View Poll Results: My car is running fine (only vote if your LS7 is Ok)
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[Z06] How many are NOT having Valve issues ?
12-21-2013, 11:48 AM
#22
Team Owner
2006 w/ 27,000 miles. Stock heads. I do have a tune. Planning on doing heads this winter....if I don't get a C7.
12-21-2013, 11:52 AM
#23
Team Owner
Just because the car is running doesn't mean there isn't an issue. All the people who dropped a valve could say the same thing 1 mile before it happened. I know of 3-4 people locally that were running fine and would have said the same thing but when they pulled their heads they were all 3-5x out of spec. Does that mean they didn't have an issue?
12-21-2013, 11:58 AM
#24
Melting Slicks
Just because the car is running doesn't mean there isn't an issue. All the people who dropped a valve could say the same thing 1 mile before it happened. I know of 3-4 people locally that were running fine and would have said the same thing but when they pulled their heads they were all 3-5x out of spec. Does that mean they didn't have an issue?
Just because the valves have wiggle doesn't mean its going to fail. What is the threshold of wiggle to failure in the LS7? Many have even postulated that there is no proof valve guide wear is the reason for failure due to the lack of post failure inspections.
There have been no inspections of the SS valve modification and they seem to be running fine. Does that mean they don't have the issue? Or do they have guide wear as well and just haven't failed so everything must be ok. You cant have it both ways, even though some want to on this forum.
12-21-2013, 12:02 PM
#25
Burning Brakes
Just because the car is running doesn't mean there isn't an issue. All the people who dropped a valve could say the same thing 1 mile before it happened. I know of 3-4 people locally that were running fine and would have said the same thing but when they pulled their heads they were all 3-5x out of spec. Does that mean they didn't have an issue?
12-21-2013, 12:35 PM
#26
Instructor
08 with 10,000 miles, no problems so far. Never checked but always worried about it. Completely stock down to the original tires.
Last edited by z06 driver; 12-21-2013 at 12:37 PM.
12-21-2013, 12:35 PM
#27
Just because the car is running doesn't mean there isn't an issue. All the people who dropped a valve could say the same thing 1 mile before it happened. I know of 3-4 people locally that were running fine and would have said the same thing but when they pulled their heads they were all 3-5x out of spec. Does that mean they didn't have an issue?
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.
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.
Even those which reach the end point of "valve failure", may never be confirmed to have had "out of spec valve guides", because a lot of the failed engines are not subsequently checked for guide wear. Indeed we are seeing this now.
Until that is done, and actual valve failure is shown to be consistently accompanied by guide wear, then it will be difficult to say just how much of a role guide wear has had in the broken LS7 valve failures we have seen thus far.
Consider this: There were hundreds of thousands of LS1, LS2, LS3 equipped Corvettes built.
Someone else may have, but I have not seen where very much effort has been made to evaluate guide wear in those cars.
As a result, the tendency seems to be toward a belief that it does not affect, or is not as prominent in those cars as it is in the LS7.
But again, really who has actually "checked" any significant number of those cars to determine whether or not guide wear is or isn't a frequent occurrence?
If it is, well then one would have to ask why it seems to not progress to the end point of valve failure.
If it is not, well then would have to ask; "why not?"
100% 
Especially in light of the above information by hoefi.
Last edited by '06 Quicksilver Z06; 12-21-2013 at 12:41 PM.
12-21-2013, 12:47 PM
#28
Melting Slicks
Postulated but ultimately unsubstantiated based on wear measurements recorded beyond that limit that have not failed.
Guessing and unsubstantiated evidence seems to be the norm on this forum.
We guess there the SS valve modification is fine because it has not failed yet, so it must be fine. Probably the worst offense of guessing to date.
We guess that cars with wear will all fail and that there some magical number that is the breaking point. With evidence to the contrary.
If you shoot in the dark you will eventually hit something, so I guess it could take a long time before we reach the real answers.
Guessing and unsubstantiated evidence seems to be the norm on this forum.
We guess there the SS valve modification is fine because it has not failed yet, so it must be fine. Probably the worst offense of guessing to date.
We guess that cars with wear will all fail and that there some magical number that is the breaking point. With evidence to the contrary.
If you shoot in the dark you will eventually hit something, so I guess it could take a long time before we reach the real answers.
Last edited by propain; 12-21-2013 at 12:51 PM.
12-21-2013, 12:54 PM
#30
It goes without saying that hoefi's numbers are not necessarily "golden rules" or "absolutes", and that there will inevitably be exceptions which actually ended up with outright valve failure below the point of wear which he indicates, and that there will be instances were valve failure has not yet occurred in cases where wear went beyond that which he refers to as Stage 3.
12-21-2013, 01:05 PM
#32
Melting Slicks
06 with 88,000+ miles - not inspected yet but no problems (ie failures) yet. Planning on inspecting everything when I hit 100,000 which should be sometime late next year.
12-21-2013, 01:56 PM
#35
Pro
12-21-2013, 01:58 PM
#37
Pro
