valves and their ability to resist more heat than before.

There was a part number change in 2008, but nobody has to tell you that since that part number change, valves have dropped in here.

Normally, my advice would be to tell you to go with solid stainless valves.

But since there is no guarantee that this particular shop is going to use the right springs with solid stainless valves, ( I would not have much confidence in them doing so, considering they are telling you about an "upgrade" to the stock hollow stemmed valves, which has been unproven and nobody else seems to know about. Yes, there was a part number change back in 2008. But that is all that there is evidence in an "upgrade" of so far) I wouldn't recommend that.

This is why IMO, it is so important to go with a head shop which has a lot of experience using the most solid fix known out there, and that is the SS valve/bronze guide setup.

But do a little research, and you will find at least 3 2009 cars in here which have dropped exhaust valves.

philpacs

Yes, the valve dropped on my 06Z' w/30K miles while not pushing the motor hard. The valve broke and took out motor. The pictures are heart breaking. I got a crate motor through the extended warranty and decided to do some work while the engine was out.

Thanks for the advise. I am leaning toward the proven fix like you said. The shop also mentioned bronze guides didn't conduct heat as well. He came highly recommended but his advise differs what I've been reading. It's hard to know who to believe.

'06 Quicksilver Z06

You have your answer Phil.

Solid stainless valves unless you want to risk a repeat of what happened to you earlier.

BTW, which warranty company?

Also, for those reading this, it will show that this was a previously u reported broken valve failure, which is not mentioned in Phil's prior posts.

I just throw that out there for those who don't believe that this is as big of a problem as some have said that it is.

This isn't the only unreported failure in here.

Anyway, good luck to you Phil. Do it right with the stainless steel valves, because next time, you might not and probably won't, get a new motor under warranty should it drop a valve.

FrankTank

If I were in your shoes and already lost 1 motor, I would get a second opinion (or heck 3rd or 4th).. it can't hurt. Make a few more phone calls to some very experienced shops and see what they recommend. Most of the vendors here are all recommending the same type of fix as Quick points out. Maybe the guy you spoke to is in fact correct... but that is a lot of faith, and money into taking his "word" for it. Does that shop warranty the work they do? Just curious if he's willing to stand by what he told you.

FNBADAZ06

IMHO, if the OEM guide's improper machining have proven to be the culprit, have new bronze guides put in the new heads by a respected head shop like WCCH, and keep your OEM springs and valves. Simple and cheap fix.

If you do replace the exhaust valves with a SS version, you'll also need to replace the springs and retainers....even if you're staying with the stock cam.

philpacs

Just spoke with Jason from Katech. Maybe he can correct me if I misquote. What I got from him since the engine is new GM has addressed the guide problem in machining and he feels there is no problem with the newer stock valves. He doesn't recommend SS valves because of weight I believe he said. He said if I wanted extra insurance and did bronze guides I would need to change the valves and recommended his ti moly's compared to polished or otherwise(2.5K). Interestingly he said GM has not responded why they changed the valves. Hard to argue with Jason's knowledge but there's still other views/experience making decisions hard. Thoughts?

It was a GMPP warranty but the shop will only warranty problems due to his work not others parts. Ill open a new thread with pics of my valve caused engine damage to document another case.

'06 Quicksilver Z06

Your car is an '06.

According to GM, there was mismachining issue then.

Did he tell you what those Ti/Mo exhaust valves cost?

Since you're dealing with the heads, can you have the shop measure stem to guide clearance in this new engine? A few would like to know what these numbers are in a new set of the latest heads.

Since the next motor which fails, will be on you, choose wisely.

Mark2009

Based on various measurements and some posted data, the newer (post 2/08) valves appear to weigh 3% more than the older (2006) valves (74.0 grams vs 71.7). Dunno exactly what that means, but it does tend to support what your shop said. But it does not necessarily mean the newer valves are any better than the older valves. Conversely, it does not necessarily mean that there was anything wrong with the older valves, or at least anything wrong with them that led them to break.

Manganese bronze, a proprietary mix of which is used by possibly the major performance valve guide manufacturer (CHE) has about double the thermal conductivity of plain iron. Other types of bronze may the the same or worse than iron. I don't know what the value is for the iron alloy/mixture used in the OEM guides.

