[Z06] Can someone explain these valve problems
10-28-2012, 09:17 PM
#1
Instructor
Thread Starter
Can someone explain these valve problems
I have a street Z06 that have/will not be tracked, it has 26K on it and I have the ability to have the heads checked. I am a little confused on what the general thoughts are when the valve/heads fails. Is it a cause and effect; does the valve guides wear which in turn caused the valve to break? I read where people have the valve guides replaced with bronze guides and replace the exhaust valves with SS exhaust valves why use the valves that come with the vehicle. Is there a problem with the stock valves if there is no guide wear? I do not want to beat a dead horse but it get a little confusing when reading all these post. Thanks
10-28-2012, 09:26 PM
#2
It's a lot to dig through when reading the various posts you'll find on this forum that discusses the issue.
In a nutshell from my understanding is:
1. There has yet to be a determined 100% guaranteed root cause of the failures.
2. It seems to be narrowed down to either defective guides, or potentially weak valves (being that they are a sodium filled, 2-piece) although many other applications use them.
3. There has been some debate on whether one issue causes the other, and then toss in the notion that maybe the head castings themselves are flawed some way and now it's a party.
So, what you are seeing is a combination of potential fixes. Some people are swapping valves AND guides. Others are using stock valves and bronze guides. There's at least one person using SS valves and new OEM guides, and some others are swapping to SS valves, bronze guides as well as aftermarket heads.
I suppose only time will tell which method, if any, holds up. As far as I know there hasn't been anyone report a dropped valve after using one of the above mentioned changes, I believe.
In a nutshell from my understanding is:
1. There has yet to be a determined 100% guaranteed root cause of the failures.
2. It seems to be narrowed down to either defective guides, or potentially weak valves (being that they are a sodium filled, 2-piece) although many other applications use them.
3. There has been some debate on whether one issue causes the other, and then toss in the notion that maybe the head castings themselves are flawed some way and now it's a party.
So, what you are seeing is a combination of potential fixes. Some people are swapping valves AND guides. Others are using stock valves and bronze guides. There's at least one person using SS valves and new OEM guides, and some others are swapping to SS valves, bronze guides as well as aftermarket heads.
I suppose only time will tell which method, if any, holds up. As far as I know there hasn't been anyone report a dropped valve after using one of the above mentioned changes, I believe.
10-28-2012, 09:31 PM
#3
Instructor
Thread Starter
Is it only exhaust valves not intake valves failing are they both filled?
It's a lot to dig through when reading the various posts you'll find on this forum that discusses the issue.
In a nutshell from my understanding is:
1. There has yet to be a determined 100% guaranteed root cause of the failures.
2. It seems to be narrowed down to either defective guides, or potentially weak valves (being that they are a sodium filled, 2-piece) although many other applications use them.
3. There has been some debate on whether one issue causes the other, and then toss in the notion that maybe the head castings themselves are flawed some way and now it's a party.
So, what you are seeing is a combination of potential fixes. Some people are swapping valves AND guides. Others are using stock valves and bronze guides. There's at least one person using SS valves and new OEM guides, and some others are swapping to SS valves, bronze guides as well as aftermarket heads.
I suppose only time will tell which method, if any, holds up. As far as I know there hasn't been anyone report a dropped valve after using one of the above mentioned changes, I believe.
In a nutshell from my understanding is:
1. There has yet to be a determined 100% guaranteed root cause of the failures.
2. It seems to be narrowed down to either defective guides, or potentially weak valves (being that they are a sodium filled, 2-piece) although many other applications use them.
3. There has been some debate on whether one issue causes the other, and then toss in the notion that maybe the head castings themselves are flawed some way and now it's a party.
So, what you are seeing is a combination of potential fixes. Some people are swapping valves AND guides. Others are using stock valves and bronze guides. There's at least one person using SS valves and new OEM guides, and some others are swapping to SS valves, bronze guides as well as aftermarket heads.
I suppose only time will tell which method, if any, holds up. As far as I know there hasn't been anyone report a dropped valve after using one of the above mentioned changes, I believe.
