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C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
Thanks for at least "trying" to get the word out... I guess it's like politics or gun control, people get their minds made up and refuse to listen to the other side. As I get older, I try to understand both sides of the debate. I heard both sides when I bought mine, had them checked and they were out of spec., I had them done, if I have an issue now, I will be part of the study that can say "the fix" didn't fix it.
I'm sure you have read your share here..lol I said in the past that I was 100% sure the problem was the valve and that bronze valves guide was the fix, I was sure of it, all I ever used was bronze valve guides in all high hp cars this was the late 80's it always worked well so I never changed still wont in high hp cars. once I seen my 3rd set with ss valves bronze valve guides come back bad I knew I was wrong and indeed gave false info to the forum. but at the time their was many ppl saying there was know problem at all.Now I do think bronze an ss valves will last longer some may never were how knows, I've seen 2 heads in spec in 5 years out of 78 heads one was forum member z05 505 24k track miles only. all 16 was in spec and I posted the guide sheet. another was a set of wcch heads with 20k miles if I remember right. all 16 guides were in spec, guy from tampa fl friend of mine that beat the hell out of his car each weekend if it didn't rain at the local drag strip. I think there are many factors at play here, we may never find a 100% fix but the ss valve is by far the better choice in these cars with guide wear that we are seeing, a solid stem should be a no brainer. I tried to help the forum I really did after siding in my own oil it really scared me if I would have been over 100 I doubt i'd be here today, just check the damn guides is all i'm saying to do, reguardless of what fix or who has what. this problem i believe and i'll put my name on the line that if left unchecked 90% will be out of spec by 30k if they are not out of spec with that many miles I wouldn't change a damn thing in the heads...hope this helps some of you guys. I wont have the time to post much but i'll be on here an there...take care guys an check your damn guides every 10K
Last edited by chadyellowz; 07-10-2015 at 03:28 AM.
i will man i broke my cell and the wife has been dealing with my fb page. Been busy as hell need to hire another guy.pm me your number again i lost all my contacts an i'll call you from my wifes cell
We have been saying for years that Bronze is the wrong material for the LS7 application (with stock rockers). That's why we use our proprietary Hardened Powder Metal valve guides. For those that want a more "exotic" alloy we offer our Moldstar90 Valve guides (which is superior to bronze in EVERY WAY).
We have reworked many many bronze and solid ss valved heads from aforementioned head rework shop. The bronze guides and solid ss valves is not the "fix" most are looking for.
Why use heavy solid ss valves when there are so many other options available. If the head falls out of spec its out of spec, all a solid ss valve is going to do is take longer to break. If everything on the head is done properly the head should not fall out of spec (anytime soon) and the thickness of the valve will not matter.
In our opinion adding a solid ss valve to the head is not the correct way to go and could even be viewed as a "crutch" of sorts.
Last edited by American Heritage; 07-10-2015 at 06:21 PM.
I took my car up to Abel Chev little over a year ago (Feb. 14, car had 28K miles) for a wiggle test since it was in the bad machining "window" (here's the thread https://www.corvetteforum.com/forums...ggle-test.html). They found a couple loose ones so I got new GM performance heads on warranty. Runs a little quieter now, so I have no worries. I also have a GMPP to cover me after the powertrain warranty expires next March. Your's being a '13, I wouldn't worry about it too much unless it's making a lot of noise.
Thanks, mine's a 2012. I did purchase 4 years of a GMMGP warranty with the $100.00 deductible. Will most likely have the heads gone through sooner than later. Not my DD either.
We have been saying for years that Bronze is the wrong material for the LS7 application (with stock rockers). That's why we use our proprietary Hardened Powder Metal valve guides. For those that want a more "exotic" alloy we offer our Moldstar90 Valve guides (which is superior to bronze in EVERY WAY).
We have reworked many many bronze and solid ss valved heads from aforementioned head rework shop. The bronze guides and solid ss valves is not the "fix" most are looking for.
Why use heavy solid ss valves when there are so many other options available. If the head falls out of spec its out of spec, all a solid ss valve is going to do is take longer to break. If everything on the head is done properly the head should not fall out of spec (anytime soon) and the thickness of the valve will not matter.
In our opinion adding a solid ss valve to the head is not the correct way to go and could even be viewed as a "crutch" of sorts.
Could you be more specific by what you mean by "out of spec" as it relates to the head..Tx
We have been saying for years that Bronze is the wrong material for the LS7 application (with stock rockers). That's why we use our proprietary Hardened Powder Metal valve guides. For those that want a more "exotic" alloy we offer our Moldstar90 Valve guides (which is superior to bronze in EVERY WAY).
We have reworked many many bronze and solid ss valved heads from aforementioned head rework shop. The bronze guides and solid ss valves is not the "fix" most are looking for.
Why use heavy solid ss valves when there are so many other options available. If the head falls out of spec its out of spec, all a solid ss valve is going to do is take longer to break. If everything on the head is done properly the head should not fall out of spec (anytime soon) and the thickness of the valve will not matter.
In our opinion adding a solid ss valve to the head is not the correct way to go and could even be viewed as a "crutch" of sorts.
Could you be more specific by what you mean by "out of spec" as it relates to the head..Tx
My reading of that comment is it applies to the well known GM Service Spec of .0037 valve guide clearance shown in this picture:
Those are the specs used to determine whether or not to redo the guides or replace the heads. As you can see the max production line spec is ~ .0011-.0013 less than the max Service Spec depending on whether you are talking about an exhaust or intake valve.
You don't get valve drops until the clearance gets way above the .0037 number. If you have the heads apart and get measurements above .0037 GM says to fix the issue. If the heads are on the engine and not disassembled you get into another question of whether or not you should do anything if the measurement is .0038. The problem is reading the clearances on a fully assembled head on an engine in the engine compartment (the so called wiggle test). It isn't easy to set up the equipment and ensure the accuracy of the measurements.
There is no definitive data that proves excessive valve guide clearances caused the rash of valve drops that were reported on this forum 4 and 5 years ago. It is only a theory based on recommendations from various shops and a GM acknowledgement that a certain range of production heads had a machining problem.
At the time there were all sorts of theories about why the valves were dropping including aftermarket cams, aftermarket rocker arms with different ratios than stock, the stock exhaust valve design and build, etc. The problem is although 9 out of 10 failures were due to dropped exhaust valve heads there were some intake failures as well so the exhaust valve theory didn't quite fit. The aftermarket parts theory didn't quite fit either since a lot of the engines that failed had stock valve systems. Then we had the guide clearance theory which has some issues as well. First, the percentage of loose intake guides reported is much higher than the percentage of reported failed intake valves (that may be because the intake valve is a solid valve). Second, there are no definitive answers on how loose a guide has to be to actually cause a valve head to break off. My engine builder said he had worked with a lot of LS heads in the $40K+ 9000 rpm race engines that he builds and had never seen or heard of an LS engine issue due to loose guides. He said those kinds of engines don't come with warranties but the people who spend that kind of money for an engine do tend to get upset if one comes apart for something that might be considered a build or design error. His biggest bug a boo was the race team that bought one of those engines and at the end of the racing season let it sit till they hit the track again the next spring and tried to run it at 9K rpm and blew the engine. The usual cause was the valve springs weakening thus not being able to sustain that rpm level any more which led to pistons and valves colliding. The teams that threw on a fresh set of springs usually didn't have any problems. His experience led him to believe even on street engines if you have valve heads breaking off you need to look at the springs first.
I know the head of the exhaust valve on my engine went into the intake manifold. What I don't know is whether it hit the piston due to a weakened valve spring while running at 6800 to 7000 rpm for the umpteenth time, a valve guide had excessive clearance (there was no noise or excessive oil consumption) or the exhaust valve failed due to a poor design/build. The resulting fix coming out of all that is redo the guides (with bronze/PM), install solid SS valves which on the face of things looks like it is a guess that is trying to cover several possible causes of the failure.
As for GM addressing the problem they addressed a fair number of engine failures by replacing the engines under warranty. Out of 9 failures I personally knew about GM replaced 8 of the engines. The 9th had several engine mods including a cam, headers and a tune and the owner never asked them to cover the problem. As far as I am concerned they stepped up to the problem and did the right thing and did it multiple times.
We are here because of engine failures caused by valve drops not because of loose guides. Saying GM is ignoring the loose guide issue is ridiculous since there is no proof that loose guides were the cause of the initial rash of valve drops or the few that are being reported now. Yes, some of the failed engines did have loose guides as we have seen in various videos but we don't know what other things may have been going on at the same time. Some times we do get smoke where there is no fire and we get fire where there is no smoke. There is a lot of smoke around the valve guide clearance at this time and there isn't a lot of material to help you make an educated guess.
I am not bashing any of the other engine builders or machine shops that are offering solutions based on their experience that address what is definitely a Customer Concern issue. However, if loose guides are the real cause of dropped valves why is there a mixture of solutions? Why isn't fixing the guides properly the only solution? Why the insistence on replacing the stock exhaust valve with a solid ss valve? If the guides are the issue the valve shouldn't need to be replaced. That to me means the people recommending that solution are not sure about the cause of dropped valves and trying to cover as many possibilities as they can. If you trace the history of this discussion over the last 4 years you can see that lack of certainty all the way through.
