Valve guide problems - LS3 vs LS7
12-21-2016, 10:57 PM
#1
Instructor
Thread Starter
Valve guide problems - LS3 vs LS7
I've been contemplating a return to the Corvette family after selling my 2009 Z51, CRM, NPP, Gumbies, A6 last year to a Forum member. This time I'm looking to step up to a Z06 or possible a 427 convertible. In reading all the conversations about the valve guide problems with the LS7, I'm wondering why the LS3 doesn't seem to have the same level of issues. Can someone explain this to me.
Regards,
Pat Terry
Regards,
Pat Terry
12-22-2016, 07:58 AM
#2
Race Director
Only thing I know is that GM stated that the 427 LS7 issue was from poor machining during production.
This did not concern the LS3 head work.
Also It seems to be more of a problem for the high rpm guys and usually shows itself early on.
This did not concern the LS3 head work.
Also It seems to be more of a problem for the high rpm guys and usually shows itself early on.
12-22-2016, 09:56 AM
#3
I'm not sure about this either, but it could be in part due to the fact that the LS7has a 1.8:1 rocker ratio vs. the 1.7:1 ratio on the LS3 motors, which translates into faster lift and more total lift (for the same lobe profile) and, consequently, more friction and load on the guide.
12-22-2016, 12:02 PM
#4
Team Owner
Ls7 has completely different head casting and design.
1.8 rockers
Larger 2 piece sodium filled exhaust valves
Larger more aggressive cam
Higher RPM
Combine all that, and LS7 is a recipe for disassater until it is fixed. Ls3s do wear guides, but the valves are much more robust so the odds of motor grenading is far lower.
That being said, it can happen on any car. My friends bone stock <10k mile ZL1 camaro with a LSA dropped a valve.
1.8 rockers
Larger 2 piece sodium filled exhaust valves
Larger more aggressive cam
Higher RPM
Combine all that, and LS7 is a recipe for disassater until it is fixed. Ls3s do wear guides, but the valves are much more robust so the odds of motor grenading is far lower.
That being said, it can happen on any car. My friends bone stock <10k mile ZL1 camaro with a LSA dropped a valve.
11-20-2018, 08:35 AM
#5
Are there any VIN numbers or head markings that can identify those that had bad machining per this article?
Like which Plant?
Like which Plant?
Corvette Owners: LS7 Engine Problems and the 'Wiggle Test'
https://www.thoughtco.com/ls7-engine...le-test-916184Last edited by Chad97z; 11-20-2018 at 08:37 AM.
11-20-2018, 09:29 AM
#8
I dont know. Maybe increased oil consumption. And if it is burning extra oil, it may set a code.
But, I'm more interested in identifying which corvettes were made at the Plant that had bad machining..
I'm looking at a z06.
But, I'm more interested in identifying which corvettes were made at the Plant that had bad machining..
I'm looking at a z06.
11-20-2018, 10:27 AM
#9
Safety Car
That article does not tell anywhere near the whole story. While the problem with the incorrectly machined LS7 heads is true, there is more to the issue. There are plenty of LS7 valve failures that have heads that were perfectly machined. Some people think that it is a combination of incompatible materials in the valve guides and the titanium valves. Some of the sodium filled exhaust valves did not have the proper amount of sodium in them which did not allow proper cooling of those valves, accelerating the wear. Improper surface coating smoothness on some of the valves which accelerated wear on the guides, and hollow sodium filled valves that had inconsistent wall thickness. Add to that the fact that half the rockers have an offset (intake valves, I think) which will put more side loading on those valves, a 1.8 rocker ratio which again puts more side stress on the valves and guides. I think at minimum GM should have gone with a roller tip rocker to alleviate some of the side loading.
My thinking is that if I were interested in an Z06, or any car with an LS7, I would want documentation that the heads were checked and in spec. I would also set up a regular schedule of checking the heads/valves/guides every several thousand miles (maybe at every oil change) to make sure everything was okay.
My thinking is that if I were interested in an Z06, or any car with an LS7, I would want documentation that the heads were checked and in spec. I would also set up a regular schedule of checking the heads/valves/guides every several thousand miles (maybe at every oil change) to make sure everything was okay.
11-20-2018, 01:12 PM
#10
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IIRC, all LS7 heads were machined at the same subcontracted company. Supposedly, a fixturing error was responsible for the initial few years of production, but even some of the heads that were "fixed" have failed a second time. Personally, I believe the dry sump system that was designed for track use, has played a big part in the failures, by extending the warmup time beyond the normal usage of the everyday casual Z06 driver.
11-20-2018, 02:11 PM
#11
Team Owner
That article does not tell anywhere near the whole story. While the problem with the incorrectly machined LS7 heads is true, there is more to the issue. There are plenty of LS7 valve failures that have heads that were perfectly machined. Some people think that it is a combination of incompatible materials in the valve guides and the titanium valves. Some of the sodium filled exhaust valves did not have the proper amount of sodium in them which did not allow proper cooling of those valves, accelerating the wear. Improper surface coating smoothness on some of the valves which accelerated wear on the guides, and hollow sodium filled valves that had inconsistent wall thickness. Add to that the fact that half the rockers have an offset (intake valves, I think) which will put more side loading on those valves, a 1.8 rocker ratio which again puts more side stress on the valves and guides. I think at minimum GM should have gone with a roller tip rocker to alleviate some of the side loading.
My thinking is that if I were interested in an Z06, or any car with an LS7, I would want documentation that the heads were checked and in spec. I would also set up a regular schedule of checking the heads/valves/guides every several thousand miles (maybe at every oil change) to make sure everything was okay.
My thinking is that if I were interested in an Z06, or any car with an LS7, I would want documentation that the heads were checked and in spec. I would also set up a regular schedule of checking the heads/valves/guides every several thousand miles (maybe at every oil change) to make sure everything was okay.
11-20-2018, 05:52 PM
#12
If the heads were done by a contractor, then what was all that touchy-feelie stuff when GM promoted that each ls7 had it's own engineer/mechanic and they even put their name on it.. makes me feel all warm and fuzzy, dont it you? Haha
11-20-2018, 10:53 PM
#14
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Don't confuse yourself by thinking that the final engine assembly work done in the Wixom plant, was the same place and the same people that did the forgings, the machining, the pre-assembly, and a host of other operations. Do a little research before you make dumb comments.
11-20-2018, 10:55 PM
#15
As a final assembler, and having your name placed on a Engine, I would think the guy should have checked everything over.. Tolerances and everything.. So maybe you should thinking about it... And what the hell do you know? Do you work for GM? The heads were not machined properly. That is proven. They should have been checked over by the assembler or whoever was the QA person. Boom. Done.
Don't confuse yourself by thinking that the final engine assembly work done in the Wixom plant, was the same place and the same people that did the forgings, the machining, the pre-assembly, and a host of other operations. Do a little research before you make dumb comments.
Last edited by Chad97z; 11-20-2018 at 11:02 PM.
11-21-2018, 01:01 PM
#17
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As a final assembler, and having your name placed on a Engine, I would think the guy should have checked everything over.. Tolerances and everything.. So maybe you should thinking about it... And what the hell do you know? Do you work for GM? The heads were not machined properly. That is proven. They should have been checked over by the assembler or whoever was the QA person. Boom. Done.