[Z06] Valve guide wear root cause found!
08-15-2012, 09:56 PM
#1
Le Mans Master
Thread Starter
Valve guide wear root cause found?
Originally Posted by C5 Hardtop
After 33 days with my 08 Z in the shop, I got it back today 
The Z had broken rockers, very excessively worn valves and valve guides and a damaged cam.
While discussing the work completed with the service manager, his response to "How many miles before this happens again?" was, "it probably won't happen again."
He went into detail describing why which consisted of the discussion he had with the regional GM engineer who came to look at my car. The root cause was the heads were milled wrong where the rocker arms are mounted. This caused the rocker to come down at an angle which in turn pushed the valve down wrong which in turn made the valve stem and valve guide wear out prematurely.
So the GM engineer prescribed brand new heads (that are milled correctly). A new cam went in, new valve springs, new valves and valve guides were installed. The valve train is noticeably quieter now (comparing sound prior to failure).
Interestingly, the dealership does not have access to the same problem database that the regional engineer has.
The service manager at Lee Johnson was very thorough and test drove the car after the initial GM suggestion to only replace the broken rockers and cam. He found the problem still existed and pursued until satisfied. Hat’s off to Jeff and his department. When the GM customer survey arrives regarding my service, they get all high marks and a phone call letting them know I gave them an A grade.
The Z had broken rockers, very excessively worn valves and valve guides and a damaged cam.While discussing the work completed with the service manager, his response to "How many miles before this happens again?" was, "it probably won't happen again."
He went into detail describing why which consisted of the discussion he had with the regional GM engineer who came to look at my car. The root cause was the heads were milled wrong where the rocker arms are mounted. This caused the rocker to come down at an angle which in turn pushed the valve down wrong which in turn made the valve stem and valve guide wear out prematurely.
So the GM engineer prescribed brand new heads (that are milled correctly). A new cam went in, new valve springs, new valves and valve guides were installed. The valve train is noticeably quieter now (comparing sound prior to failure).
Interestingly, the dealership does not have access to the same problem database that the regional engineer has.
The service manager at Lee Johnson was very thorough and test drove the car after the initial GM suggestion to only replace the broken rockers and cam. He found the problem still existed and pursued until satisfied. Hat’s off to Jeff and his department. When the GM customer survey arrives regarding my service, they get all high marks and a phone call letting them know I gave them an A grade.
I've always suspected it was a quality control issue, not a design flaw.
Bad news is that just replacing the guides with bronze and ss valves won't fix the root cause.
Last edited by AirBusPilot; 08-16-2012 at 12:24 AM.
08-15-2012, 10:01 PM
#3
http://forums.corvetteforum.com/c6-z...-restored.html
I've always suspected it was a quality control issue, not a design flaw.
Bad news is that just replacing the guides with bronze and ss valves won't fix the root cause.
I've always suspected it was a quality control issue, not a design flaw.
Bad news is that just replacing the guides with bronze and ss valves won't fix the root cause.
08-15-2012, 10:06 PM
#5
Le Mans Master
Thread Starter
Those that were stating bad geometry were on the right track, but with a wrong conclusion (design flaw).
This would be a very hard problem to figure out (obviously), even for GM, since it is so inconsistent.
Ricky, it's cleaned out now.
This would be a very hard problem to figure out (obviously), even for GM, since it is so inconsistent.
Ricky, it's cleaned out now.
08-15-2012, 10:11 PM
#7
Le Mans Master
Thread Starter
08-15-2012, 10:14 PM
#8
Instructor
08-15-2012, 10:15 PM
#9
Drifting
Wow this is great news. Wonder when they discovered this and made the fix on production heads? I just bought a gmpp 36/36 on my 09Z because I had some concern about this and figured a extended warranty and leaving it stock would take away the worry. Now, if this is all true, I may just have to do a little modding!
And by the way, I also have a 02Z cam/header/intake car with 110K on the clock thats still on the original clutch and heads never been off. These cars are truly amazing!
And by the way, I also have a 02Z cam/header/intake car with 110K on the clock thats still on the original clutch and heads never been off. These cars are truly amazing!
08-15-2012, 10:17 PM
#10
Le Mans Master
Thread Starter
08-15-2012, 10:17 PM
#11
Yeah, this is interesting news, and I had read the original poster's comments earlier.
If what he is saying does turn out to be true then a number of points will need to be addressed.
I wonder how does one tell if the heads they have are milled correctly or not.
08-15-2012, 10:17 PM
#12
Le Mans Master
Great News
08-15-2012, 10:18 PM
#13
Burning Brakes
At any rate, if that is the root cause, I guess the next step is how to figure out if someone has a properly milled head or not.
08-15-2012, 10:20 PM
#15
Le Mans Master
Thanks.
Yeah, this is interesting news, and I had read the original poster's comments earlier.
If what he is saying does turn out to be true then a number of points will need to be addressed.
I wonder how does one tell if the heads they have are milled correctly or not.
Yeah, this is interesting news, and I had read the original poster's comments earlier.
If what he is saying does turn out to be true then a number of points will need to be addressed.
I wonder how does one tell if the heads they have are milled correctly or not.
08-15-2012, 10:21 PM
#16
Le Mans Master
Thread Starter
Originally Posted by 06' Quicksilver Z06
Thanks.
Yeah, this is interesting news, and I had read the original poster's comments earlier.
If what he is saying does turn out to be true then a number of points will need to be addressed.
I wonder how does one tell if the heads they have are milled correctly or not.
Yeah, this is interesting news, and I had read the original poster's comments earlier.
If what he is saying does turn out to be true then a number of points will need to be addressed.
I wonder how does one tell if the heads they have are milled correctly or not.
08-15-2012, 10:23 PM
#17
i think there was a 2010 that dropped a valve...but doesnt mean the motor wasnt built sometime in 2009..or for that matter the heads were in stock since then
08-15-2012, 10:26 PM
#19
Burning Brakes
08-15-2012, 10:28 PM
#20
