Ls7 heads dropping valves
03-05-2013, 03:49 PM
#61
The guides wear in a a bell pattern and it works the head of the valve until it breaks off. Unfortunately if the machining error exists it can happen with just normal driving.
03-06-2013, 06:04 AM
#62
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03-06-2013, 01:56 PM
#64
Actually it was valve guide to seat concentricity. The only way to truly measure is to take apart the heads and measure the clearance. Symptoms are noisy valvetrain and excessive oil consumption.
03-06-2013, 08:34 PM
#65
Thanks for clearing that up Jason, that seems more reasonable than the rocker pedestals. I'd assume it was a single point live pilot type seat and guide machine, rather than a dead pilot. Is the intake problematic as well or is it isolated to the exhausts only?
03-07-2013, 07:19 AM
#66
We've seen the intake also.
03-07-2013, 08:22 PM
#68
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I feel like I need to post to clarify something:
Myth#1: guides only wear on tracked cars--false
Myth#2: guide wear will have symptoms such as oil consumption or noise
Neither of those were the case with my 16,000 mile ls7 garage queen. The guides look worn enough to break the valve head off at any time.
http://m.youtube.com/#/watch?v=l4gkKpDNZ_E&feature=plcp
Myth#1: guides only wear on tracked cars--false
Myth#2: guide wear will have symptoms such as oil consumption or noise
Neither of those were the case with my 16,000 mile ls7 garage queen. The guides look worn enough to break the valve head off at any time.
http://m.youtube.com/#/watch?v=l4gkKpDNZ_E&feature=plcp
03-08-2013, 01:06 PM
#70
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Rebuild of the head with new valve guides and recutting the seats should fix it. Extra insurance with solid stainless valves and dual springs depending on your feeling about the stock valves.
03-10-2013, 01:25 AM
#71
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what percentage of LS7`s do you think are effected? so are you saying the valve guides are fine unless the valve seat is machined off center of the guide?
03-10-2013, 05:16 AM
#72
This really pushed me away from the C6Z06, which is sad because there are several very low mileage `06 and `07 Zs in my price range. I guess I'll stick with a `10+ GS.
03-10-2013, 01:26 PM
#73
I think on cf GM admitted to the machining issue late during the `12 model year and they were supposed to check all heads for the issue before building, in theory making `13s gtg (assuming the LS7 wasn't built in early `12). However, they also down played the issue stating the problem would pop up in the first few thousand miles, when it happens at random; and despite this being a known issue, effecting more cars than they care to admit, they will not issue a recall nor fix LS7s with this defect out side of warranty (yes, your `07 Z06 you bought brand new could have 10K miles, have the bad heads and your SOL). I mean I understand charging to inspect the head if the car is out of warranty, or in warranty but there's no symptoms; but if this defect is found and/or causes damage, take care of your customer.
This really pushed me away from the C6Z06, which is sad because there are several very low mileage `06 and `07 Zs in my price range. I guess I'll stick with a `10+ GS.
This really pushed me away from the C6Z06, which is sad because there are several very low mileage `06 and `07 Zs in my price range. I guess I'll stick with a `10+ GS.
Last edited by ramairws6; 03-24-2013 at 10:12 PM.
03-10-2013, 03:22 PM
#74
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I think on cf GM admitted to the machining issue late during the `12 model year and they were supposed to check all heads for the issue before building, in theory making `13s gtg (assuming the LS7 wasn't built in early `12). However, they also down played the issue stating the problem would pop up in the first few thousand miles, when it happens at random; and despite this being a known issue, effecting more cars than they care to admit, they will not issue a recall nor fix LS7s with this defect out side of warranty (yes, your `07 Z06 you bought brand new could have 10K miles, have the bad heads and your SOL). I mean I understand charging to inspect the head if the car is out of warranty, or in warranty but there's no symptoms; but if this defect is found and/or causes damage, take care of your customer.
This really pushed me away from the C6Z06, which is sad because there are several very low mileage `06 and `07 Zs in my price range. I guess I'll stick with a `10+ GS.
This really pushed me away from the C6Z06, which is sad because there are several very low mileage `06 and `07 Zs in my price range. I guess I'll stick with a `10+ GS.
Here's a link to my 09 which is making a ticking/tapping shound, definitely some kind of miss. Only 18k miles.
03-11-2013, 07:17 AM
#75
I have no idea what percentage. We'll probably never know. Yes, it's either machined wrong or it's not. If you don't have the problem early then you never will.
03-11-2013, 12:46 PM
#76
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Can you explain what kind of noise I should listen for? I know the injectors are noisy...I have stethoscoped the top half of the engine a few times but I also hear a consistant tick from the top of the valve covers too...I assume this is normal...and it does amplify with RPM..but the noise is consistent over the rpm range
03-11-2013, 12:58 PM
#77
Can you explain what kind of noise I should listen for? I know the injectors are noisy...I have stethoscoped the top half of the engine a few times but I also hear a consistant tick from the top of the valve covers too...I assume this is normal...and it does amplify with RPM..but the noise is consistent over the rpm range
03-23-2013, 11:30 PM
#78
This happened to my friend. He has an 07 ZO6 that had 28k on the clock last year when his exhaust valve broke. The carnage was impressive to say the least. The head of the exhaust valve broke off at 6500-7000rpm and the piston exploded out the side of the block.
03-23-2013, 11:40 PM
#79
TECH Resident
What sort of concentricity error in thou?