[Z06] LS7 Engine problems
11-01-2007, 05:42 PM
#41
11-01-2007, 06:45 PM
#42
Drifting
[QUOTE=Foosh;1562563753]This is exactly the point, and a very good one. As a "self-proclaimed" (quoting Code Black), and actual scientist (I'll spare you the details on my credentials), the point is that it is impossible to tell what the actual percentage is from reports on this forum. However, there is fairly compelling circumstantial evidence to strongly suggest it is likely a rather small percentage.
A failure rate approaching 10% (just pulling a number out of a hat) would logically precipitate a campaign by GM for the sake of cost effectiveness. Moreover, we know from the Wixom builders that their max capacity is about 8,000 hand-built LS7s annually, which is close to the number of cars manufactured. If the failure number were anywhere near 10%, they'd need to be building a whole bunch of extra engines.
By way of illustration, a popular CF theory is that the valve springs are weak and this is causing an inordinate number of failures. If that were actually the case, it would be far more cost effective for GM to replace all valve springs, than it would be for them to replace 10-15% of failed LS7s. At mininum, one would have to ask why the valve spring design has not been modified in later engines, if the failure rate were so high? Wouldn't that be a "cheap fix?"
In addition, we never know how many of these cars are modified, and we have no clue how these cars have been used. Various polls posted here within the last few months have suggested a very high self-reported percentage of tunes, headers, intakes, etc. from CF Z06 forum dwellers. That is likely not a good representation of the general population of Z06 owners, and this forum is, no doubt, heavily over-represented with "hardcore" performance types.
When you are in a situation with nothing more than anecdotal reports to go on, and you have multiple, unknown variables, it is impossible to draw any conclusions, but you can make some logical inferences.
We really have no clue how many Z06 owners visit here. In addition, many of the "15" (or whatever number it is) reported failures here are from people reporting, "I know a friend of a friend whose engine melted down," or "my dealer told me........" In short, there is virtually no reliable documentation on this issue.[/QUOTE
your name was never brought up by me so kindly keep me out of your personal crusade
A failure rate approaching 10% (just pulling a number out of a hat) would logically precipitate a campaign by GM for the sake of cost effectiveness. Moreover, we know from the Wixom builders that their max capacity is about 8,000 hand-built LS7s annually, which is close to the number of cars manufactured. If the failure number were anywhere near 10%, they'd need to be building a whole bunch of extra engines.
By way of illustration, a popular CF theory is that the valve springs are weak and this is causing an inordinate number of failures. If that were actually the case, it would be far more cost effective for GM to replace all valve springs, than it would be for them to replace 10-15% of failed LS7s. At mininum, one would have to ask why the valve spring design has not been modified in later engines, if the failure rate were so high? Wouldn't that be a "cheap fix?"
In addition, we never know how many of these cars are modified, and we have no clue how these cars have been used. Various polls posted here within the last few months have suggested a very high self-reported percentage of tunes, headers, intakes, etc. from CF Z06 forum dwellers. That is likely not a good representation of the general population of Z06 owners, and this forum is, no doubt, heavily over-represented with "hardcore" performance types.
When you are in a situation with nothing more than anecdotal reports to go on, and you have multiple, unknown variables, it is impossible to draw any conclusions, but you can make some logical inferences.
We really have no clue how many Z06 owners visit here. In addition, many of the "15" (or whatever number it is) reported failures here are from people reporting, "I know a friend of a friend whose engine melted down," or "my dealer told me........" In short, there is virtually no reliable documentation on this issue.[/QUOTE
your name was never brought up by me so kindly keep me out of your personal crusade
11-01-2007, 07:51 PM
#43
[QUOTE=CodeBlack;1562569865]
Alrighty, then.
This is exactly the point, and a very good one. As a "self-proclaimed" (quoting Code Black), and actual scientist (I'll spare you the details on my credentials), the point is that it is impossible to tell what the actual percentage is from reports on this forum. However, there is fairly compelling circumstantial evidence to strongly suggest it is likely a rather small percentage.
A failure rate approaching 10% (just pulling a number out of a hat) would logically precipitate a campaign by GM for the sake of cost effectiveness. Moreover, we know from the Wixom builders that their max capacity is about 8,000 hand-built LS7s annually, which is close to the number of cars manufactured. If the failure number were anywhere near 10%, they'd need to be building a whole bunch of extra engines.