Some condemn the OEM exhaust valve for breaking without caring why it broke. The failure mode appears to be extremely excessive valve guide wear -- up to quadruple the service limit or even beyond -- allowing the valve to wobble in the guide to the extent that it eventually snaps the stem. So it doesn't appear to be heat making the valve fail, but very well could be heat -- perhaps in combination with something else -- causing the guide to fail (wear out). On the other hand, instead of heat it could be an excessively rough valve stem or a machining error during manufacture. Could be that the heat conducting nature of the OEM valve is overwhelming the OEM guide and destroying it. Could be that the heat conducting nature of the OEM valve is overwhelming the lubricating properties of the OEM engine oil (although the OEM guide is supposed to have some lubricating properties of its own). Could be sunspots. Could be the Matrix (do you really want to take the red pill?)

Despite internet claims of solid stem stainless valve invulnerability, it is quite possible that a solid stem valve would fail just like the OEM hollow stem valve does. Perhaps it would take longer, but the same fatigue mechanism would surely come into play sooner or later. It would seem to me that the smart move would be to address or at least check and monitor the guide wear, rather than installing a part that you think will better withstand abuse that shouldn't be happening in the first place.

So if you can keep the guides from wearing, or at least monitor the guide wear, the OEM setup should be fine. Since we don't know exactly what is causing the guides to wear, and GM ain't talking (except vaguely), you're left with monitoring them. At this point it should be noted that the solid stem / bronze setup should be monitored as well... given the unknowns it would be foolish to not do so (some industry people claim the bronze will wear quickly with the OEM style rocker, so the various industry opinions and claims are contradictory and all over the map). Since your engine is at a shop that I presume is going to install it, and local to you, I would ask them about their familiarity with what has become called the 'wiggle test', which -- ideally using a dial indicator -- allows guide wear to be approximated without removing the heads. If they know what you're talking about, see what it would cost to have this done:
1. now, as a baseline, and
2. after, say, 5K miles as a followup, and
3. every 5K or 10K miles after that, depending on the trend.
They'll probably charge at least a couple hundred bucks; it's a bit of time consuming job, especially to do all 8 cylinders. If the guides don't wear, and if you don't overrev the engine, you should be okay on valve drop regardless of the type of valve in the engine.

If the OEM valves would keep you awake at night, then go ahead and have the new heads removed from the engine and shipped out for rework with the 'fix du jour'. Peace of mind is worth more than theory and conjecture and, in some cases, facts

'06 Quicksilver Z06

Who said anything about "solid stem stainless valve invulnerability"?

Phil a few words of advice for you. First off, they're liable to laugh in your face, if you go in talking about some "wiggle" test. And rightfully so. And then laugh even harder when you start talking about doing it every 5K miles.

Secondly, you said that you intend to do HPDEs with your car, and indeed that you have done HPDE's in it.

The above "advice" in that post, comes from a guy whose car, by his own admission, has never even ever seen redline.

Now Phil, you say that you run HPDEs. Again, I'd advise you to choose wisely.

Some can afford to pontificate, and talk about "could be", and such.

You have already popped a motor due to these valves. You have suffered one engine failure, and dodged a bullet this time in that you had warranty coverage.

You pop another motor at the HPDE's, then it won't be people who have never seen redline, and who pontificate about what "could have been" this or that, who will be paying for it. They didn't pay for it the first time you had a motor pop. They stood on the sidelines. They won't be paying for it the next time it pops.

No, it won't be them paying for it if it pops again. It will be YOU.

Now if I recall, you said:

So like many in here, it sounds like you can ill afford to listen to theories and such from people who are taking no risk, and who's rear ends aren't in the wind if this "blows up in your face again", no pun intended.

They aren't going to be there, when it does. They will putting their two cents into the next thread of the next guy who has a motor pop, telling him how everything is alright with the stock hollow stemmed valves, that he should go right back to a set of heads with them, while at the same time they're telling him this, antifreeze and motor oil are still pouring from the freshly made hole in his engine block, and what's left of his motor, is still warm.

How much did that new motor you just got, cost? How much is it going to cost to install it?

And now, can you afford that, out of pocket, if it should occur again? You don't have to answer "out loud", just ask yourself that question.

Make the best move Phil.

Get yourself a good set of solid stainless valve, bronze guides and the right valve springs and drive the HPDE's to your heart's content, with little to no worry about this matter ever again.

http://forums.corvetteforum.com/c6-z...st-valves.html

Or you can follow the path of Scuba_Steve and VRedZ06, stick with the stock OEM hollow stemmed exhaust valves, and end up like them. Or you can learn from their mishaps.

The choice is yours.

http://forums.corvetteforum.com/c6-z...-hard-dea.html

http://forums.corvetteforum.com/c6-z...post1578507241

He learned his lesson. But he learned it too late.

http://forums.corvetteforum.com/c6-z...post1578507425

As did Scuba_Steve.