10-28-2012, 09:36 PM
#4
From what I've read its just the exhaust valve's that have broken. However, I think someone posted a exhaust valve breaking so bad it either broken the intake valve too or ended up in the intake altogether.
10-28-2012, 09:43 PM
#5
Safety Car
There has been documentation of guide wear on BOTH intake and exhaust - but the exhaust side has typically been much more severe. Combined with the hollow stem and internal machining concerns of the valve itself, many consider both the guides and valves as weak areas. Solid valves (specifically stainless) tend to withstand abuse to a much longer degree, so you could get more mileage with a solid valve even if the underlying problem persists. Time will tell if this becomes an issue for those making the switch now as a "fix."
However, most of us also assume that worn guides are the most likely precipitating factor in contributing to valve breakage (not always, but most of the time out-of-spec guides accompany any broken valve).
At this point, I think there's a strong case to be made for valve guides coming from the supplier out-of-spec, inducing accelerated fatigue of the valve itself (notably in heavily tracked cars), and highlighting the weakness of the hollow SS valve's design which ultimately results in the valve head shearing off and doing very bad things to your engine.
There is also the consideration of the exhaust valve being non-concentric with the seat, or even machining errors on the rocker arm mounting boss in the heads inducing extreme side-loading; but these two considerations are hard to inspect/measure and insofar appear to be very uncommon.
Unfortunately, there are many theories based on many assumptions - but overall that is the "conventional wisdom" of the forum at this point in time is that the valve guides are either wearing exceptionally fast or just coming from the supplier way out of spec, because this would not have been checked by the GM engine builders during assembly.
10-28-2012, 09:48 PM
#6
Instructor
Thread Starter
Thanks for the help and clearing up this issue
Intake valves are solid titanium, exhaust valves are hollow stainless steel with sodium filler (helps in heat dissipation).
There has been documentation of guide wear on BOTH intake and exhaust - but the exhaust side has typically been much more severe. Combined with the hollow stem and internal machining concerns of the valve itself, many consider both the guides and valves as weak areas. Solid valves (specifically stainless) tend to withstand abuse to a much longer degree, so you could get more mileage with a solid valve even if the underlying problem persists. Time will tell if this becomes an issue for those making the switch now as a "fix."
However, most of us also assume that worn guides are the most likely precipitating factor in contributing to valve breakage (not always, but most of the time out-of-spec guides accompany any broken valve).
At this point, I think there's a strong case to be made for valve guides coming from the supplier out-of-spec, inducing accelerated fatigue of the valve itself (notably in heavily tracked cars), and highlighting the weakness of the hollow SS valve's design which ultimately results in the valve head shearing off and doing very bad things to your engine.
There is also the consideration of the exhaust valve being non-concentric with the seat, or even machining errors on the rocker arm mounting boss in the heads inducing extreme side-loading; but these two considerations are hard to inspect/measure and insofar appear to be very uncommon.
Unfortunately, there are many theories based on many assumptions - but overall that is the "conventional wisdom" of the forum at this point in time is that the valve guides are either wearing exceptionally fast or just coming from the supplier way out of spec, because this would not have been checked by the GM engine builders during assembly.
There has been documentation of guide wear on BOTH intake and exhaust - but the exhaust side has typically been much more severe. Combined with the hollow stem and internal machining concerns of the valve itself, many consider both the guides and valves as weak areas. Solid valves (specifically stainless) tend to withstand abuse to a much longer degree, so you could get more mileage with a solid valve even if the underlying problem persists. Time will tell if this becomes an issue for those making the switch now as a "fix."
However, most of us also assume that worn guides are the most likely precipitating factor in contributing to valve breakage (not always, but most of the time out-of-spec guides accompany any broken valve).
At this point, I think there's a strong case to be made for valve guides coming from the supplier out-of-spec, inducing accelerated fatigue of the valve itself (notably in heavily tracked cars), and highlighting the weakness of the hollow SS valve's design which ultimately results in the valve head shearing off and doing very bad things to your engine.
There is also the consideration of the exhaust valve being non-concentric with the seat, or even machining errors on the rocker arm mounting boss in the heads inducing extreme side-loading; but these two considerations are hard to inspect/measure and insofar appear to be very uncommon.