Now here is my truth in lending statement. Early this year I was worried about the guides in my replacement engine (due to all of the hype). I had Peter Gibbons, Motorsports in Mooresville, NC remove the heads and check the valve guide clearances using a valve guide bore gauge to check the bores in 3 locations and a micrometer to measure the valve stem diameters. All valve stem diameters were within the production sped shown in the picture above. All but two intake guide clearances were within the .0037 spec and two were measured at .0039. No exhaust valve guide clearance was out of spec or close to being out of spec. This was after ~13K miles with about 4K of them being high rpm wide open or close to wide open track miles.
GMPP looked at the data and Peter's shop and approved replacing the heads due to the two intake guides being out slightly out of spec. Peter said the new stock heads were fine for the street and doing a few track days but If I thought I would be doing a lot of track days then I should look at increasing the reliability of the valve system. Those comments and suggestions that Jason at Katech made based on my engine usage led me to have the heads modified with bronze guides and Ti/Mo intake and exhaust valves.
I got the car back at the end of April and since then I have put about 500 miles of track usage (7 track days) on the engine with multiple trips to the 6800 to 6900 rpm level with no issues. I will be going back to Peter early next year to have him check the valve springs before I head out for more track days.
As Peter told me when he reported his initial findings, "You can more than likely just reassemble the heads and have no concerns." My problem I was stuck in a situation where GM's service guidance says to replace a head where the clearance is above .0037, the heads were apart and now was the time to do something Vs reassembling or installing the new stock heads. It took me several weeks to make up my mind. It wasn't as easy as when replacing a clutch pressure plate you say while I am in there I am going to replace everything due to the effort required to take everything apart and put it back together again.
I might have been better off not doing a damned thing, never having the heads checked and driving the car since I still have close to three years of GMPP no deductible coverage left.
Before you decide what to do recognize this isn't a clear cut situation. There may not be a problem to solve and if there is there are no clear cut solutions. Remember the old adage, Don't Fix it if it isn't Broken. Do your Due Diligence. Caveat Emptor.
My reading of that comment is it applies to the well known GM Service Spec of .0037 valve guide clearance shown in this picture:
Those are the specs used to determine whether or not to redo the guides or replace the heads. As you can see the max production line spec is ~ .0011-.0013 less than the max Service Spec depending on whether you are talking about an exhaust or intake valve.
You don't get valve drops until the clearance gets way above the .0037 number. If you have the heads apart and get measurements above .0037 GM says to fix the issue. If the heads are on the engine and not disassembled you get into another question of whether or not you should do anything if the measurement is .0038. The problem is reading the clearances on a fully assembled head on an engine in the engine compartment (the so called wiggle test). It isn't easy to set up the equipment and ensure the accuracy of the measurements.
There is no definitive data that proves excessive valve guide clearances caused the rash of valve drops that were reported on this forum 4 and 5 years ago. It is only a theory based on recommendations from various shops and a GM acknowledgement that a certain range of production heads had a machining problem.
At the time there were all sorts of theories about why the valves were dropping including aftermarket cams, aftermarket rocker arms with different ratios than stock, the stock exhaust valve design and build, etc. The problem is although 9 out of 10 failures were due to dropped exhaust valve heads there were some intake failures as well so the exhaust valve theory didn't quite fit. The aftermarket parts theory didn't quite fit either since a lot of the engines that failed had stock valve systems. Then we had the guide clearance theory which has some issues as well. First, the percentage of loose intake guides reported is much higher than the percentage of reported failed intake valves (that may be because the intake valve is a solid valve). Second, there are no definitive answers on how loose a guide has to be to actually cause a valve head to break off. My engine builder said he had worked with a lot of LS heads in the $40K+ 9000 rpm race engines that he builds and had never seen or heard of an LS engine issue due to loose guides. He said those kinds of engines don't come with warranties but the people who spend that kind of money for an engine do tend to get upset if one comes apart for something that might be considered a build or design error. His biggest bug a boo was the race team that bought one of those engines and at the end of the racing season let it sit till they hit the track again the next spring and tried to run it at 9K rpm and blew the engine. The usual cause was the valve springs weakening thus not being able to sustain that rpm level any more which led to pistons and valves colliding. The teams that threw on a fresh set of springs usually didn't have any problems. His experience led him to believe even on street engines if you have valve heads breaking off you need to look at the springs first.
