nate1121

Hi all. Been a while since I've been around the forums. Used to be a regular over on the C5Z side of the house. I'm currently deployed and wont be back state side until October or November but a new car is in my future. Definitely considering a C6Z for all the obvious reasons but the ugly truth about valve failure is a major sticking point. Basically what I'm looking for is just the basic info on addressing this. There are so many posts out there, it's rather difficult just trying to find the bottom line. If I picked up a low mile Z (probably an 08+) I would want to get the valves redone immediately. what's the basic formula? I see a ton about head work and I'm just trying to figure out what exactly is done to correct the engine failure issue and what is extra (stuff people are doing like heads and cams simply because it's a convenient time to do these things). Hope this makes sense. I lost my LS6 to a dropped valve and there's absolutely no way I could buy and enjoy an LS7 without addressing this issue first.

Thanks for the info and patience. I'm sure you guys get sick and tired of answering valve questions.

Mark2009

Only two things really need to be done:

1. Replace the valve guides. American Heritage probably has the best or least risky (deviation from original design) approach on this -- a supposedly better version of the OEM guide.

2, Replace all the exhaust valves (in case any have suffered damage due to running in incorrectly machined heads). Use OEM parts.

Original springs can be reused if pressures measure within spec. Hell, you can probably re-use the valve seals, but make sure the shop measures all the install heights.

Stop using M1 5W30 oil. Go to M1 0W40 if you shop at Walmart, or some boutique oil if you want to splurge (Redline).

grcor

The best description of the issue and the how to fix it that I have found is here: http://www.corvetteactioncenter.com/...-engine18.html

nate1121

Thanks! this is exactly the kind of concise info I've been looking for. I've read a lot of great feedback about American Heritage and their kits. Good to know somebody has gotten it right since GM doesn't seem to be capable of doing so.

Unreal

Agreed with Mark, but the only thing I would change or advise is go with springs/valves/etc that fit your intended use. If it is just a repair and you aren't looking to upgrade, big cam, blower, etc later, then he nailed it. If you are looking at other modifications, there maybe different parts you want to use.

Also intake valves may need to be replaced if there is wear on them. Any of the top quality head shops will look/measure them and advise what needs to be replaced. Stuff like cams, porting, milling, etc is all extra and not needed but as you said, maybe a good time to do that if you plan on doing it at all since it would cut down on labor.

Mr. Gizmo

Some are replacing the guides and using solid one-piece stainless steel valves. The thought is the 2 piece sodium filled valves are fragile and come apart and this problem with the 2 piece valve is made worse by the geometry /angle of the vavles as they are placed in the head causing excessive heat and wear. Its debatable whether this geometry issue is a manufacture flaw or an actual master design flaw of the LS7 head. There is no guarantee that new Chevy LS7 heads or replacing guides and valves is a permenant fix.

My solution is extended warranty good until 2017 on my low mileage 2009 -- then will go with aftermarket brodix heads(5 or 6k cost) if my final decision is to keep this Z as the last super performance sports car I own --- Or I will sell the Z and by a GenV Viper between now and 2017.

AZDANZ06

A couple weeks ago I had another forum member PM me asking about heads, they had it narrowed down to three vendors, "this is not intended for arguing back and forth like other threads", this is how I see things and how I answered his questions:

Alright, I freed up some time to reply.

Katech uses and recommends their own titanium molybdenum coated intake & exhaust valves, with this coating it is only recommended for use with bronze guides, these valves are $ 159.00 each as shown on their website, so that get's very expensive quickly, they use WCCH for machining work, but the heads are assembled at Katech. As long as the machining work is done properly this is a solid set up with the psi springs, titanium retainers, and arp head bolts. They do not recommend the heavy stainless steel valves that WCCH uses and has gone on record with that.

There was Spintron testing done both at Katech and then another test done behind the scenes paid for by members here, a lot of different combinations of valves, springs, and cams were tested. The Heavy Stainless Steel Valves did not fare well with valve bounce, so let's keep this in mind for the next section.

WCCH as you know does bronze guides, reuses the stock intake valves, and then the heavy stainless steel exhaust valves, this did not test well and Katech does not recommend it based upon testing done. Now to be fair WCCH will put any parts you want or send in with the heads, meaning other valves, springs, etc. But their standard fix is what they have listed on their website using stock intake, stainless steel exhaust, and bronze guides.

AHP, they also do all their own machining to their heads in house, uses high quality Newen Contour BB and/or a Serdi 4.0 machines for guides and seats, their PM Guides are made specifically for them by a Valve Guide Manufacturer, they also have Moldstar 90 Guides which are used by top racing teams and also only available through AHP. Both are great guides, keep in mind the factory put in PM guides, not Bronze. Keep in mind Richard from WCCH went on record in a LS Forum stating he prefers PM Guides, but cannot source them or buy them from GM, so he uses Bronze. The Moldstar 90's are expensive and are really recommended if you are racing/tracking you car hard.

AHP spent money and had hardness testing done on the stock guides, bronze guides, their PM & Moldstar Guides - their guides had higher hardness readings than stock or bronze, which in my opinion is important for long term wear. They send out the stock intake valves to Del West for re-treatment and then use the hollow stem Ferrea exhaust valves, these valves are slightly heavier than stock, way lighter than the solid stainless steel valves. The second round of Spintron testing included these valves, they tested great with the psi 1511 springs and titanium retainers. The importance of this combination was the psi 1511 springs with the titanium retainers brought the overall weight down close to stock weight of the exhaust side of the valve train. I would not have any issue using new part # oem valves either as the wall thickness issue was supposed to be corrected, and they cost about the same as Ferrea's. I went the Ferrea route as they are thicker walled than OEM.