By way of illustration, a popular CF theory is that the valve springs are weak and this is causing an inordinate number of failures. If that were actually the case, it would be far more cost effective for GM to replace all valve springs, than it would be for them to replace 10-15% of failed LS7s. At mininum, one would have to ask why the valve spring design has not been modified in later engines, if the failure rate were so high? Wouldn't that be a "cheap fix?"
In addition, we never know how many of these cars are modified, and we have no clue how these cars have been used. Various polls posted here within the last few months have suggested a very high self-reported percentage of tunes, headers, intakes, etc. from CF Z06 forum dwellers. That is likely not a good representation of the general population of Z06 owners, and this forum is, no doubt, heavily over-represented with "hardcore" performance types.
When you are in a situation with nothing more than anecdotal reports to go on, and you have multiple, unknown variables, it is impossible to draw any conclusions, but you can make some logical inferences.
We really have no clue how many Z06 owners visit here. In addition, many of the "15" (or whatever number it is) reported failures here are from people reporting, "I know a friend of a friend whose engine melted down," or "my dealer told me........" In short, there is virtually no reliable documentation on this issue.[/QUOTE
your name was never brought up by me so kindly keep me out of your personal crusade
A failure rate approaching 10% (just pulling a number out of a hat) would logically precipitate a campaign by GM for the sake of cost effectiveness. Moreover, we know from the Wixom builders that their max capacity is about 8,000 hand-built LS7s annually, which is close to the number of cars manufactured. If the failure number were anywhere near 10%, they'd need to be building a whole bunch of extra engines.
By way of illustration, a popular CF theory is that the valve springs are weak and this is causing an inordinate number of failures. If that were actually the case, it would be far more cost effective for GM to replace all valve springs, than it would be for them to replace 10-15% of failed LS7s. At mininum, one would have to ask why the valve spring design has not been modified in later engines, if the failure rate were so high? Wouldn't that be a "cheap fix?"
In addition, we never know how many of these cars are modified, and we have no clue how these cars have been used. Various polls posted here within the last few months have suggested a very high self-reported percentage of tunes, headers, intakes, etc. from CF Z06 forum dwellers. That is likely not a good representation of the general population of Z06 owners, and this forum is, no doubt, heavily over-represented with "hardcore" performance types.
When you are in a situation with nothing more than anecdotal reports to go on, and you have multiple, unknown variables, it is impossible to draw any conclusions, but you can make some logical inferences.
We really have no clue how many Z06 owners visit here. In addition, many of the "15" (or whatever number it is) reported failures here are from people reporting, "I know a friend of a friend whose engine melted down," or "my dealer told me........" In short, there is virtually no reliable documentation on this issue.[/QUOTE
your name was never brought up by me so kindly keep me out of your personal crusade
11-01-2007, 11:14 PM
#44
Cruising
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I read an article, that was explaining why the Boeing 787 is behind schedual so much. Its the sub standard parts they have been getting from all the other countrys that are in the program.
The problem with us consumers is we get stuck with the junk we purchase that has the sub standard parts in it. I think this is the case with lots of so called "American made" cars. The needles are most likely dropping out of those rockers because some under paid mexican or ? what ever country didn't give a hoot, just like the 787 parts.
Yeah Joe engine assembler could have goofed too, or its a simple material defect, but I'm betting on just plain old sub standard junk parts, you know like all the other junk we are getting from China.
Many times the package says, "Assembled in USA" yet all the parts came from who knows where. And since alot of our good old steel foundrys and such have been legislated out of existance manufactures go to places like China for forgings and castings, then machine it here in the US, problem is, whats in that casting or forging? Could this by why an expensive Titanium Connecting Rod fails? I would like to know where are these parts and the metals made and the process to make them?
The problem with us consumers is we get stuck with the junk we purchase that has the sub standard parts in it. I think this is the case with lots of so called "American made" cars. The needles are most likely dropping out of those rockers because some under paid mexican or ? what ever country didn't give a hoot, just like the 787 parts.
Yeah Joe engine assembler could have goofed too, or its a simple material defect, but I'm betting on just plain old sub standard junk parts, you know like all the other junk we are getting from China.
Many times the package says, "Assembled in USA" yet all the parts came from who knows where. And since alot of our good old steel foundrys and such have been legislated out of existance manufactures go to places like China for forgings and castings, then machine it here in the US, problem is, whats in that casting or forging? Could this by why an expensive Titanium Connecting Rod fails? I would like to know where are these parts and the metals made and the process to make them?
11-02-2007, 04:50 AM
#46
Pro
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engguy, thats a great point. The rockers are a perfect illustration a substandard part.