I know the head of the exhaust valve on my engine went into the intake manifold. What I don't know is whether it hit the piston due to a weakened valve spring while running at 6800 to 7000 rpm for the umpteenth time, a valve guide had excessive clearance (there was no noise or excessive oil consumption) or the exhaust valve failed due to a poor design/build. The resulting fix coming out of all that is redo the guides (with bronze/PM), install solid SS valves which on the face of things looks like it is a guess that is trying to cover several possible causes of the failure.
As for GM addressing the problem they addressed a fair number of engine failures by replacing the engines under warranty. Out of 9 failures I personally knew about GM replaced 8 of the engines. The 9th had several engine mods including a cam, headers and a tune and the owner never asked them to cover the problem. As far as I am concerned they stepped up to the problem and did the right thing and did it multiple times.
We are here because of engine failures caused by valve drops not because of loose guides. Saying GM is ignoring the loose guide issue is ridiculous since there is no proof that loose guides were the cause of the initial rash of valve drops or the few that are being reported now. Yes, some of the failed engines did have loose guides as we have seen in various videos but we don't know what other things may have been going on at the same time. Some times we do get smoke where there is no fire and we get fire where there is no smoke. There is a lot of smoke around the valve guide clearance at this time and there isn't a lot of material to help you make an educated guess.
I am not bashing any of the other engine builders or machine shops that are offering solutions based on their experience that address what is definitely a Customer Concern issue. However, if loose guides are the real cause of dropped valves why is there a mixture of solutions? Why isn't fixing the guides properly the only solution? Why the insistence on replacing the stock exhaust valve with a solid ss valve? If the guides are the issue the valve shouldn't need to be replaced. That to me means the people recommending that solution are not sure about the cause of dropped valves and trying to cover as many possibilities as they can. If you trace the history of this discussion over the last 4 years you can see that lack of certainty all the way through.
Now here is my truth in lending statement. Early this year I was worried about the guides in my replacement engine (due to all of the hype). I had Peter Gibbons, Motorsports in Mooresville, NC remove the heads and check the valve guide clearances using a valve guide bore gauge to check the bores in 3 locations and a micrometer to measure the valve stem diameters. All valve stem diameters were within the production sped shown in the picture above. All but two intake guide clearances were within the .0037 spec and two were measured at .0039. No exhaust valve guide clearance was out of spec or close to being out of spec. This was after ~13K miles with about 4K of them being high rpm wide open or close to wide open track miles.
GMPP looked at the data and Peter's shop and approved replacing the heads due to the two intake guides being out slightly out of spec. Peter said the new stock heads were fine for the street and doing a few track days but If I thought I would be doing a lot of track days then I should look at increasing the reliability of the valve system. Those comments and suggestions that Jason at Katech made based on my engine usage led me to have the heads modified with bronze guides and Ti/Mo intake and exhaust valves.
I got the car back at the end of April and since then I have put about 500 miles of track usage (7 track days) on the engine with multiple trips to the 6800 to 6900 rpm level with no issues. I will be going back to Peter early next year to have him check the valve springs before I head out for more track days.
As Peter told me when he reported his initial findings, "You can more than likely just reassemble the heads and have no concerns." My problem I was stuck in a situation where GM's service guidance says to replace a head where the clearance is above .0037, the heads were apart and now was the time to do something Vs reassembling or installing the new stock heads. It took me several weeks to make up my mind. It wasn't as easy as when replacing a clutch pressure plate you say while I am in there I am going to replace everything due to the effort required to take everything apart and put it back together again.
I might have been better off not doing a damned thing, never having the heads checked and driving the car since I still have close to three years of GMPP no deductible coverage left.
Before you decide what to do recognize this isn't a clear cut situation. There may not be a problem to solve and if there is there are no clear cut solutions. Remember the old adage, Don't Fix it if it isn't Broken. Do your Due Diligence. Caveat Emptor.
Bill
Long response Bill but I don't know if this explanation is what AH was referring which is why I asked for an clarification. My initial read of what AH meant about falling out of spec is a reference to the OEM guides not being hard enough in an LS 7 application. Use a harder material and problem will be resolved? If they are correct, use of Bronze guides is not a long term solution!
My reading of that comment is it applies to the well known GM Service Spec of .0037 valve guide clearance shown in this picture:
Those are the specs used to determine whether or not to redo the guides or replace the heads. As you can see the max production line spec is ~ .0011-.0013 less than the max Service Spec depending on whether you are talking about an exhaust or intake valve.
You don't get valve drops until the clearance gets way above the .0037 number. If you have the heads apart and get measurements above .0037 GM says to fix the issue. If the heads are on the engine and not disassembled you get into another question of whether or not you should do anything if the measurement is .0038. The problem is reading the clearances on a fully assembled head on an engine in the engine compartment (the so called wiggle test). It isn't easy to set up the equipment and ensure the accuracy of the measurements.
