Newbie with LS7 Questions
 

Hello All,

After 30+ years owning various Porsches, a stint with a Mustang Mach 1 and currently a 2007 Mustang Shelby GT I decided to join the Corvette Nation.

After a bit of research, I've narrowed down my target car as a 2007~2010 ZO6 on blue.

I've been reading in the forum about valve issues with the cars. Is the issue just affect the LS7 or the LS2 and LS3, too. Is the fix just a valve job?

I did a search but was flooded with info and got more confused.

Thanks in advance for any help.

John

It's with all LS7 motors only....
Doesn't matter what year, they all have valve issues.

:iagree: potentional issues. opinions vary but I would have a valve job by a trusted shop! PERIOD! :thumbs:

Thanks, guys.

It seems no matter what brand, there always is some design issue that made it through QC and now the customers have to fix it.

Porsche recently had an intermediate shaft bearing seal that the customers had to fix.

Is this something the dealer can do?

And what exactly is the issue with the valves? Valve guide concentricity?

The short answer is valve guide concentricity being off (valve seat run-out) due to machining errors by Linamar, the bastards that machined and assembled the LS7 heads. Valve wiggles (side loading), guide wears, valve overheats and snaps. And the party ends. There is a much longer answer, but it has literally been re-hashed, examined and explained no less than a few thousand times here. There is still to this day a pending lawsuit against GM for this exact issue. If you need to know the hairy details on our heads, they are all here for you to read. I do realize it is almost too much, and overwhelming.

Most dealers can't fix it, because they either don't know about the problem, don't understand the problem, don't know how to determine if there is a problem and/or don't know how to fix the problem. There are also a few users here that are in denial, so I would suggest you ignore them if they chime in as they have no clue what they are talking about.

You need to do a wiggle test first. This will give you an idea, but is not entirely accurate. If the valves wiggle, there could be a problem. Next step is to pull the heads off. If you want to know if they are out of spec, then you need to measure the valve stem to guide clearance. The maximum clearance allowed is .0037 in. Anything greater than that, or approaching that after multiple tests over a period of time is out of spec and has a larger probability of causing a catastrophic failure (BOOM to your motor).

The fix is to replace the guides, examine the valves and other components and replace as necessary. The entire valve train should be inspected in fact. A dealer will replace with another set of factory heads if under warranty and read out of spec (usually), leaving you with the same problem you started with. So no good with them.

So what you need to do is remove the heads (or pay someone to do it if you can't), and then send them to a company like American Heritage Performance, WCCH, AI etc. They will "fix" the heads for a fee ($1200-$2000 depending on what you have done) and send you back the repaired heads. These guys know what they are doing, understand the problem and will correct it. They ship them back to you and then you reinstall the heads. You conceivably could pay a dealer to do the labor, but I wouldn't. There is a guy that posted here recently that had the dealer doing his work for him (replacing heads he had fixed by AHP) and they (dealer) forgot to install the lash caps on the intake valves and the motor almost blew up. He is still dealing with it last I knew and who knows what damage occurred. This could happen at any shop, but is more likely at a dealer that doesn't understand what is going on.

I do my own work, as do many here, so my heads come off once a year for inspection and refreshing. If you can't do your own work, then you need to find a reputable shop that understands how to work on LS engines and in particular understands the problem we face with the LS7 heads. So you must do research, ask questions and be careful. Or start turning a wrench.

LS7 Valve Guides
 

I can appreciate you being flooded and confused.

I vascilated back and forth 4 winters as to tear my LS7 down and have the valves replaced.

Honestly, if you buy a Z06 with an LS7....... please, please, please have the valves/guides replaced you will sleep much better and you will LOVE the Z06!!!

Very good and to the point answer. I agree completely. Please do not wait, have them pulled, checked and fixed.

:iagree: excellent, succinct summary by Mordeth

Thanks again for the detailed information.

I am a mechanical engineer, but brand new to Corvettes

Just so I understand, the center axis of the valve seat isn't concentric with the center axis of the valve. So, normally, when the valve closes it nests into the valve seat where the surfaces all align and mate. Since the valve seat was installed off axis or skewed, the valve tries to nest with the seat, but has to move off axis to do so. That introduces the side load you mentioned which increases the valve guide wear.

Does that rambling make sense? Or, am I totally out to lunch.:crazy2:

Thanks again for the info.

Is there any relationship to miles with the engine failing? Like usually around 60k or so? Or can it happen anytime?

Also, did GM cover the blown engines that happened while the car was still under their powertrain warranty? Or did they just replace bad with new bad heads?

Your understanding of the concentric offset is dead-on. There is no rhyme or reason for when a valve may fail. I've only been a C6Z owner for a few months, but even in that short time I've read here about valves breaking with just a few thousand miles on them. Conversely, my motor has 70K miles on it, bone stock, and nothing has broken, but I'm having the guides done (and other work) in a few weeks.

Outside of this forum, hardly any human being knows of a "valve issue." It affected less than 1% of the LS7's, and almost all of those motors were modded.
The LS7 is as solid as any of the other LS motors. I have owned everyone, and am currently on the LS9. I left my Z06 stock and drove it for 45K miles, tracked it hard 4-5 times a year and it was a beast.
If you mod the car, have them checked. If you are leaving the car stock, drive the hell out of it. If every Z06 owner red these threads no one would ever even buy one. Sheesh.

Oh. Okay. Good to know.

I was having second thoughts on getting an LS7. I was under the impression that the problem was widespread.

Thanks for a reality check.

Wrong, no, bad advise, don't listen... How many more ways can we say this, over and over again?

DON'T BUY A CAR WITH AN LS7 UNLESS YOU CHECK THE VALVE GUIDES, PERIOD - END.

That is all, sheesh.. :cheers:

Jaydubgt, you are fooling yourself if you buy a car with the LS7 engine and ignore the valvetrain matter.
A proper inspection/measurement is needed to determine if the engine you own is either "in spec" or "out of spec."
All model years are potentially affected.

The LS9 is also similarly affected, albeit likely to a lesser degree.

OK. I got the message. Thanks!!

I wasn't going to buy a Z06 without the valve issue discussed, but you've convinced me that I must go further then just discussing it.

Can the dealer inspect/measure the valve/valve guide play? I know there's no confidence that they can fix the situation.

Thanks again for helping me miss stepping on a land mine!!:cheers:

The only approved method to test valve guides requires disassembling the top half of the engine, disassembling each head, and measuring the ID of the guide at multiple points. It's a very expensive endeavor. If people are going to go that far, they usually just put freshly machined heads back on.

There is another test that GM _used_ to use with the heads still on the car. It's called the "wiggle test" and someone will likely recommend it to you. The wiggle test isn't accurate enough to determine if you're marginally out of spec, but it _could_ indicate if it's grossly out of spec. GM has said that the wiggle test can falsely indicate worse guide wear than what actually exists.

The most sound advice, in my opinion, is simply to remove the heads and proactively "repair" or replace them. I chose to replace them with aftermarket castings and would do so again. GL

If you know they can't fix the issue...why have them check for you? I know that's a general question on your part and answer on mine. Find a shop that works on LS motors for a living. At least find one that does valve jobs for a living and you should be fine.

And as I always recommend. Put the "area" you live in on your profile. I don't live in Dayton but it's within driving distance. It makes it so much easier to recommend local shops, etc. There are also shops that you can mail your head to and they will perform the work and return them to you.

As you stated earlier...there is something wrong with every car! The autos have issues as well. Not maybe 1300.00 in cost but still an issue. Don't let it scare you off. I love the 427.

Wrong, wrong, then some more wrong.

:iagree: