[Z06] LS7 valve guide news.
05-16-2015, 05:41 AM
#802
Here's what I think the heads that have gone with no wear are the heads that are machined correctly and have no issues whatsoever, I bet u those were early year heads. As more came out there were more issues with material rocker pre load geometry and so on I think there are only few yes few ls7 heads that are perfect out there and those need to be looked at and studied why others failed... Oiling geometry wrong guides used it can go on and on. But what we really know is that 1 the guide needs lubrication which from factory the guides do not get...then its open road from there.
05-16-2015, 08:36 AM
#804
Pro Mechanic
Pro Mechanic
Thread Starter
Thanks, but that reinforces my admittedly silly theory though. Each of the 2012 & 13s had intake guides out of spec. The other 2012 with bad guides was put into an 09 with the air to air cooler. Other thing is, Hibs 2012 should be taken off the list because his wiggle test was a false positive.
In this thread, both sides are right of course, yes the wiggle test yields false positives for out of spec guides, but out-of spec guides are causing dropped exhaust valves.
Have any 2012 or 2013s dropped valves? Were they exhaust or intake?
In this thread, both sides are right of course, yes the wiggle test yields false positives for out of spec guides, but out-of spec guides are causing dropped exhaust valves.
Have any 2012 or 2013s dropped valves? Were they exhaust or intake?
Now, if this list is for both excessive guide wear and excessive seat runout, then leave my heads on the list because they had intake seats which were out of spec.
There is no question in my mind that, even with the inaccuracy of "wiggle testing" with a dial indicator, the trend with my heads–i.e: that while guide wear was still inside the service limit, the most worn guides had the seats with the worst run out–was that by, say, 25,000 miles the guides would also have been out of spec.
05-16-2015, 12:22 PM
#805
Le Mans Master
Thanks, but that reinforces my admittedly silly theory though. Each of the 2012 & 13s had intake guides out of spec. The other 2012 with bad guides was put into an 09 with the air to air cooler. Other thing is, Hibs 2012 should be taken off the list because his wiggle test was a false positive.
In this thread, both sides are right of course, yes the wiggle test yields false positives for out of spec guides, but out-of spec guides are causing dropped exhaust valves.
Have any 2012 or 2013s dropped valves? Were they exhaust or intake?
In this thread, both sides are right of course, yes the wiggle test yields false positives for out of spec guides, but out-of spec guides are causing dropped exhaust valves.
Have any 2012 or 2013s dropped valves? Were they exhaust or intake?
I don't know if we've seen any dropped intake valves as a result of guide wear yet - unlike the exhaust valves, other factors like over-rev and "too much cam not enough spring" come into play.
Last edited by Dan_the_C5_Man; 05-16-2015 at 12:26 PM.
05-16-2015, 02:21 PM
#806
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There is reactive maintenance: something is about to fail, so get it fixed asap. Very expensive type of maintenance.
There emergency maintenance: uh-oh.....it's already broke, do what you can do to salvage what's left and get the machine running again: asap/asap/asap. No sense bitching about costs, cause we are loosing money by the minute while the machine is down.
There is predictive / preventative maintenance. Inspect at predetermined intervals of varying degrees of complexity. Make educated repairs and/or overhaul based on the inspection results. Costly up front costs, but highest overall payback and highest reliability.
There is run-to-failure maintenance: this is when you have redundant machines and it is cost advantageous to just replace failed machines with new machines when they fail, and there is no operational down time.
Sounds like you are recommending the run to failure philosophy, but there is no redundancy. You can't have it both ways. Pick your poison.
There emergency maintenance: uh-oh.....it's already broke, do what you can do to salvage what's left and get the machine running again: asap/asap/asap. No sense bitching about costs, cause we are loosing money by the minute while the machine is down.
There is predictive / preventative maintenance. Inspect at predetermined intervals of varying degrees of complexity. Make educated repairs and/or overhaul based on the inspection results. Costly up front costs, but highest overall payback and highest reliability.
There is run-to-failure maintenance: this is when you have redundant machines and it is cost advantageous to just replace failed machines with new machines when they fail, and there is no operational down time.
Sounds like you are recommending the run to failure philosophy, but there is no redundancy. You can't have it both ways. Pick your poison.