There is no definitive data that proves excessive valve guide clearances caused the rash of valve drops that were reported on this forum 4 and 5 years ago. It is only a theory based on recommendations from various shops and a GM acknowledgement that a certain range of production heads had a machining problem.
At the time there were all sorts of theories about why the valves were dropping including aftermarket cams, aftermarket rocker arms with different ratios than stock, the stock exhaust valve design and build, etc. The problem is although 9 out of 10 failures were due to dropped exhaust valve heads there were some intake failures as well so the exhaust valve theory didn't quite fit. The aftermarket parts theory didn't quite fit either since a lot of the engines that failed had stock valve systems. Then we had the guide clearance theory which has some issues as well. First, the percentage of loose intake guides reported is much higher than the percentage of reported failed intake valves (that may be because the intake valve is a solid valve). Second, there are no definitive answers on how loose a guide has to be to actually cause a valve head to break off. My engine builder said he had worked with a lot of LS heads in the $40K+ 9000 rpm race engines that he builds and had never seen or heard of an LS engine issue due to loose guides. He said those kinds of engines don't come with warranties but the people who spend that kind of money for an engine do tend to get upset if one comes apart for something that might be considered a build or design error. His biggest bug a boo was the race team that bought one of those engines and at the end of the racing season let it sit till they hit the track again the next spring and tried to run it at 9K rpm and blew the engine. The usual cause was the valve springs weakening thus not being able to sustain that rpm level any more which led to pistons and valves colliding. The teams that threw on a fresh set of springs usually didn't have any problems. His experience led him to believe even on street engines if you have valve heads breaking off you need to look at the springs first.
I know the head of the exhaust valve on my engine went into the intake manifold. What I don't know is whether it hit the piston due to a weakened valve spring while running at 6800 to 7000 rpm for the umpteenth time, a valve guide had excessive clearance (there was no noise or excessive oil consumption) or the exhaust valve failed due to a poor design/build. The resulting fix coming out of all that is redo the guides (with bronze/PM), install solid SS valves which on the face of things looks like it is a guess that is trying to cover several possible causes of the failure.
As for GM addressing the problem they addressed a fair number of engine failures by replacing the engines under warranty. Out of 9 failures I personally knew about GM replaced 8 of the engines. The 9th had several engine mods including a cam, headers and a tune and the owner never asked them to cover the problem. As far as I am concerned they stepped up to the problem and did the right thing and did it multiple times.
We are here because of engine failures caused by valve drops not because of loose guides. Saying GM is ignoring the loose guide issue is ridiculous since there is no proof that loose guides were the cause of the initial rash of valve drops or the few that are being reported now. Yes, some of the failed engines did have loose guides as we have seen in various videos but we don't know what other things may have been going on at the same time. Some times we do get smoke where there is no fire and we get fire where there is no smoke. There is a lot of smoke around the valve guide clearance at this time and there isn't a lot of material to help you make an educated guess.
I am not bashing any of the other engine builders or machine shops that are offering solutions based on their experience that address what is definitely a Customer Concern issue. However, if loose guides are the real cause of dropped valves why is there a mixture of solutions? Why isn't fixing the guides properly the only solution? Why the insistence on replacing the stock exhaust valve with a solid ss valve? If the guides are the issue the valve shouldn't need to be replaced. That to me means the people recommending that solution are not sure about the cause of dropped valves and trying to cover as many possibilities as they can. If you trace the history of this discussion over the last 4 years you can see that lack of certainty all the way through.
Now here is my truth in lending statement. Early this year I was worried about the guides in my replacement engine (due to all of the hype). I had Peter Gibbons, Motorsports in Mooresville, NC remove the heads and check the valve guide clearances using a valve guide bore gauge to check the bores in 3 locations and a micrometer to measure the valve stem diameters. All valve stem diameters were within the production sped shown in the picture above. All but two intake guide clearances were within the .0037 spec and two were measured at .0039. No exhaust valve guide clearance was out of spec or close to being out of spec. This was after ~13K miles with about 4K of them being high rpm wide open or close to wide open track miles.
GMPP looked at the data and Peter's shop and approved replacing the heads due to the two intake guides being out slightly out of spec. Peter said the new stock heads were fine for the street and doing a few track days but If I thought I would be doing a lot of track days then I should look at increasing the reliability of the valve system. Those comments and suggestions that Jason at Katech made based on my engine usage led me to have the heads modified with bronze guides and Ti/Mo intake and exhaust valves.
I got the car back at the end of April and since then I have put about 500 miles of track usage (7 track days) on the engine with multiple trips to the 6800 to 6900 rpm level with no issues. I will be going back to Peter early next year to have him check the valve springs before I head out for more track days.