I would think that GM determined that no major damage will result and the mean failure rate was such that it was cheaper to just pay the labor to pull the pan to pull out needles and replace the effected rockers then the difference in a change contract to resupply.
I dont beleive LS7's are having rod problems, but like I said, the one thread out their is putting a bunch of folks panties in a twist. I dont think its legit to take that one instance and parralel it to the known rocker problem to jump to the conclusion they must have rod problems as we dont know what happened in that one case. They could very well have had out of tolerance bearings or simply not torqued the rod bolts.
Time will tell.
I would think that GM determined that no major damage will result and the mean failure rate was such that it was cheaper to just pay the labor to pull the pan to pull out needles and replace the effected rockers then the difference in a change contract to resupply.
I dont beleive LS7's are having rod problems, but like I said, the one thread out their is putting a bunch of folks panties in a twist. I dont think its legit to take that one instance and parralel it to the known rocker problem to jump to the conclusion they must have rod problems as we dont know what happened in that one case. They could very well have had out of tolerance bearings or simply not torqued the rod bolts.
Time will tell.
11-02-2007, 06:25 AM
#47
Burning Brakes
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I'm just curious what is failing on them. I mentioned in another post, the person doing the assembly is the least likely cause. Though humans can goof up. I would first blame the origin of the parts involved.
I would like to know from the builders that frequent this site what kind of checks they are doing in the process? Do the parts come to you in a tray and you just put it together or are there certain checks that are done other than fastener torques?
I would like to know from the builders that frequent this site what kind of checks they are doing in the process? Do the parts come to you in a tray and you just put it together or are there certain checks that are done other than fastener torques?
In the event there was an issue with bad bearings, it wouldn't be 15 cars in 3 years, rather an entire VIN range/serial number series.
A large percentage of aircraft mishaps are due to pilot/human error.
A super charger isn't going to cause the motor to pop for not good reason. However an improper air/fuel mixer will certainly ruin your day.
Just my $.02
11-02-2007, 08:22 AM
#48
Race Director
11-02-2007, 11:32 AM
#49
Burning Brakes
11-02-2007, 03:00 PM
#50
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The idea thats been alluded to in other ways, but not put so eliquently as he did.
That guys are seeing a few cases and jumping to conclusions implying its a disproportionately high failure rate without knowing the full population size.
Knowing only x number of failures without knowing the denominator makes it impossible to draw a valid conclusion.
The way I put that is, you see it on the net so a very small number gets blown way out of proportion since it so visable and gets so many in a big to do. Throw in pictures, if they had any, like the rocker needles, then Oh crap!! Every one is gonna start splitting needles.
On the internet Pictures lead to the formula:
Actual_number X (Number_of_pictures X 1000)
That guys are seeing a few cases and jumping to conclusions implying its a disproportionately high failure rate without knowing the full population size.
Knowing only x number of failures without knowing the denominator makes it impossible to draw a valid conclusion.
The way I put that is, you see it on the net so a very small number gets blown way out of proportion since it so visable and gets so many in a big to do. Throw in pictures, if they had any, like the rocker needles, then Oh crap!! Every one is gonna start splitting needles.
On the internet Pictures lead to the formula:
Actual_number X (Number_of_pictures X 1000)
11-02-2007, 06:41 PM
#51
The Consigliere
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I agree. And by the way, the attempted knock earlier in the series of posts on this topic on supposed 1950s tech - anybody thought about how long overhead cam engines have been around? As long as OHV engines, and today there are still OHC engines breaking belts, chewing valves etc.
Simply put OHV designs are no more old tech than OHC
Simply put OHV designs are no more old tech than OHC
11-02-2007, 07:23 PM
#52
Burning Brakes
I agree. And by the way, the attempted knock earlier in the series of posts on this topic on supposed 1950s tech - anybody thought about how long overhead cam engines have been around? As long as OHV engines, and today there are still OHC engines breaking belts, chewing valves etc.
Simply put OHV designs are no more old tech than OHC
Simply put OHV designs are no more old tech than OHC
The point of bringing up the 1950's was to show the amount of experience with a pushrod motor; not a reference to old technology. I would rather have a pushrod motor than a supposed high tech OHC motor that weighs twice as much. There are advantages of the OHC though....The ability to change valve timing for horsepower in the upper RPM range and keep great idle quality and low RPM cruising is one of them.
11-02-2007, 07:57 PM
#53
I dont care what you guyz are saying over here, many of you CF forum members cry if you once get close to the 7000 RPM rev-limiter, its called the rev-limiter because anything beyond that is dangerous, you should be able to have fun with everything at and below that point. I am not asking you to cruise at 7000 RPMs, but for cars like mines that sees that rev limiter on a daily basis infact 50 times daily, those valve-springs sure need to be replaced. two friends of mine replaced engines because of valve-spring failure, the other guy replaced his second engine again because of the same valve-spring failure.
There are currently two cars at the dealership with engine failures due to broken valve springs, I am surprized how some members dont want to agree that this is a serious problem. I might have been lucky for 26,000 Miles, however I am sending Carlos a payment in a few hours for aftermarket valve-train components, that would otherwise be installed with an aftermarket camshaft for added safety, I know mines are going to break anytime.
There are currently two cars at the dealership with engine failures due to broken valve springs, I am surprized how some members dont want to agree that this is a serious problem. I might have been lucky for 26,000 Miles, however I am sending Carlos a payment in a few hours for aftermarket valve-train components, that would otherwise be installed with an aftermarket camshaft for added safety, I know mines are going to break anytime.
11-02-2007, 08:22 PM
#54
I dont care what you guyz are saying over here, many of you CF forum members cry if you once get close to the 7000 RPM rev-limiter, its called the rev-limiter because anything beyond that is dangerous, you should be able to have fun with everything at and below that point. I am not asking you to cruise at 7000 RPMs, but for cars like mines that sees that rev limiter on a daily basis infact 50 times daily, those valve-springs sure need to be replaced. two friends of mine replaced engines because of valve-spring failure, the other guy replaced his second engine again because of the same valve-spring failure.
There are currently two cars at the dealership with engine failures due to broken valve springs, I am surprized how some members dont want to agree that this is a serious problem. I might have been lucky for 26,000 Miles, however I am sending Carlos a payment in a few hours for aftermarket valve-train components, that would otherwise be installed with an aftermarket camshaft for added safety, I know mines are going to break anytime.
There are currently two cars at the dealership with engine failures due to broken valve springs, I am surprized how some members dont want to agree that this is a serious problem. I might have been lucky for 26,000 Miles, however I am sending Carlos a payment in a few hours for aftermarket valve-train components, that would otherwise be installed with an aftermarket camshaft for added safety, I know mines are going to break anytime.
People spend more money on a racing engine than you spent on the entire car, and hope it lasts one weekend living at redline. I don't know how you would expect an engine warrantied for 5/100K to hit redline 50 times a day for the price you paid.
11-02-2007, 09:31 PM
#55
I would certainly agree with the part of your statement that I highlighted above, but that's about it. If what you say about your use is true, I would say it is a remarkable testament to the robustness of the engine that you made it to 26K miles.
People spend more money on a racing engine than you spent on the entire car, and hope it lasts one weekend living at redline. I don't know how you would expect an engine warrantied for 5/100K to hit redline 50 times a day for the price you paid.
People spend more money on a racing engine than you spent on the entire car, and hope it lasts one weekend living at redline. I don't know how you would expect an engine warrantied for 5/100K to hit redline 50 times a day for the price you paid.
for a modification that costs "nothing", better valve-springs cost nothing man, and for that zero added cost, I think it was a must. Ive heard of at least 10 engines with valve-spring failures, if the springs were stronger, I wouldn't have heard of those 10
11-02-2007, 09:53 PM
#56
Specially since he's got the following mods:
Vortech Supercharged Z06, Stage 1 brake package, Spec 2+ Clutch & alum. flywheel, catless Kooks headers/midpipe, custom designed exhaust with exhaust butterflies, B&M short-shifter, 345 Nitto Invos, and a few gauges (wideband/ boost).
Ayousef, how many of the failures you mention were with stock trim?
Still, even though mines stock, I'll probably be upgrading the springs/rockers myself once out of warranty, since I track it and it's cheap insurance.
11-02-2007, 10:01 PM
#57
Specially since he's got the following mods:
Nothing wrong with mods though! It just shows that GM has allowed sufficient tolerances/robustness for modest mods and some "spirited" use.
Ayousef, how many of the failures you mention were with stock trim?
Still, even though mines stock, I'll probably be upgrading the springs/rockers myself once out of warranty, since I track it and it's cheap insurance.
again and again, for a "priceless" valvespring mod to the LS7, I think we would have heard of much less engines that had to be replaced.
What you're doing is a good mod.