You are on point with using the PSI Springs & Titanium Retainers and the ARP Bolts, I would also recommend new GMPP Head & Exhaust Gaskets.

So the safest combinations would be Katech or AH, unless you requested different exhaust valves with WCCH. The downside in my opinion is Katech & WCCH only offer and use Bronze Valve Guides, the Bronze Guides have a hardness reading of 90 HRB, where the AH PM Guides have a hardness reading of 111.1 HRB, the Moldstar 90's have a hardness reading of 104, but they get harder with usage. Compare this to factory stock PM Guides being 74.8 HRB - so interpret this how you want.

It boils down to your budget, and who do you trust doing the machining work on the heads, what guides you think are best for you, and the valve selection. You have the right springs/retainers already chosen. Being in a boosted application you might consider porting the heads, the valve train itself I would keep it light and would personally avoid the heavy stainless steel valves if I were to throw a blower on my Z.

Hope this helps and does not confuse you any further, it boils down to what you choose and who you choose to do the work.

Here is the hardness chart I referenced the number above from.

Unreal

Once again, it depends on application. SS valves, dual springs, Inconel valves, triple springs, beehive, Hollow Valves, Sodium valves all have different pros/cons and trade offs. If it is a stock like application then Stock, PSI beehive, and stock or hollow SS valves are good choices. Once you throw in a cam, and boost, things change. Most are probably going to recommend the ferrara super alloy or an Inconel valve for a high boost high HP application, along with a spring to handle that.

If you are building a 800+rwhp turbo LS7, or 1000+rwhp supercharged car your choices are going to be different. Even a 650n/a huge cam high compression car.

Copy and pasted from Katechs Website for their forced induction package:
"Cylinder heads: LS7 with ARP studs, LSX-LS7 optional for extreme duty applications
•Valves: LS7 titanium intake, inconel exhaust"

jimbob8915

How well do Inconel exhaust valves wear? I bought into the solid SS valves 3 years ago with bronze guides. I worry about revving past 6500.

MTIRC6Z

A "master design flaw"...you're kidding right?

IF it were a design flaw there wouldn't be some LS7s running 200,000 miles and more without a failure. I could go on and on about how wrong the idea is of there being a "design flaw" but just don't have the energy.

It IS a QC issue which once rectified properly will mean there is nothing to fear in the future.

Cheers, Paul.

AZDANZ06

I agree it all depends upon your application, I would say most people are looking to simply fix their heads while others may have more aggressive HP Goals for their car.

MTIRC6Z

While not revving past 6500 does mitigate the issue of your exhaust valves being somewhat heavy it wont help at all IF your guides are worn out.

Also, a solid SS valve will not have any impact on whether your guides have worn excessively.

IF everything was machined properly and to spec 3 years ago you are probably okay BUT it would still be worthwhile having the guides checked in case there was an issue which didn't get addressed when the valves got changed.

Cheers, Paul.

Unreal

Also SS valves don't mean you have bounce or have issues revving past a certain RPM. Plenty of people rev heavy *** solid valves to 8500+ with no issues. It is the complete setup, cam lobes, springs, lifters, pushrods, etc that determine valve train stability. So just saying you have SS valves doesn't mean much without the rest of the equation.

Unless you are boosted and a high HP application, there is no reason to run an inconel valve. They are for high EGT, high temp applications.

As for a design flaw, it could be if the heads meet the print. Everything has tolerances on it, and if they are wearing as designed, that is a design flaw. Doesn't mean all are bad just because it is a design flaw. Now if some are outside of the designed spec, that is a QC issue (or could still be design if the design isn't manufacturable to the spec).

jimbob8915

My heads were rebuilt by RPM. Replaced all guides with new bronze, re-used stock intakes and installed ss exhaust valves with Patriot springs.

juanvaldez

I'm looking at about the same car you are. I want '09 up for the extra oil capacity. I plan on doing the American Heritage with stock exhaust valves. I fell into a set of LS7 heads. Took 'em apart and measured everything. Intakes were all good. Exhaust valve guides were all bad. After reading all the bickering threads and having a look myself, I don't think the exhaust valves are the problem. Any valve will fail at high rpm if it is flopping around in the guide.

AZDANZ06

Time to vote to get an Official Reply from GM on this issue:

https://www.corvetteforum.com/forums...ead-issue.html

WHY TRY?

Everything seems on point, but why stop using M1 5W30?

djfury05

Probably because the 5w30 runs on the lighter side of the 30wt scale. I've seen quite a bit of oil analysis of it on BITOG and always really good results. I went with Pennzoil Platinum 5w30 myself.

rio95

It's possible there is a design flaw and the ones that are lasting are the ones out of spec. Who's knows???

Mark2009

It is marginal for the application. Even the GM engineers admit that. Also high temp evaporation issues (the exhaust valve guide is a very high temperature environment... just covering some obvious bases).

Other oils have better high temp performance/stability, but I would not consider/use any of the mainstream 5W30's (Pennzoil, etc) since they are all EPA oils not specifically designed for engine protection.