As Peter told me when he reported his initial findings, "You can more than likely just reassemble the heads and have no concerns." My problem I was stuck in a situation where GM's service guidance says to replace a head where the clearance is above .0037, the heads were apart and now was the time to do something Vs reassembling or installing the new stock heads. It took me several weeks to make up my mind. It wasn't as easy as when replacing a clutch pressure plate you say while I am in there I am going to replace everything due to the effort required to take everything apart and put it back together again.
I might have been better off not doing a damned thing, never having the heads checked and driving the car since I still have close to three years of GMPP no deductible coverage left.
Before you decide what to do recognize this isn't a clear cut situation. There may not be a problem to solve and if there is there are no clear cut solutions. Remember the old adage, Don't Fix it if it isn't Broken. Do your Due Diligence. Caveat Emptor.
Bill
Bill when it comes this this matter, I doubt that few have researched the information posted on it in here more thoroughly than myself.
Having said that, years ago, forum member hoefi, an engineer and a member here who successfully took GM to court over this matter, posted this information up with regard to what he called "stages" of guide wear, and where he predicted imminent failure would result if guide wear progressed to a certain point.
Long response Bill but I don't know if this explanation is what AH was referring which is why I asked for an clarification. My initial read of what AH meant about falling out of spec is a reference to the OEM guides not being hard enough in an LS 7 application. Use a harder material and problem will be resolved? If they are correct, use of Bronze guides is not a long term solution!
What I interpreted out of their statement was they were talking about a valve guide clearance falling out of spec Vs one that is in spec. There are a lot of stock valve guides that are well within GM specs.
Bill when it comes this this matter, I doubt that few have researched the information posted on it in here more thoroughly than myself.
Having said that, years ago, forum member hoefi, an engineer and a member here who successfully took GM to court over this matter, posted this information up with regard to what he called "stages" of guide wear, and where he predicted imminent failure would result if guide wear progressed to a certain point.
I remember that report. In your first link the info confirms info that Peter Gibbons told me the clearances have to be really large for a valve to fail. Hoefi's clearances were excessive compared to some of the results we are seeing in forum reported measurements. A fairly large number of the out of tolerance reports I have seen posted on the forum are no where near what his info indicates is a problem. I am going to take the liberty of quoting the post in this thread since it is important in the discussion. One thing about the report is that is a well documented report of one which is something that wasn't repeated very often so we have one really good data point of one which can be an issue when drawing conclusions. I tried to follow the same process when my reporting the results of my head story.
However, he didn't really win a case in court. Basically, GM decided it wasn't worth fighting the issue and gave up. That is an approved method of getting what you want.
My replacement engine heads had exhaust valve guide clearances that were well within the GM Spec Vs his at about the same mileage. The intake guides were the ones that were slightly out of tolerance.
Addressed in his report is some thinking about causes and he was looking at excessive guide clearances as being symptom of a deeper issue Vs the main cause of the failure. That report is what had me initially thinking of operating temps after my engine failed 4 years ago.
I really don't think we are any closer to knowing the true cause than we were then. If there are deeper issues then the guide material choice may be a big "So What." What is interesting is it looks like GM is going to put the engine in the ATS to make a super ATS-V so they have some faith in the engine.
Bill
Originally Posted by hoefi
Yes, service limit is 0.0037". Beyond that, exhaust valve stem will start to have problem getting rid of excess heat if the engine is driven really hard with long duration WOT. By the time clearance gets to around .007", galling will start to take place (as per evidence from my engine tear down inspection). From this point on, the valve stem is like a file and guide wear is really accelerated. My failed valve's corresponding guide clearance was 0.016". No valve will survive that type of clearance in my opionion. #1 exhaust is the broken valve.
Basically, there are three stages which leads up to a dropped valve scenario:
Stage 1 - factory clearance which somehow has abnormal high guide wear. Mine wore to the factory service limit (~.004") within 11,000 miles. Of that, there was only about 80 track miles. Six out of the eight exhaust guides are all sitting at this service limit. Stock engine, multiple oil changes during that period.
Stage 2 - Guide clearance between .004" to 0.007". If guide wear is dectected during this stage, it's only a matter in changing them out. I think so far, most of the excessive guide wear (with no dropped valve) are dectected druing this stage. During this stage, if the owner does not drive his car hard, the valve stem will most likely remain smooth and this stage could last long as the vehicle continues to gain mileage.