Unfortunately, there are many theories based on many assumptions - but overall that is the "conventional wisdom" of the forum at this point in time is that the valve guides are either wearing exceptionally fast or just coming from the supplier way out of spec, because this would not have been checked by the GM engine builders during assembly.
10-28-2012, 10:38 PM
#7
Race Director
If you check and your guides are well with in spec at 26K miles, you should be OK. If your exhaust guides are out of spec, you need to replace the guides and the valves as the valves may have suffered some fatigue damage due to the out of spec valve guides. Most here would recommend bronze guides and SS valves. Make sure to check the intake guides also, as these have had a few problems. The issues have occurred as early as 400 miles and at least as late as 85K miles.
Some would recommend bronze guides and stock sodium filled exhaust valves and at least one top vendor replaces with stock guides and stock valves, but makes sure they are in spec when installed.
As mentioned, GM is not really saying what the problem is, probably trying to minimize their obligations and cost to current LS7 customers.
I agree with the prior posts made, too.
Some would recommend bronze guides and stock sodium filled exhaust valves and at least one top vendor replaces with stock guides and stock valves, but makes sure they are in spec when installed.
As mentioned, GM is not really saying what the problem is, probably trying to minimize their obligations and cost to current LS7 customers.
I agree with the prior posts made, too.
10-28-2012, 10:44 PM
#8
Drifting
Intake valves are solid titanium, exhaust valves are hollow stainless steel with sodium filler (helps in heat dissipation).
There has been documentation of guide wear on BOTH intake and exhaust - but the exhaust side has typically been much more severe. Combined with the hollow stem and internal machining concerns of the valve itself, many consider both the guides and valves as weak areas. Solid valves (specifically stainless) tend to withstand abuse to a much longer degree, so you could get more mileage with a solid valve even if the underlying problem persists. Time will tell if this becomes an issue for those making the switch now as a "fix."
However, most of us also assume that worn guides are the most likely precipitating factor in contributing to valve breakage (not always, but most of the time out-of-spec guides accompany any broken valve).
At this point, I think there's a strong case to be made for valve guides coming from the supplier out-of-spec, inducing accelerated fatigue of the valve itself (notably in heavily tracked cars), and highlighting the weakness of the hollow SS valve's design which ultimately results in the valve head shearing off and doing very bad things to your engine.
There is also the consideration of the exhaust valve being non-concentric with the seat, or even machining errors on the rocker arm mounting boss in the heads inducing extreme side-loading; but these two considerations are hard to inspect/measure and insofar appear to be very uncommon.
Unfortunately, there are many theories based on many assumptions - but overall that is the "conventional wisdom" of the forum at this point in time is that the valve guides are either wearing exceptionally fast or just coming from the supplier way out of spec, because this would not have been checked by the GM engine builders during assembly.
There has been documentation of guide wear on BOTH intake and exhaust - but the exhaust side has typically been much more severe. Combined with the hollow stem and internal machining concerns of the valve itself, many consider both the guides and valves as weak areas. Solid valves (specifically stainless) tend to withstand abuse to a much longer degree, so you could get more mileage with a solid valve even if the underlying problem persists. Time will tell if this becomes an issue for those making the switch now as a "fix."
However, most of us also assume that worn guides are the most likely precipitating factor in contributing to valve breakage (not always, but most of the time out-of-spec guides accompany any broken valve).
At this point, I think there's a strong case to be made for valve guides coming from the supplier out-of-spec, inducing accelerated fatigue of the valve itself (notably in heavily tracked cars), and highlighting the weakness of the hollow SS valve's design which ultimately results in the valve head shearing off and doing very bad things to your engine.
There is also the consideration of the exhaust valve being non-concentric with the seat, or even machining errors on the rocker arm mounting boss in the heads inducing extreme side-loading; but these two considerations are hard to inspect/measure and insofar appear to be very uncommon.
Unfortunately, there are many theories based on many assumptions - but overall that is the "conventional wisdom" of the forum at this point in time is that the valve guides are either wearing exceptionally fast or just coming from the supplier way out of spec, because this would not have been checked by the GM engine builders during assembly.
