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Discussion Starter · #1 · (Edited)
Bent Pushrod, Loose Rocker, Broken Valve Spring, Toasted Intake Manifold

Well at 26030miles my 2016 JG M6 had her first real problem besides a single steering rack failure prior to the recall.

Yesterday morning, cruising to work on the highway in 6th gear at about 1750-1800rpm and around 72mph my Center Display switched to "Service Stabilitrak", TCS light came on, and eventually MIL started flashing intermittently. It immediately felt like a flat, but the TPS and handling suggested otherwise. I realized the feeling of a flat was actually the engine running lumpy, and with a sluggish throttle I put it together that it was a bad misfire....great.

Like a numb-nuts I continued to drive my tractor sounding car cautiously the remaining 8.2 mostly highway miles to work while my brain processed what was going on. Stupidly my brain didn't tell me to pull over and shut the engine off. I did however have the foresight to park in a spot where I knew a flatbed could get to...so that was something. I checked the codes, and double checked with ONSTAR - P0106 for a MAP Issue, and P0300 for missfiring. Of course they told me it'd be fine to drive to the nearest service center.....eh NO!

I'd just filled up 17miles before the missfire started so was hopeful it was a bad batch of fuel, or a shot injector, or a bad MAP sensor from the oiled OTR filter.

I got a Chevy provided flatbed tow to my preferred Service Center (stupidly drove it onto and off the flatbed - very sluggish starting), and then they drove it around to a service bay.

Unfortunately for me I bit the warranty when I installed a different tune to hopefully take better advantage of my OTR intake. I then later switched the tune back to the original as I preferred that to the supposed 'custom' remote tune I'd installed. So I'm not going to bitch and moan about loosing the power train warranty. I'll man up, pay up, and not argue.

I drive like a nanny. Have hit the rev limiter about 3-4 times in it's life. Have never had a mismatched downshift or mechanical over rev, have never done a burnout or tried for a best 1/8th or 1/4 mile time. I did have a high pitched squealing sound start around 10K miles when between 4000-4500rpm. The squeal sounded like it came from the drivers side of the engine bay. The dealer never was able to find the source of the sound, but it went away around 20K miles, and I was rarely above 4000rpm to listen for it. Oil and filter have been changed every 3000miles with Mobil 1, and serviced on schedule. No other mods.

The dealer service techs confirmed today via the service advisor that Cylinder 8 has the following issues:


-Exhaust rocker arm loose, but bolt was tight,
-Pushrod was bent,
-Valve spring was broken. :(
-No 8 intake runner on Intake Manifold melted/failed (P0171, P0174 Lean Bank 1 and 2 Codes - codes were after valve spring and pushrod replacement and on post assembly test drive by mechanic. Mechanic did not check integrity of intake manifold when the manifold was removed to pull the head.)


They haven't performed a leak down test, nor scoped the cylinder yet or done additional diagnostics until I gave them the okay. They're talking about pulling the head. I probably won't know more on the damage till Monday.

Okay so the main concerns are damage to the piston, cylinder walls, exhaust valve, and camshaft lobes right?

Should there be any concern of additional damage from circulating crud if the camshaft is worn?

Another question I have, and my main pondering is how could this happen?!?

Could a broken exhaust valve spring alone result in a loose rocker, and bent push rod?
Or is it more likely the bearing in the rocker was toast, and the increased play resulted in the spring breaking and rod bending?

Correct me here if I'm wrong - but on these engines a tune can only effect the timing and duration of both fuel injection and spark right?

So ultimately how rich or lean, cold or hot the combustion is in that cylinder which would burn or otherwise damage the piston, valve faces, or cylinder walls. I wouldn't think a tune alone (bad or good) would result in this damage?

So thoughts please on how to handle the repairs, and make sure the service techs do the job right the first time and catch everything. I don't want to end up with additional surprises down the road, but also don't want to have to deal with a complete engine teardown or in the extreme buying a new LS3.
 