Stage 3 - Guide clearance between .007 to .015+". During this stage, any type of hard driving could easily induce material transfer on the valve stem. Once that takes place, stem becomes rough and galled. Accelerated wear will then take place regardless of how easy the owner drives his car afterwards. This stage won't last that long and once the guide clearance gets up to double digit thous, the valve head will eventually falls off.
Stage 2 and 3 are merely the end result of stage 1. The most troubled part is still understanding why stage 1 can happen so fast for some of the cars. For my own car, it could be due to excessive cold oil. Up until my valve dropped, most of the 11,000 miles I logged were short duration trips. The car was insured all year round and a lot of trips during the winter months were done in near freezing temperature (I am in Canada). I remember the oil would take easily 20 minutes to struggle up to 120 degrees. A lot of the trips were only 10 to 15 minutes long and the oil temp never went pass 100. I remember even a lot of the longer trips on the freeway, the oil never went pass 140 degrees. The high mileage LS7s we see on this board no doubt did not logged those miles doing 10 minute short trips. Having the car in warmer southern states don't hurt either. Storing the car for the winter also eliminates the cold short trips. The later ('09+ model) liquid/liquid oil cooler might be GM's way of correcting this issue. They might have reconized a potential problem there.
The trick to prevent a dropped valve is to try to catch the guide clearance during stage 2. Especially for owners who do a lot of short trips in cold regions and then would take their cars to the tracks during the weekends in the summer.
Last edited by Bill Dearborn; 07-11-2015 at 03:20 PM.
What I interpreted out of their statement was they were talking about a valve guide clearance falling out of spec Vs one that is in spec. There are a lot of stock valve guides that are well within GM specs.
Bill
Agreed. However, I believe AH is of the belief that oem guide material ( as well as Bronze) is not hard enough to prevent wear in the LS 7 application. Hence their recommendation for Moldstar 90.
But as you indicate a lot of stock valve guides are and stay within GM specs, which I find intriguing and a puzzlement for an explanation of what is causing the problem? Lot's of well intended theories but little facts!!
We have been saying for years that Bronze is the wrong material for the LS7 application (with stock rockers). That's why we use our proprietary Hardened Powder Metal valve guides. For those that want a more "exotic" alloy we offer our Moldstar90 Valve guides (which is superior to bronze in EVERY WAY).
We have reworked many many bronze and solid ss valved heads from aforementioned head rework shop. The bronze guides and solid ss valves is not the "fix" most are looking for.
Why use heavy solid ss valves when there are so many other options available. If the head falls out of spec its out of spec, all a solid ss valve is going to do is take longer to break. If everything on the head is done properly the head should not fall out of spec (anytime soon) and the thickness of the valve will not matter.
In our opinion adding a solid ss valve to the head is not the correct way to go and could even be viewed as a "crutch" of sorts.
i've checked stem thickness on these valves many times i've seen some as thin as .029 i'd never run a hollow valve in a high hp car. now the valve may not be the main cause but non the less with all the guide wear we're seeing on these cars and all the unclear results i wouldn't chance it. many other ppl wouldn't either after sliding in oil at 75mph on the interstate
Last edited by chadyellowz; 07-11-2015 at 03:51 PM.
There is no definitive data that proves excessive valve guide clearances caused the rash of valve drops that were reported on this forum 4 and 5 years ago. It is only a theory based on recommendations from various shops and a GM acknowledgement that a certain range of production heads had a machining problem.
and either is the theory that it doesn't...
This discussion is so circular it has become moronic. Excessive guide wear leads to valve failure. More so with a valve not meant to deal with being that much out of tolerance like the hollow OEM valve.
If you were talking solid valves I would say your probably safe at the spec limit. Probably.. roll the dice on that one. Your engine and money. But when it comes to the OEM valves running at the spec limit and thinking that amount of guide wear wont lead to failure, your making bad decision.
This discussion is so circular it has become moronic. Excessive guide wear leads to valve failure. More so with a valve not meant to deal with being that much out of tolerance like the hollow OEM valve.
If you were talking solid valves I would say your probably safe at the spec limit. Probably.. roll the dice on that one. Your engine and money. But when it comes to the OEM valves running at the spec limit and thinking that amount of guide wear wont lead to failure, your making bad decision.
I have never said excessive clearance didn't cause valve failure. The question is how much excessive clearance. You state if the exhaust valve was a solid valve there would be no problem but people are getting upset over intake guides not meeting spec.
Does a .0039 reading on an intake valve guide clearance mean that solid stem intake valve is going to fail? I doubt it. After several thousand miles of track usage and added thousands of street miles all of my valve stem diameters were within the production spec of .313 to .314 and all of the exhaust valve guides were fine. The so called weak sister exhaust valves were doing fine in that area. The only suspicious thing on the exhaust side was a thin burn line on the cylinder head that went from the spark plug hole to the exhaust valve seat on most of the cylinders.