My engine could have failed due to loose guides but GM took the engine after they replaced it and as far as I know nobody checked the guides. I do know it didn't have any of the symptoms of loose guides. No excessive valve noise no oil consumption when driven on the street and lower than normal LS Series Engine oil consumption when on track. It did have lots of track time, over 40 days of high rpm wide open throttle operation averaging about 100 miles per day. The engine hit the rev limiter or came close to it a fair number of times each of those track days. When the engine let go it was at 6800 rpm but it didn't come apart.
So did loose guides cause the problem or did the valve springs weaken from all of the high rpm, high temperature operation and allow the valve to float enough to hit the piston. Valve float has been a problem with OHV engines for a lot of years and valve springs are known to weaken quite often. Given the history of engine failures in all OHV engines used hard on a track what is the more likely scenario? I submit it is valve springs.
Now checking valve springs is a PM measure. All it takes is removing the valve covers and springs and replacing the valve seals once done.
Bill
05-19-2015, 08:34 PM
#807
Just thinking outside the square and wondered if anyone can offer any info.
It seems heat is at least a contributing factor in this guide issue. And there are videos of cars with changed valves, guides plus roller rockers with low miles and still the guides are totally worn out. I am just thinking maybe the cause is more in the design of software than design of components. From a mechanical point of view one would think all the mechanical suspects have been taken care of yet the wear continues unabated.
Does anyone know what air/fuel ratio the engine goes through between idle right up to 7k.
The reason I ask is that these cars are amazingly fuel efficient for their capacity and I was wondering whether at extremely light throttle settings running down the road, maybe the exhaust valves are getting exposed to blowtorch temps beyond the normal range and cooking the guides at the bottom and starting the wear process.
I realise at low throttle settings the flow of gasses is light but if the temps somehow got way too high it may be enough to start the process.
Just trying to get away from the endless chase of the mechanical bits as suspects because frankly so far that has led nowhere.
It seems heat is at least a contributing factor in this guide issue. And there are videos of cars with changed valves, guides plus roller rockers with low miles and still the guides are totally worn out. I am just thinking maybe the cause is more in the design of software than design of components. From a mechanical point of view one would think all the mechanical suspects have been taken care of yet the wear continues unabated.
Does anyone know what air/fuel ratio the engine goes through between idle right up to 7k.
The reason I ask is that these cars are amazingly fuel efficient for their capacity and I was wondering whether at extremely light throttle settings running down the road, maybe the exhaust valves are getting exposed to blowtorch temps beyond the normal range and cooking the guides at the bottom and starting the wear process.
I realise at low throttle settings the flow of gasses is light but if the temps somehow got way too high it may be enough to start the process.
Just trying to get away from the endless chase of the mechanical bits as suspects because frankly so far that has led nowhere.
05-19-2015, 11:02 PM
#808
Melting Slicks
There has been some recent discussion on the heat issue.
When system is in closed loop running E10 it creates a lean condition. This happens when driven normally.
Look above for ChadyellowZ
When system is in closed loop running E10 it creates a lean condition. This happens when driven normally.
Look above for ChadyellowZ
05-20-2015, 09:31 AM
#809
Burning Brakes
Just thinking outside the square and wondered if anyone can offer any info.
It seems heat is at least a contributing factor in this guide issue. And there are videos of cars with changed valves, guides plus roller rockers with low miles and still the guides are totally worn out. I am just thinking maybe the cause is more in the design of software than design of components. From a mechanical point of view one would think all the mechanical suspects have been taken care of yet the wear continues unabated.
Does anyone know what air/fuel ratio the engine goes through between idle right up to 7k.
The reason I ask is that these cars are amazingly fuel efficient for their capacity and I was wondering whether at extremely light throttle settings running down the road, maybe the exhaust valves are getting exposed to blowtorch temps beyond the normal range and cooking the guides at the bottom and starting the wear process.
I realise at low throttle settings the flow of gasses is light but if the temps somehow got way too high it may be enough to start the process.
Just trying to get away from the endless chase of the mechanical bits as suspects because frankly so far that has led nowhere.
It seems heat is at least a contributing factor in this guide issue. And there are videos of cars with changed valves, guides plus roller rockers with low miles and still the guides are totally worn out. I am just thinking maybe the cause is more in the design of software than design of components. From a mechanical point of view one would think all the mechanical suspects have been taken care of yet the wear continues unabated.