11-02-2007, 11:18 PM
#58
Safety Car
I would think GM looked hard at the components mentioned. I had two LS6’s let go with broken valve springs, one @ 22,000 miles and one @ 55 thousand miles. 14k on the LS7 so far. It really burns much less oil that the LS6 and LS2s I owned and ruins a lot cooler oil temps. We are their ultimate test mules.
Doc E.
Doc E.
11-03-2007, 11:52 AM
#59
Hey man regardless of the price, the car wasn't sold stating "this is an affordable car and if you make it to the redline more than a few times, you will end up with a blown up engine". My car is not a car that lives on the redline, infact you spend VERY little time "close" to the redline in a 2nd gear blast for example. Simply if the car couldnt handle the 7000 RPM limiter it should have been lower stock period.
for a modification that costs "nothing", better valve-springs cost nothing man, and for that zero added cost, I think it was a must. Ive heard of at least 10 engines with valve-spring failures, if the springs were stronger, I wouldn't have heard of those 10
for a modification that costs "nothing", better valve-springs cost nothing man, and for that zero added cost, I think it was a must. Ive heard of at least 10 engines with valve-spring failures, if the springs were stronger, I wouldn't have heard of those 10
Engines are built according to "normal use" for the particular car. This is a car built primarily for street use, and occasional, spirited use, track days, but primarily as a street car.
If you want a more "race-prepped" and hardened engine, go to Katech, and get out your check book. The cost to do that is far more than most Corvette owners are willing to pay, and completely unnecessary given their use. It is, however, great, race-proven technology, stronger than the stock engine, and worth the greatly increased cost if that is your intended use.
The design and engineering of all engines is based upon average use, and a cost vs. benefit analysis. It is also a marketing decision based upon what price the market is willing to support for a given model.
However, back to valve springs.............like others, you are incorrectly assuming that valve springs are absolutely, positively, no doubt about it, scientifically proven to be the cause of an abnormal number of LS7 engine failures. As I tried to suggest above in this thread, if that were the case, it would be a no-brainer for GM to put in a different and stronger valve spring design, since it is, as you suggest, a relatively cheap fix compared to replacing a bunch of engines under warranty. I ask again, if valve springs are a known weak spot and cause of numerous failures, why haven't they been changed in later models?
I seriously doubt that more than 200-300 Z06s sold in both the 06-07 model years have seen more than 4-5 track days a year. You simply don't build 14,000 cars for an application experienced by a few hundred cars.
Last edited by Foosh; 11-03-2007 at 12:00 PM.
11-03-2007, 02:53 PM
#60
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Honestly its a tear. I am on board with the % not being huge, but it seems to me they could have beefed up the top end all things considered.
The marketing and history of the model implies its intended for track use. To me, if you put oil level adjustments in the manual for track days, you are indicating that is an expected use for the vehicle. Marketing the car with dry sump as a feaure for sustained high G is a kicker too. As such it should be a design consideration that the engine will see redline frequently.
The whole BS visor swap from Homelink to Lear says to me they will pinch pennies on components, and are OK with the idea that for a % of users the components just wont work.
True that is not exactly comparible as an engine is a huge warranty expense, however, they also know they will deny it under the 'abuse' get of of jail free clause.
The bean counters are this cars worst enemy. I want to say I dont think they use substandard bits intentionally, but I dont think the jury is in on this. They no doubt may have looked at how many cases they had, looked at the different to resupply beefier bits versus warrenty, they looked at how many they were able to successfully deny under the abuse clause. I would love to see the math, but GM will never share that.
Bottom line, the car is pretty tough, normal uses with occasion bad boy behavior will be OK, but routine hard use is asking for trouble.
The marketing and history of the model implies its intended for track use. To me, if you put oil level adjustments in the manual for track days, you are indicating that is an expected use for the vehicle. Marketing the car with dry sump as a feaure for sustained high G is a kicker too. As such it should be a design consideration that the engine will see redline frequently.
The whole BS visor swap from Homelink to Lear says to me they will pinch pennies on components, and are OK with the idea that for a % of users the components just wont work.
True that is not exactly comparible as an engine is a huge warranty expense, however, they also know they will deny it under the 'abuse' get of of jail free clause.
The bean counters are this cars worst enemy. I want to say I dont think they use substandard bits intentionally, but I dont think the jury is in on this. They no doubt may have looked at how many cases they had, looked at the different to resupply beefier bits versus warrenty, they looked at how many they were able to successfully deny under the abuse clause. I would love to see the math, but GM will never share that.
Bottom line, the car is pretty tough, normal uses with occasion bad boy behavior will be OK, but routine hard use is asking for trouble.