mistermog

Ok, doing a little research on springs or valves. I have a stock 06 and not sure exactly what happens.

Do the springs break which drops the valve, or do the valves just break and the spring is fine... or both?

I know springs are a not too horrible upgrade to do, just check for 100/300 force on the spring, or better?

For valves, does the weight of the stainless valves matter with a stock setup? I know Katech sticks with the stock valves, but I don't know and all the searching got me confused.

MTPZ06

Theory I have heard is possibly warped valve guides that allow the valve to move off center slightly. When this happens and the valve closes, the valve doesn't seat properly, it bottoms out and snaps off the head from the stem since it's a "two piece" valve. Sounds reasonable...except, what's the reason for warped valve guides?

2k Cobra

Springs can break. Valves can break.

One of these can cause a problem with the other.

MTPZ06

Agreed, but I believe the OP was speaking about the LS7 "Dropped Exhaust Valve" issue that many have posted about. I may have misinterpreted this?

Jasil

Beyond my scope, but the more you read the more this seems to be the case!!

tim414

I am NO EXPERT....but everything I read it sounds like GUIDES especially when more power is added to LS7. I do NOT think it's valves because Katech uses them. Its the guides which are designed for 500 hp motor. Add more power and wear substantially increases and they get sloppy.....

I'm not gonna worry about it as long as the motor stays stock, but as soon as my warranty is out I'm gonna add a tid bit more and plan to change that as part of the added accessories.

EGash

In my case, the springs were intact, the valve broke off at the head.

Ref this thread: http://forums.corvetteforum.com/c6-z...pictorial.html

"Warped" may not be the proper term, perhaps "loose" might be a better description. And this is just one theory (perhaps the leading theory)

The other leading theories are Machining imperfections in the valve seat, and total valve train harmonics/design flaws that cause excessive strain on the valve when adding after market parts (such as springs/cam packages)

MTPZ06

I wouldn't disagree with that.

All I know is, I would most certainly address this first if I'm modding the motor for significant HP increases. I believe Charlie from RPM has an upgrade that uses stainless valves, dual springs, and some other accompanying items for about $2200 installed. Good piece of mind IMO.

hiznhrz

This is clearly the most practical and logical (with supporting facts) explanation I've seen yet...

383vett

Valve guides don't warp. A valveguide is a bronze-phosphor cylinder pressed into the head and the opening honed to specs. The problem is excessive guide wear. If there is excessive valve guide-valve stem clearance, the valve head doesn't seat squarely on the valve seat. The off center pounding causes the 2 piece valve to separate.

ramairws6

BINGO!!

MTPZ06

So I'm assuming that Katech replaces the valve guides? They use the 2 piece valves. If so, wouldn't it make sense for everyone to do this as a PM item?

hapnermw

Replacement of the guide would only work if the problem is the factory guide material.

Since this accelerated wear issue has only been found in heads with sodium exhaust valves, there is higher probability these valves are the primary factor causing the wear.

At present, it is unknown whether this wear issue is limited to the factory guide material or it occurs with both factory and aftermarket valve guides.

What does seem to resolve the issue is replacement of the guides and the change to non-sodium exhaust valves.

SS exhaust valves add 20-30 grams and require springs with higher nose pressure to retain 7100 rpm operation. Katech published an optron test that demonstrates this:

http://gmhightechperformance.automot...nce/index.html

At present, there doesn't seem to be any published data on spintron/optron validation of LS7 valve trains with SS exhaust valves. The result is that the community is now experimenting with a variety of combinations that may or may not lead to other problems.

So, those like myself, who have switched to SS exhaust valves shouldn't be too surprised if some other problem with our adhoc valve train 'design' crops up.

I'm hoping that the added stability of CHE modified rockers and Morel high speed lifters plus the stronger SS valves will handle the extra stress. And the design of the Katech torquer cam was conservative enough to work with my valve train 'design'.

I'm not too pleased that what appears to be a GM design problem has gotten me into the valve train design business. I thought I had avoided this by installing Katech's validated cam/springs/retainers ...

Unreal

Basically no one knows. The vast majority of people never have an issue. Plenty of people have broken pistons, bearings, etc but you don't see a "sky is falling" mentality with those items.

mistermog

Interesting guys, this is exactly the information I was looking for. I did read a bit about the guides and sodium valves, but don't know enough about this to decide what to do about it first.

I know springs would be a much easier job than the valves and guides, but not sure if that would help at all if it was the valves/guides.

Thanks for the info everyone, and Egash, I've been following your post since you posted it. That is what got me considering this work.

Thanks guys...

AirBusPilot

EGash is the first person that has expressed a desire to find out the root cause of this after his failed. While it is rare, we need to figure this out if possible. The others that have had failures don't seem interested in finding out why, they just buy a new motor and move on.

hapnermw

There is a difference between 'sky is falling' speculation and fact. There is concrete evidence that many if not most LS7s have accelerated exhaust valve guide wear. Those who work on these heads, both stock and modified, see it routinely.

What isn't known is what level of engine failure risk this wear creates.

What is known is that worn valve guides and two piece valves are not a good combination.

While only small numbers of sodium valves are self destructing, how many people are comfortable knowing that their LS7s likely have badly worn exhaust valve guides combined with fragile two piece valves.

I was not and every one of mine turned out to be badly worn.

Rock36

So what happened to the broken spring issue? That has been a definite cause for some of the failures. I don't think that can be discounted.

But at any rate, where can one purchase new valve guides? Will it require complete head removal?

As for the exhaust valve itself, I do know that Katech is confident there is nothing wrong with them. Anyone can call and ask them if you don't want to take my word for it

ramairws6

Wow, why is this the only guy that gets it!? The deal is that after we run a higher lift cam the sodium filled valves are coming out of the guide more and creating more heat. The excessive heat is wearing the guide faster then normal=valve head does not sit down flat on the seat and Whamo!! Breaks the head of the valve off ....

mistermog

But that wouldnt explain the stock engines popping valves, correct?