Broken Intake Valve from Valve Float 6.2L L92?

[t69chevelle]

Hi, has anyone else had this same problem, mine is an 07 Denali 6.2L and has 94000km on it. We were just getting up to speed on the highway and there was a loud ticking noise and a drop in power, then the computer started shutting stuff down and it died, I got it going and made it my friends shop, barely. So there was a P0305 Misfire Cyl #5, so after some diagnosing we finally found that the Intake Valve on #5 Cyl had broken off just below the Keepers. Luckily the Valve did not drop down and get caught but it was bouncing Up & Down(my ticking noise) and marked the Piston but it could have been catastrophic if the Valve had of exited the head or went through the Piston.
So we removed the Driver Side Head and took it to my Local Machine Shop and after tearing it down I was told that all of the Valve Seats had been pounded from Valve Float. So I just removed the Passenger Side Head and I am having all New GM Valves(I guess there are no aftermarket Valves for my L92) and we talked about doing a Spring Change but after finding out that the only Springs we could find were $700.00can(they are not Beehives but a traditional Double Spring) we decided to Shim the Factory Springs to get a little bit extra pressure out of them.
Has anyone out there had anything similar happen? My Denali has had very little added to it, a K&N Cold Air, Throttle Body Spacer and a Bully Dog Tuner(set on the 87 Octane setting). It has just over 94000km on it and I run MSD Wires and NGK Iridium Plugs. My problem here is that other then the odd hard run on the highway I drive it like I own it, I am very disappointed with my 6.2L at this point, I love the power but it should not be having these problems with so few KMs on it. Also my Denali does not have the Active Engine Management or the VVT, I have been told that an 07 should have the 4cyl shutoff but mine does not. Any one out there with any knowledge or anyone that knows of an ongoing problem let me know, Todd.

 

[Jason_S]

Sounds like you over revved your engine.

Will you be pulling the passenger head for inspection also? I suggest checking all valves for straightness also.

If all valves show the same type of damage, I would believe the cause to be a driver that thinks that he/she Dale jr. or Burt Reynolds as the Bandit. If only one head or a few valves show that kind of damage I would suspect a material failure or quality issue.

 

[t69chevelle]

Thanks but it has never been over 5500prm, my Bully Dog has a Rev Limiter in it also. I do not over drive my Truck but a Truck with this power should be able to handle a bit of hard use, we are wondering(my engine builder) if it is the added weight of Vehicle as opposed to this motor in a Camaro or Vette. At over 5000lbs it is very heavy but still for a Top of the Line Truck it should last longer than this.
My reason for posting this thread was to find out if anyone else has had a similar issue, I know that you can install any # of Superchargers and I think there is even a Twin Turbo kit for these and most do not need to have the engine touched other then the Tune. thanks.

 

[Jason_S]

I am not aware of this being a common problem with this engine/vehicle combo. Most people would never notice valve float until they are in a situation similar to yours, and on a Denali they tend to just replace the engine and carry on with out much more thought.

Also, in '07 the Denali was not offered with AFM. There could be an issue with the VVT, but it doesn't seem common either.

I missed the part where you pulled both heads. Did all 16 valve seats show the same signs of valve float? Do all of your springs still spec out to similar numbers? Stiffness (I forget the proper term) and length? How was your oil pressure?

A hollow valve (such as those found stock on an LS3) could help by reducing the amount weight that the spring has to control, but those have their own risk and tend to respond even worse to valve float.

Just because a vehicle is at the top of that particular product line, does not mean that all of the components in that vehicle will also fit that description. The targeted demographics for the Denali wont typically understand, appreciate or know to demand that level of performance or quality in the driveline components, so GM doesn't offer it. A Camaro or 'Vette are a different story.

 

[Speck]

Thanks but it has never been over 5500prm, my Bully Dog has a Rev Limiter in it also. I do not over drive my Truck but a Truck with this power should be able to handle a bit of hard use, we are wondering(my engine builder) if it is the added weight of Vehicle as opposed to this motor in a Camaro or Vette. At over 5000lbs it is very heavy but still for a Top of the Line Truck it should last longer than this.
My reason for posting this thread was to find out if anyone else has had a similar issue, I know that you can install any # of Superchargers and I think there is even a Twin Turbo kit for these and most do not need to have the engine touched other then the Tune. thanks.

Yes, a few years ago I too had a similar problem. I only had around 60k miles on mine and started to hear a very loud tick and reduction in power. I had taken mine to the dealership since it was still under warranty, and they found the valves had marks on them along with a problem with enough oil circulating and lifters showing wear. They wound up replacing the heads on my 6.2, but never really explained all of the problem. I still have a very loud ticking sound, but is now only on a cold start and during warm up. I do not drive mine too hard as well with the exception of the occasional romp getting on the freeway.

Best of luck, don't give up on these motors yet, as the 6.2 is truly a great engine.

Joe

 

[Dank Denali]

Yes, a few years ago I too had a similar problem. I only had around 60k miles on mine and started to hear a very loud tick and reduction in power. I had taken mine to the dealership since it was still under warranty, and they found the valves had marks on them along with a problem with enough oil circulating and lifters showing wear. They wound up replacing the heads on my 6.2, but never really explained all of the problem. I still have a very loud ticking sound, but is now only on a cold start and during warm up. I do not drive mine too hard as well with the exception of the occasional romp getting on the freeway.

Best of luck, don't give up on these motors yet, as the 6.2 is truly a great engine.

Joe

Can you describe the loss in power you had? My 2013 Denali just started having similar symptoms today but the power loss is kind of hard to describe. Its almost like the engine/transmission gets stuck for a couple seconds, especially in 2nd. Going to try to take it to the dealer tomorrow....super pissed, barely had it 2 months!

 

[t69chevelle]

As far as the Power Loss it was substantial, I was just getting up to speed on the Highway and it was an instant loss. There was also a very pronounced ticking noise, the only way I could keep it running was to keep the RPMs up. It would not idle at all, after we figured out that it was intake valve it made sense because the valve was not sealing so that compressed air & fuel were going back up into the intake. Your problem sounds to me like at transmission fault, if it is hanging in gear before the gear change that sounds like the Transmission or something to so with the speed sensor. I have years of experience with older cars so when it comes to the electronic side of this stuff it really is a Dealer job or someone you trust but your is still under warranty so the dealer it is.
Good luck and hopefully it is something that is easily fixed. Todd.

 

[Dank Denali]

Ya I was thinking transmission too until I realized the very loud ticking is coming from the engine...but maybe it's both

 

[t69chevelle]

You hadn't mentioned a ticking, usually a ticking noise is valve train related. Not always but that is my experience with broken valve springs and bent pushrods(not in my truck). Let me know how you make out, that is why I wrote this thread was to just see if anyone else had a similar problem. I talked to a guy with a 2011 Denali and he had the Gear in the Front Diff break, just something else to worry about. I was not too happy when my Engine broke either because it had pretty low mileage on it, you just never know? Todd.

 

[Speck]

Can you describe the loss in power you had? My 2013 Denali just started having similar symptoms today but the power loss is kind of hard to describe. Its almost like the engine/transmission gets stuck for a couple seconds, especially in 2nd. Going to try to take it to the dealer tomorrow....super pissed, barely had it 2 months!

Similar to how @t69chevelle described his incident, mine was pretty significant in the power drop. It felt completely anemic when trying to accelerate and also had a very hard time idling. Unfortunately mine occured long enough ago that I'm having a hard time remembering all that was going on with it. It did occur around the 60k mile mark and I'm currently at 109k and haven't had an issue with the engine since. Now, I just wish I wasn't having issues with the rest of the truck...

Joe