Does anyone know what air/fuel ratio the engine goes through between idle right up to 7k.
The reason I ask is that these cars are amazingly fuel efficient for their capacity and I was wondering whether at extremely light throttle settings running down the road, maybe the exhaust valves are getting exposed to blowtorch temps beyond the normal range and cooking the guides at the bottom and starting the wear process.
I realise at low throttle settings the flow of gasses is light but if the temps somehow got way too high it may be enough to start the process.
Just trying to get away from the endless chase of the mechanical bits as suspects because frankly so far that has led nowhere.
This theory does not support why the intakes show wear.
The randomness of occurrence seems to be best supported by a lack of quality machining problem.
05-20-2015, 11:42 AM
#810
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Yes, a lean mixture might run hotter than a richer mixture but the total heat the valve is exposed to is much greater at wide open throttle where a lot more power is being produced. At light throttle at highway speeds the engine is making about the same amount of power as a high hp lawn tractor.
Bill
Bill
05-20-2015, 12:27 PM
#811
Actually I am recommending run until you have a symptom of loose guides such as excessive valve noise or oil consumption. Checking valve guides requires removing the heads along with the associated problems just removing and reinstalling can cause. It isn't a typical preventative maintenance type of thing.
My engine could have failed due to loose guides but GM took the engine after they replaced it and as far as I know nobody checked the guides. I do know it didn't have any of the symptoms of loose guides. No excessive valve noise no oil consumption when driven on the street and lower than normal LS Series Engine oil consumption when on track. It did have lots of track time, over 40 days of high rpm wide open throttle operation averaging about 100 miles per day. The engine hit the rev limiter or came close to it a fair number of times each of those track days. When the engine let go it was at 6800 rpm but it didn't come apart.
So did loose guides cause the problem or did the valve springs weaken from all of the high rpm, high temperature operation and allow the valve to float enough to hit the piston. Valve float has been a problem with OHV engines for a lot of years and valve springs are known to weaken quite often. Given the history of engine failures in all OHV engines used hard on a track what is the more likely scenario? I submit it is valve springs.
Now checking valve springs is a PM measure. All it takes is removing the valve covers and springs and replacing the valve seals once done.
Bill
My engine could have failed due to loose guides but GM took the engine after they replaced it and as far as I know nobody checked the guides. I do know it didn't have any of the symptoms of loose guides. No excessive valve noise no oil consumption when driven on the street and lower than normal LS Series Engine oil consumption when on track. It did have lots of track time, over 40 days of high rpm wide open throttle operation averaging about 100 miles per day. The engine hit the rev limiter or came close to it a fair number of times each of those track days. When the engine let go it was at 6800 rpm but it didn't come apart.
So did loose guides cause the problem or did the valve springs weaken from all of the high rpm, high temperature operation and allow the valve to float enough to hit the piston. Valve float has been a problem with OHV engines for a lot of years and valve springs are known to weaken quite often. Given the history of engine failures in all OHV engines used hard on a track what is the more likely scenario? I submit it is valve springs.
Now checking valve springs is a PM measure. All it takes is removing the valve covers and springs and replacing the valve seals once done.
Bill
WIGGLE TEST
Does not require cylinder head removal. And I really don't give a rat's *** what "GM" thinks about this, or - YOU.
Your “engine” advise is not good advice. It's irresponsible at best. Stick to advising others how to drive the car, not how to maintain the engine. You are clueless and I’ve lost every shred of patience trying to tell you anything. It’s abundantly clear that you have made up your mind, and you will not listen to anyone, no matter what their background and expertise is.
05-20-2015, 12:59 PM
#812
Race Director
Just take the heads off and have them "fixed" who would want to keep taking the motor
apart every so many miles and do all the bull. I am in the middle of doing mine right now it has 36000 miles figured I was pushing my luck turns out they seemed fine but I did find a lifter that was broke and missing pieces of steel. God only knows where the pieces are. Why wait until your spinning out or putting out a fire from your own oil.
apart every so many miles and do all the bull. I am in the middle of doing mine right now it has 36000 miles figured I was pushing my luck turns out they seemed fine but I did find a lifter that was broke and missing pieces of steel. God only knows where the pieces are. Why wait until your spinning out or putting out a fire from your own oil.
05-20-2015, 02:06 PM
#813
Pro
As for leaving the guides until you hear/see something wrong...Reckless advice. Most of the time, you'll never see or hear anything.
05-20-2015, 02:31 PM
#814
Safety Car
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Completely agree - everything underhood on my car sounded just fine. Every one of my exhaust valves is out of spec including 2 N/R - which translates to "No Reading off scale so bad we were unable to get a reading"
05-20-2015, 06:28 PM
#815
Yes, a lean mixture might run hotter than a richer mixture but the total heat the valve is exposed to is much greater at wide open throttle where a lot more power is being produced. At light throttle at highway speeds the engine is making about the same amount of power as a high hp lawn tractor.
Bill
Bill
05-20-2015, 08:02 PM
#816
Burning Brakes
While you're intitled to your opioin, I disagree 100% My own car didn't have any sounds or use oil ect when it blew 5 years ago, and my last set of heads were out of spec and i never had to pull the heads to find out I did a wiggle test and had to pull them after seeing movement in the guide. This issue is dangerous and with all the worn guides and you seeing all the blown engines you have I really don't see how you could say this. this is what I did today.
Awesome picture chad.
I'm in the same boat as you guys. I spent some time talking with Richard (WCCH) today about my LS9 heads. I'm going to have them addressed at some point too. I only have 4500 miles currently so it's not urgent. But the intake guide wear is generally worse in the LS9 heads then the LS7 head.
Last edited by ClarksZ06; 05-20-2015 at 08:08 PM.
05-20-2015, 11:44 PM
#817
Le Mans Master
GM has about as much integrity on this issue as Hillionaire does on telling the truth.
Since this little screwing I have gotten from GM I have purchase two vehicles and none was a GM product. I guess, I'll get screwed by someone else, but GM will not have the pleasure again.
Since this little screwing I have gotten from GM I have purchase two vehicles and none was a GM product. I guess, I'll get screwed by someone else, but GM will not have the pleasure again.
05-21-2015, 07:18 AM
#818
Burning Brakes
GM has about as much integrity on this issue as Hillionaire does on telling the truth.
Since this little screwing I have gotten from GM I have purchase two vehicles and none was a GM product. I guess, I'll get screwed by someone else, but GM will not have the pleasure again.
Since this little screwing I have gotten from GM I have purchase two vehicles and none was a GM product. I guess, I'll get screwed by someone else, but GM will not have the pleasure again.
The only Chevy I would ever consider is the corvette and now I bought the ZR1 two months ago I'll probably Make this car a keeper and never go back to a GM product.
05-21-2015, 07:34 AM
#819
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While you're intitled to your opioin, I disagree 100% My own car didn't have any sounds or use oil ect when it blew 5 years ago, and my last set of heads were out of spec and i never had to pull the heads to find out I did a wiggle test and had to pull them after seeing movement in the guide. This issue is dangerous and with all the worn guides and you seeing all the blown engines you have I really don't see how you could say this. this is what I did today.
My engine didn't make any noises or use oil either. I am pretty sure it may have had guides that may have exceeded .0037 but I think it didn't blow because of the guides. I suspect it was due to weakened valve springs. That is a more likely scenario than a slightly out of spec valve guide or even a grossly out of spec valve guide.
Weakened springs reduce the rpm limit at which the valves start to float so on engines that are run to red line over and over for several years there is a point when a valve head hits a piston top breaking off and causing a bunch of damage. Yes, the guide may have been loose but the more likely cause was the valve springs needed to be checked. Weakened springs can cause this failure even when the guides are dead nuts perfect.
Bill
05-21-2015, 08:28 AM
#820
Cruising is the passion!
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St. Jude Donor '07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-'19-'20-'21-'22-'23-'24
Just take the heads off and have them "fixed" who would want to keep taking the motor
apart every so many miles and do all the bull. I am in the middle of doing mine right now it has 36000 miles figured I was pushing my luck turns out they seemed fine but I did find a lifter that was broke and missing pieces of steel. God only knows where the pieces are. Why wait until your spinning out or putting out a fire from your own oil.
apart every so many miles and do all the bull. I am in the middle of doing mine right now it has 36000 miles figured I was pushing my luck turns out they seemed fine but I did find a lifter that was broke and missing pieces of steel. God only knows where the pieces are. Why wait until your spinning out or putting out a fire from your own oil.