There have been a fair number of similar readings reported on the forum where the intakes are out of tolerance and the exhausts are fine. All of the hype drove people to check the heads to find out there was no issue with the exhaust valve guide clearances which are the ones that fail most often. The fact there are reports like this casts a huge shadow of doubt on the theory the guides or the exhaust valve design are the major cause of the dropped valve problems. It only takes one result that doesn't fit a theory to prove the theory is incorrect. We have a lot more than one result.
It's been a while since I've posted here–mainly because work has kept me on writing projects having nothing to do with the LS7. Unfortunately, as much as I enjoy writing about my favorite engine, the feature tech writing I do about LS7 for that other web site is done for free and the fee jobs get priority.
That said, this week I'm back on the "LS7 beat" for a while.
I have enough miles on the set of heads on my engine which were a warranty replacement about a year ago that I can do the "modified wiggle test" I developed last Winter. That measurement procedure uses a test indicator rather than a dial indicator and is performed in a manner that eliminates having to use trig to correct for the distance above the top of the guide where a conventional dial measurement must be taken. It also eliminates any indicator mounting flex by bolting the indicator base to the rocker arm mounting boss.
While GM no longer accepts wiggle testing for warranty purposes, the fact remains that the only way to check stem-to-guide clearance with the heads on the engine is to use some form of "wiggling". My testing last Winter along with my visit to GM Powertrain earlier this year proved that the test indicator method was much more accurate than "classic" wiggle testing done with a dial indicator.
I'm going to perform the modified wiggle test this weekend.
After that, provided there are no problems–and I don't expect there to be any–I'm going to install an MSD Atomic Air Force intake manifold and test it.
In preparation for the manifold test, I baselined the car on Westech's chassis dyno last week and saw 453.7-rwhp and 423.0-rwt, both SAE-corrected. The only mods are:
my calibration
backdated 2011 exhaust
Lingenfelter 170° thermostat and straight water coolant
MSD coils
Denso IT-22 plugs
Red Line 10W30 in the engine, Red Line Superlight Shockproof in the trans and Red Line Heavy Shockproof in RDI
In a couple weeks, I go back to Westech with the MSD manifold on the engine.
It's been a while since I've posted here–mainly because work has kept me on writing projects having nothing to do with the LS7. Unfortunately, as much as I enjoy writing about my favorite engine, the feature tech writing I do about LS7 for that other web site is done for free and the fee jobs get priority.
That said, this week I'm back on the "LS7 beat" for a while.
I have enough miles on the set of heads on my engine which were a warranty replacement about a year ago that I can do the "modified wiggle test" I developed last Winter. That measurement procedure uses a test indicator rather than a dial indicator and is performed in a manner that eliminates having to use trig to correct for the distance above the top of the guide where a conventional dial measurement must be taken. It also eliminates any indicator mounting flex by bolting the indicator base to the rocker arm mounting boss.
While GM no longer accepts wiggle testing for warranty purposes, the fact remains that the only way to check stem-to-guide clearance with the heads on the engine is to use some form of "wiggling". My testing last Winter along with my visit to GM Powertrain earlier this year proved that the test indicator method was much more accurate than "classic" wiggle testing done with a dial indicator.
I'm going to perform the modified wiggle test this weekend.
After that, provided there are no problems–and I don't expect there to be any–I'm going to install an MSD Atomic Air Force intake manifold and test it.
In preparation for the manifold test, I baselined the car on Westech's chassis dyno last week and saw 453.7-rwhp and 423.0-rwt, both SAE-corrected. The only mods are:
my calibration
backdated 2011 exhaust
Lingenfelter 170° thermostat and straight water coolant
MSD coils
Denso IT-22 plugs
Red Line 10W30 in the engine, Red Line Superlight Shockproof in the trans and Red Line Heavy Shockproof in RDI
In a couple weeks, I go back to Westech with the MSD manifold on the engine.
I'm sure most will be interested in Wiggle results Hib. How many miles on the heads?
Does it really matter how hard the guides are? If so make them out of tungsten carbide then that would fix everything. Maybe a harder guide is just a crutch, they have been using bronze guides for a long time and no problems. If they are getting proper oil the valve shouldn't be hitting the guide like the rods, crank, and cam there is a thin layer of oil between the two. How hard are the crank cam and rod bearing material vs the crank rods and cam. American Heritage, what is the proof that bronze guides are wrong. You can keep putting harder and harder guides in until they don't wear but then the valve stem will start to wear if there is lack of oil to the guides.
07-10-2015, 03:25 AM