Again, learned his lesson, had seen all of the posts talking this and that about "valve train weight" and "slaughtering your redline", "engine won't rev up to 7K RPM" because the "SS valves make the valve train too heavy" and such, he apparently listened to it, and he ended up learning the hard way.

After this incident, Scuba_Steve, had this to say:

http://forums.corvetteforum.com/c6-z...post1573731770

Apparently, he had seen enough to deter him from going the same route as he had prior to his engine failure, and he put solid stainless steel valves in it.

This car failed pretty quickly according to Steve.

Do yourself a favor Phil. Don't you be next. Don't let people talk you into being the next "candidate" for the two time dropped valve club. Let someone else be next.

jedblanks

So it looks like a stock valvetrain holds up for 20k-25k miles of hard driving.

Does anyone have 25k hard miles on a SS valve / bronze guide setup?

MP&RPZ06

Jason told me the same thing in regards to SS valves weight, I am waiting for results of his testing to be done.

Mark2009

Available evidence does not support that claim. Some hold up for 5K, some hold up for 88K. Some are still holding up. Clearly there is some kind of problem with many LS7 heads related to the exhaust valve guides.... trying to narrow it down to a 'danger range' is unwise.

The prudent thing to do is check the guide wear. If you have excessive wear, you have a problem. If you don't have excessive wear, you don't have a problem (but you should continue to periodically check, regardless of your type of valvetrain).

'06 Quicksilver Z06

25K miles on Ferrea super alloys, which are some of the heavier exhaust valves out there in use in these cars.

http://forums.corvetteforum.com/c6-z...post1582764956

14K miles on ChadyellowZ06s car
http://forums.corvetteforum.com/c6-z...post1582767195

JwT

This is excellent advise Op. I would take it ASAP. It's your choice. If you don't, we will hearing from you very soon and the news won't be good.

briancb1

Solid exhaust valves with Bronze guides do work. It's been done for decades. How long does it hold up? Well how do you drive and how aggressive are your lobes? Etc.
lots of variables to consider. Bronze guides will wear out eventually, question is when.

Michael_D

Sodium filled, hollow stem exh valves are considered an "upgrade". They were widely used in NASCAR and other high rpm (8000+) race engines till Ti became the alloy of choice. They've been is use for decades, and will continue to be used. They work excellent for what they were intended to be used for - enhanced thermal flux transfer in applications where there is a LOT of flow, but normal EGT's. The LS7 exh port fit's this description.

It is a human tendency to become fixated on the failure, and to let emotion and prejudices guide their deductive reasoning. I earn a paycheck keeping critical machinery running and improving reliability. I have sat through hundreds of root cause analysis work shops. There is a reason why root cause analysis must be done with rules and structure in place to avoid the aforementioned emotional fixation.

In regards to these heads, GM has gone on record saying something to the effect that the machine work was screwed up on some heads. Not all, but some. When you read through the lines, this means that one of the contractors who got the "post-cast" machine work contract from GM was doing something incorrectly. This was detected. Keep in mind that GM has contracted out this work to more than one contractor, I have heard three, but can't confirm that.

Improper machining can, and will, cause premature valve failure. Doesn't matter what alloy or design, they will fail. Some will take more abuse than others, but eventually, they will fail.

There is a rub that I have an issue with regarding GM's statement, and that is the effected model year. Unless GM knows for certain which heads were machined incorrectly, and what short block they got bolted to, and which car that engine was installed in, then how could they possibly know which car could be plagued with this???? I would be amazed if GM has their shiit sooooo squared away that they actually know this information. That would be like saying they know exactly which headlight that was manufactured on Nov 15th, 2011 and which GMC truck that headlight was installed. I suspect that all the heads are boxed and stored in a warehouse together, all with the same skew number / part number, and there is no way to tell which one was machined where or when. I may be wrong with that assumption. Hopefully I am.

So what I would do, and this goes for anyone who either owns a Z06 or is getting a "new" engine, is to do as Mark suggested above. Check the guides for excessive clearance. If you have a "new" engine that is about to be installed, or a "new" set of GM heads, take them to a reputable shop that works cylinder heads. Not some garage mechanic, but someone who works heads for a living. Have them disassemble the heads and verify guide clearance and seat run out. If those two things are within spec, bolt them back on and run the car like you stole it.

That's just one guy's opinion of course, and you know that old saying about opinions..... especially when they are free.