EGash

As this is my first official post in the C6Z section, I think I'll start with a very short history...

Up until last October I had owned 2 different C5's for a total of about 8 years, when I decided to upgrade to a C6. (If you want, you can see my 1st Turbo'd C5 here: http://forums.corvetteforum.com/c5-f...s-results.html)

A friend had a minor accident in his ~25K mile 06 Z06, so we worked out a trade, My 2nd (bolt ons + Nitrous) C5 and some cash for the Z, which was in need of a Fender and bumper.

Good Side:



Bad Side:




Fast forward a few months (and one very expensive CF fender) and I am the proud owner of a beautiful C6Z... now begging for a few mods.

Here's the car the day I got it back from the Bodyshop. Yes, I do know that is snow... :-0



I began gathering parts for a heads/cam swap. My plan was to install the cam package, Dyno & Track test, then install pull the heads and have them milled/ported etc..

I purchased a popular moderately large cam kit from a reputable forum vendor, a FAST 102 intake, NW 102 throttle, an Ls3 fuel rail and a set of injectors. (The car already had 1 7/8 Headers)

I took my time with the Cam install, here are a few pics from the install:















All Done:


Once the install was over, I loaded a base map and it started and idled on the first crank. So far so good, no leaks, drips, bad noises, it actually ran pretty well. I spent a few hours over the next couple days street tuning low/mid throttle, idle, and transients, etc.. After about a week I took it to the Dyno to do a few power pulls and tune WOT.



I was conservatively progressing on the tune, and the car was making over 500rwhp (I typically use a Dyno Dynamics dyno, which reads about 12-13% lower than a DynoJet, in other words this would have been in the 560-570 rwhp range on a DJ, but this pictorial isn't about dyno comparisons, so lets not worry about the dyno numbers)

What happened next was crushing...

During coast down, just above idle speed (the log later showed approximately 2000rpm) the engine made a terrible clattering noise. I shut it down immediately. We began inspecting for damage. After removing the valve covers, one of my friends and coworkers keen eye noticed one of the valve stems was not properly aligned with the rocker.

I didn't get a pic of that, but I did get a pic after pulling the rocker off.

It's a bit difficult to tell from the angle, but the valve stem is about 1/4"-1/2" higher than the rest. That's Bad.



I pulled the plug... Also Bad.



I had the car towed back to my house from the shop



After a 5 day business-ish trip to Puerto Rico (and the worst sunburn of my life) I tore it apart.



That looks a bit out of place:


That looks a LOT out of place:




That doesn't go there:




Piston Damage:




Sleeve Damage


For those of you that can't tell from the pictures or aren't familiar with the inside of an engine, that is a broken exhaust valve. When it broke it damaged the cylinder head, piston, and cylinder wall. Some broken Ex Valves have caused much more damage, there are threads on here with cracked sleeves and broken pistons. I suppose I was fortunate, the damage could have been worse, but the end result is essentially the same.

Now this happened on March 8th, and I was content not to make this post and not share this bad experience with the group. However, this thread:

http://forums.corvetteforum.com/c6-z...wn-up-yet.html

... caused me to change my mind. One comment from that thread was "I hope none of you experience what you're mocking... I have" - KLLRVET After reading that, I decided I would share my experience.

Unfortunately this happened at an unfortunate time for me financially, as I was/am in the process of buying (my first) house, so the car has sat in storage since March. I plan to rebuild it once I'm settled in the new digs (unless someone wants to buy it as it sits, which I would consider)

In conclusion:

Do I think the hollow 2 piece Ex Valves are the problem?
No; I believe premature excessive wear in the valve guide that causes the valve head not to hit the valve seat squarely; which is compounded with higher lift cams with faster ramp rates and higher pressure springs. This simply finds the weak point on the valve, just past the weld on the valve stem.

Do I think that LS7's are weak?
Not as a whole; but any mechanical system is only as strong as it's weakest component. The Ls7's have demonstrated some well documented weak points.

Do I wish I would have pulled the heads, milled/ported, and had new guides and SS valves installed at the same time as I did the cam swap? Yes; Obviously.

To those of you that have beautiful Z's that start and run, have fun with them, don't take them for granted, and go bang some gears for me.

Thanks for reading,

spra4u

Very sorry to hear that and see what happened. Although thanks for the great advise.

Mopar Jimmy

Sorry about your misfortune that sucks.

This type of stuff is why I am sticking to the old words of wisdom of
Stay stock, stay happy (except for exhaust and cai). These cars are quick enough out of the box and are pretty darn reliable when not tampered with (and nice to keep that GMPP warranty in tact).

By the way, LOVE the silver with the black wheels and best of luck on getting fixed up!

'06 Quicksilver Z06

Sorry to hear that your engine failed shortly after your cam install.

Also thanks for the pics and information.

kenw

Very good post, hope you can rebuild soon.

I could not leave my Vette broke, the house would have to go.

QUAKEJAKE

Sorry if I missed it somewhere in your thread but did you beef up the rockers and springs they are the weak link in a stock LS7?

C5 Frank

I am sure this is not the 1st post in this section you wanted to make. Sorry to hear about the broken valve and collateral damage. I suffered a broken valvespring on a 100% stock car 3 years ago. I was fortunate to shut the car down before the valve broke. Still, the car got new valve, spring, guide, lifter... ect on that cylinder. My car was down at the dealer for 24 days. I got the car back and it has run perfect since (knock wood). I still have a GMPP warranty and plan to continue to keep my car stock. There is no question these motors have a few weak points. They are still IMO one of the baddest NA motors ever produced... But the bottom line is the vast majority of LS7 have been trouble free. That says it all...
Best of luck with the repair!!

MyOwn69

BUMMER!!

Thanks for sharing your story - looks like you were meticulous in your attention to detail while working on your baby. So sorry the results were what they are.
Good luck on the rebuild.

azmusclecar

I admire your thoroughness and calmness through the whole post. Usually a poster will add a lot of expletives in their post. Your posting was rational, and very informative. I wish you the best getting both your house and your ride in order. I wish I could make some mods to my stock 07Z but like you, I'm dealing on a house and have to watch the funds. I'm sure you'll be back here posting better news in due time. Soldier on.....and sorry for your misfortune but no one was harmed.......it can all be fixed.

dsevo

Great post. Thanks for sharing.

EGash

You're welcome. Thanks for the kind words.

Yeah, it looked awesome with the Black Spyders and black full length spoiler. I had planned to black out the Halo and Roof as well... Maybe in the future."

You're welcome, thanks for the kind words. I did get to drive it for about a week with the cam installed, but sadly never over about 30% throttle and 4K rpms :-(

I'm really just buying a garage for my car... with an attached house ;-)


The Cam kit included dual springs and Ti Retainers kit. All were properly installed. You can see the springs in the pics. The Rockers on the 07's were suspect to failure, but from what I've seen that's limited to the 07's (perhaps I'm wrong) For what it's worth, I did plan to do the Comp trunion upgrade in my next round of mods when the heads were pulled.


True, my original plan was to do a similiar pictorial, but instead detailing the buildup and results form several stages of mods. The vast majority of Ls7's may be trouble free, but I did not want to be a part of the "unreported" failures group.


Thanks. I am fairly meticulous with most everything; very much so with this project.

Thanks. I'm sure I had a few choice words the night it happened, but there's no reason for me to rant and curse on a public forum months later. I'm planning to have the engine out sometime next month, pending I can close on this house in the next few weeks as planned. At least then I can stare at the engine on an engine stand while I save up the $$ to rebuild it :-) Good luck in your house dealings as well!


I case anyone is wondering, my plans include the cylinder head(s) taking a trip to WCCH for repair, possibly porting, etc, a new replacement sleeve liner for the damaged cylinder (pray the block isn't cracked behind the scared cylinder) and a set of Wiseco 12:1 pistons, along with some ARP fasteners, a Mcleod RXT clutch I have but never got to install, and if funds allow, another FAST 102 intake setup.

Landru

An excellent synopsis of events if ever there were.
While it's the pits you're having to contend with this it's also noteworthy you've the skill(s) to deal with it, yourself.
Many of us are at the mercy of a dealer wrench and dealer labor/parts rates; assuming, a warranty is no longer in-force.

Your comment essentially saying 'a chain's only as strong as its weakest link' is quite true & the bottom line IMO. IIRC the L-88s had problems with valve spring breakage resulting in valve(s) dropping into the cylinder & tearing everything apart. I had a friend with a L-88 in the day, it happened to him *twice*. The guy's folks had deep pockets so it was always properly repaired; but, had that been my car? It'd probably still be sitting on blocks to this day, 40 years later. These types of failures are expensive in the extreme most of the time.

Point of my mentioning the L-88 is Ecklers etal were advertising retaining clips that'd prevent valve(s) dropping when the uber-stiff valve spring(s) failed; hence, saving an awful lot of grief & expense.

Which now begs the question of Chevrolet: If Chevrolet went through the hassle of designing, & building such a magnificent engine as the LS-7? WTH haven't the weakness(es) of the entire valve train been addressed & improved over the now 7 year run? I understand there're afremarket components available, but what about Chevrolet's role in this matter is my question?

Damned motor's been around since '06 so there's little if any chance Chevrolet could ever be accused of acting too quickly OR not understanding what's happening. Is there.

RFZ

i feel for ya...but ...it was a modded car....i have used dual springs and titanium retainers on ls motors before with terrible results...imo behive springs are the best for an ls seriers motor....looks like you did a nice job on the install....but as soon as the mods start the maintaince and repairs go way up...as does the expense...best of luck with the repair

mirage2991

An increased spring pressure can destroy a valve as well. What was yours at?.

hiznhrz

EGash, thank you for one of the most thorough presentations of the facts, as you experienced them, that has been posted on this or any forum concerning a potential latent defect in the LS7. I would also like to thank you for your conclusions, and recommendations.

You have objectively amplified several good points, a few that resonate with me.
1) Any mechanical system is only as strong as it's weakest component
2) Ls7's have demonstrated some well documented weak points

I would tend to agree that your particular problem was "compounded by a higher lift cams with faster ramp rates and higher pressure springs causing premature excessive wear in the valve guide" resulting in "the valve head not to hit the valve seat squarely".

I have a stock Z06 and I'm fortunate to be very satisfied with the car as it sits. It is also still under warranty. I believe the LS7 is the product of some very talented and creative engineers constrained by a few cost tradeoffs to protect the end products bottom line. In other words, it does have a few cost savings induced weaknesses. My plan has been to accumulate information while I enjoy the car until the the day it is no longer covered under warranty when I would then make a few internal changes to address weak links. At this time, the valve train is my only concern.

The objectivity in which you presented the facts of your misfortune makes your opinion valuable. I would also appreciate your opinion in a few other areas. In your mind, was the root cause "the valve head not to hit the valve seat squarely".

Do you believe your mods accelerated a failure that would have happened on a stock engine as the mileage increased on stock valve guides experiencing wear with mileage? In other words, the valve guides wear with mileage will result in "the valve head not to hit the valve seat squarely".

Do you believe it was the premature excessive wear in the valve guide (or the higher lift of your chosen cam) that exposed the "weak point on the valve, just past the weld on the valve stem" or both?

Thanks again for your objectivity and information.

AirBusPilot

I've long suspected that a worn valve guide is the root to the broken 2 piece exhaust valve.

However, it's really not that common.

Which leads me to believe it's a machining issue when the head is completed. I suspect the valve guide isn't quite square in some heads, which causes the excessive wear, followed by the valve failing because the valve head is bent back and forth over time and eventually breaks at the weld.

2k Cobra

As long as any repairs on mine will be done under factory and extended warranty, mine will stay factory stock. If I still have the car after the warranties run out, things will change.

Very good post EGash.

EGash

Yes, I do (most) all of my own work, though I will have to take the block to a machine shop to replace the cylinder sleeve/liner for this repair. I haven't decided if I will reassemble the short block myself, I'll decide when the time comes.

I don't blame GM for this. The engineers were designing a system with a specific set of design parameters. Most of the failures, including mine, were on engines that had been modified outside of that original set of design parameters. GM nor the engineers can be held to blame for a failure on a modified system that is out of their warranty period.

This doesn't change the fact that there are clearly defects/inadequacies in the valve-train on the Ls7's.

I've used Dual Spring kits on many projects in the past, on both Ls motors as well as imports with zero spring failures to date. I don't specifically blame the springs, they did their job (too well ;-) )

However I do agree that modifications can and often do increase maintenance and repair related costs. I've had several modified cars, and I've broken a lot of parts over the years, but nothing as expensive as this Ls7.


That's a good question. I did not measure spring pressure. The springs used were Patriot .650" Extreme Dual's that were included in the cam kit. Perhaps someone else on here knows the typical installed pressure on these springs on an Ls7?


Some have argued on here that the wear on the guides is due to the hollow valves transferring more heat into the guides, causing excessively hot guides, coking the oil on the guides, and causing a lack of proper lubrication inside the valve guide bore. I don't have any actual proof of this. Perhaps after the heads are inspected and repaired by WCCH we may have more information.

GMuffley

A moment of silence, please.

EGash

Thanks. I'm glad you (and others) appreciate my post.

I agree. But this is no different to (most) any other manufactured product; designed to meet a parameter set, with a minimum quality specification, and at a specified minimum cost.

The valve train is not the C6Z's only weakness, but it's probably the most expensive to repair upon failure. Your concern here is valid; which is exactly why I created this thread.

See my post above with regards to oil coking on the valve guide bore. This is a possible root cause, but I cannot confirm.


I believe the mods accelerated the failure. I also believe that if the root cause of the failure was excessive valve guide wear caused by lack of lubrication as mentioned above, or improper machining, (or any other root cause) then the failure would have indeed eventually occurred. I do seem to remember reading at least one post where this happened on a stock engine, though I don't have the thread link handy.

Yes, and I do believe the modifications accelerated the failure. But I'm not blaming anyone (but myself) for this. It's my car, my decision to mod, my labor, my tuning, and now my broken Ls7 to rebuild. (actually I did have some assistance with the both the labor and tuning from a few good friends, but obviously I'm not placing blame on them either)

You're welcome. Thanks for your post.