Crossofiron

Very aware of all the questions about the value guide issue with the LS7.

I have 23,000 trouble free miles on a stock 2011 LS7. Very little valve noise at about 1,700 rpm. Been like that since the day I brought it home brand new.

Started the car today and notice a loud ticking noise and when i started to accelerate, there was a slight surge. and stumble.Turned the car around and right back into garage. Does this seem like the dreaded value guide issue? Would driving it cause a rod through the block?

C6Z06Silverbullet

Sure sounds like it. Don't even try and start it. Pull the valve covers and see whst's going on.
Good luck!

blackvetterzo6

Dirty Howie

Agree. Don't drive. In for the results ........


DH

Dan_the_C5_Man

It could be anything .. Spark plug wire popped off, broken valve spring, etc.

But I'm confused - you say "..well aware of the valve guide issues..", but you didn't mention, at 20K plus miles, that you've pulled a valve cover to check anything.

Learn from this guy.. https://www.corvetteforum.com/forums...alve-list.html

Don't be a statistic. Pretending "that stuff happens to other people" won't get you very far.

73DBG

Too-Fast

Original owner of a "trouble free" stock Z07 with 3000 miles on it in March/April of this year, checked the heads and had bad guides. AHP replacement heads via a GMPP warranty.

cv67

If its loud and stumbling you could already have had a failure I wouldnt even start it. You can pull plugs and stick a borescope in ea cyl if youre curious..
The whole head issue...what a black eye for GM.

black00ta

It's never worth the risk, not with the replacement cost of this engine. Get it checked out and report back!

Les

It could also be a cam lobe starting to go. That's not exactly uncommon. I've had that happen in addition to two head replacements due to excessive valve guide wear. If you find guide wear and have the heads gone through, be sure to have the cam looked over while things are opened up. Good luck.

Landru

No excuse, really.
LS7 owners have an obligation to inform themselves w/ this motor.
IF they don't when this well known issue occurs it's on them, sorry to say.
Can't un-ring the bell, now.

Could be anything as others have stated; however, guessing if a catastrophic failure re valve(s)?
It'd have seized-up right then & there w/ oil/coolant everywhere underneath via hole in block.

Do NOT attempt starting & get it inspected post haste, might've got lucky if only a spring etc.

Crossofiron

Thanks for all the advice. I had hoped that I would not get screwed from a discussion with the Bowling Green Plant Manager at a Corvette Corral function at a ALMS race at Laguna Seca about 5 years ago where he told me that the "bad heads" did not affect the 2011 year. Same thing that I heard from a variety of other so called experts. from the dealership to some folks here on the Forum.

I will know what the real issue is after I get it torn down by American Heritage. Lucky for me they are only 45 miles away!

G8Pumpkin

I have a 2011 and about 27,000 miles just in the process of doing the heads there where a bunch of guides out of spec. Cam was also just starting to go so new cam as well. Sent my intake valves back to Del West to have them super finished which is a no charge item by the way all where good so did not need to buy any new intakes. Replaced exhausts with Ferrera hollow stem exhausts. Cam is crap surface hardening just starting to go and its not straight so have replaced that with a Cam Motion with there highest quality core material, also from what I have seen in mine the cam goes first then takes out the lifters then you lose the motor some feel the lifters go first but its hard to diagnose an engine post mortem that has had major destruction, in my case I was lucky to be able to witness first hand the cam was going first most lifters where still good but have replaced them with much better Johnson slow leak down ones. Also the cam chain had so much stretch in it check yours carefully. Should have the heads back from the machine shop next week so I can finish reassembly. Highly recommend you put in better pushrods the stock GM ones are junk I have some that are .032 out of column, also do some kind of rocker bearing upgrade.

OneMeanZ

I'm going to be pulling the heads soon and my 39k mile Z06, whats the best way to check the cam? Pull the lifters and look for scoring?

Undy

He's just regurgitating GM's official lie. Being a GM employee he has to repeat the falsehood … or join the ranks of the unemployed.

G8Pumpkin

Yes just take out the lifters and look at the cam carefully if there is any sign of the case hardening starting to wear replace the cam. At this point also change the timing chain I used the c5r race chain if I had to do it again would look into a Cloyes double roller but do not know if there are clearance issues somebody will know what fits that is better than stock as it is obviously not good enough judging by the slop in mine so there was no hope of it giving accurate cam timing. The cam can be removed without taking the engine out but it still is a lot of work. Search ytube for videos, the steering rack does not have to be completely removed from the car, slide it over to the passenger side far enough to get clearance. Also if you are this far into it I replace the crank damper with a middle of the road Power Bond unit or you can go all out for an ATI one, when I inspected mine carefully on the back side the rubber was starting to crack the old damper still ran true but when you have put this much effort into getting this far another few hundred is well spent as I wouldnt want to tear it apart again. I spent a lot of time with an air hose cleaning from the back side the air conditioning condenser as there was lots of crap in it which also impedes air flow to the rad as it sits in front of the rad.

BRISLS1

You guys stop the car and send it to the shop for making a sewing machine sound? If I did that, my car would have the same 180 miles on it that it came with. My car has never had a quiet valve train.

Off topic, can I get a refresher on the mechanics of dropped valve? If it slips off the rocker, shouldn't the spring keep it out of the cylinder permanently? The valve enters the head against its will, right?

Thanks

BigVette427

That's the best of both worlds in the LS7 community, at least. My aftermarket warranty would not help me out with my heads. Getting your heads fixed the right way at AHP and having a warranty pick up the tab. Most warranties won't cover you unless you have first experienced a failure, which at that point, is more than the warranty I had would even cover. Always helps if you have a top notch and experienced LS7 shop to help you out, as AHP is and does.

I really don't think GM has a conscience, they are not ashamed of anything.

I saw it on more than one occasion on this forum before I did my heads, and that was the main reason I decided to do a cam swap while I had my heads out. Even if it were comparable specs, only to just get a higher quality camshaft (and better lifters.)

The 8620 carburized nickel-chromium-Molybdenum core camshaft used to be something you'd only see in a top fuel dragster or something, but in the LS7 for $50 more, the peace of mind is well worth it. Johnson 2110 SLR lifters are well worth the extra coin as well, considering that you have to remove the cylinder heads to swap lifters in LS motors.

I don't think you would have any issue with the C5-R timing chain assuming it's a genuine Katech chain. That chain is still used on tthe C7-R.

I agree on the balancer. As long as you already have it out, given the bad reputation for bad balancers in LS motors, I couldn't in good conscience put the OE one back on. The PowerBond Race Series balancer for the LS7 I would argue has a better reputation for durability than the ATI LS7 variant; there has been too many ATI LS7 failures on this forum. I'm sure ATI has whatever was wrong corrected by now, but I wouldn't spend more for the ATI balancer when the PB Race Series LS7 balancer (PB1503SS) is less expensive and a very high-quality part. (And it doesn't have to be re-built over time, which on a Corvette is a big deal given it's not easy swapping the balancer on these cars.)

Crossofiron

Value train always had a bit of clatter at 1700 rpms. That is normal. This time the sound was very different and and the car stumbled leaving driveway. Also way different. Something is wrong and rather than throw a rod and have to spend $14,000, worth it to me to have it towed to American Heritage.

Stay tuned as I will post the findings. Damn.

BigVette427

The problem is when the head of the valve breaks off the stem and hits the piston, and subsequently proceeds to blow a hold in your engine block. See the attached write up by Jason at Katech.