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well that really sucks, if the cam is worn then all bearings and rings are suspect IMO. A loose rocker should result in valve not fully opening which should not cause the spring or pushrod to break unless the rocker somehow locked up with valve open, the piston hit the valve, bending the pushrod, and breaking the spring. I would suggest have the intake pulled and cam checked 1st, if damage to the cam, motor needs a rebuild. If cam is good, pull heads to check piston tops & cylinder walls for damage.


Time for a LS7 ?
 

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Don't let them put stock valve springs back in. There are much better aftermarket options.
 

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The new fiber optic tv tools can look inside the cylinder through the spark plug hole, and tell you whether the piston or cylinder wall is damaged or the valve is bent. The dealership should have one of these. If the rocker is "loose" but the bolt is tight, that means the needle bearings have escaped. That mostly just makes noise, so long as the loose needles stayed out of the oil pump. If the needle bearings are not near the rocker arm, this means that the bearing failure happened some time ago. Probably the spring broke first. I have had a valve spring break on a Chevrolet ZZ3 Crate Performance engine within 12,000 miles, but I was close to home and got away with just new valve springs. To avoid this happening, the LS3 needs better valve springs, stronger push rods and different rocker arm trunnion bearings.
 

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Discussion Starter · #6 ·
So I’ve spoken to the Service Adviser twice today and asked if they’ve borescoped the engine yet. Each time he says the mechanic is planning to pull the head and will have a full list of what is damaged and needs replacing. I have no real problem with pulling the head, but it just makes extra work for them, and more cost for me. Their quote for the work was reasonable though so I guess I will just wait for Monday and hope for the best....whatever that might be.
I would be amazed if the piston and valve didn’t come in contact as others have surmised....
 

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Hmmmmm.....my "guess" on cascading failure

1. valve spring breaks

2. valve hits piston

3. pushrod bends due to piston contact "slamming" valve stem back through rocker

4. other collateral damage TBD
Seems like a scary prospect. I have searched SS forums and corvette forums and haven't found any consistent suggestion on how often to check/replace stock valve springs. I have seen plenty that suggest upgrading ( and to upgrade the cam ) -- but without any suggestion that this is an epidemic or common issue( probably millions of springs out there ), is there any suggested interval? Most common time frame is 20-25k miles, but this seems a bit low for stock cam and valve springs, don't you think?
 

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Sorry to see this happened to you

Welcome to the GROWING club of broken valve spring victims. My valve spring gave up shortly after rolling over 36k. Fortunately, I didn’t drop a valve (which is extreeeeeeeeeemely lucky).

I whole heartily agree with the post above about NOT putting OE springs back in. BTR dual springs are a great aftermarket option.
 
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It would be my guess you did not drop a valve and probably didn't have any valve to piston contact. I'm opining that your valve spring broke and then bound up on the next valve action, which bent the push rod. Everything else is most likely OK and a bore scope inspection should confirm that. I really hope that's all that's wrong with it and the cost to fix it will be very minimal. Good luck with it.
 

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Discussion Starter · #10 ·
It would be my guess you did not drop a valve and probably didn't have any valve to piston contact. I'm opining that your valve spring broke and then bound up on the next valve action, which bent the push rod. Everything else is most likely OK and a bore scope inspection should confirm that. I really hope that's all that's wrong with it and the cost to fix it will be very minimal. Good luck with it.

This is most certainly what I'm hoping they find. I don't know why they haven't already bore scoped it though, and instead want to pull the head.
Maybe they're being overly cautious?!?! I really should have pushed the service advisor on an answer to this. And pushed harder for them to provide photos of the rocker and spring while installed in the head once they pulled the cover off.

Fingers crossed for my Monday updates from the service guys.
 

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Been there, done that, three times to be exactly. Twice with a Coyote 5.0L and once with the LS3. Changing fuel maps have multiple effects on your engine besides adjusting simply spark and fuel. All those changes could have caused a situation where the engine went lean, causing detonation, leading to dropping a valve or getting so hot that your piston ring gap closed. All signs lead to a boom inside the engine that is going to come out of your pocket.

Your best bet at this point is pulling the heads off and inspecting the block for damage. Most likely you will have to hone the cylinder walls and replace everything related to #8. I had a similar situation and just took the opportunity to drop in a replacement forged rotating assembly from your favorite speed shop. Good luck with your efforts, I went lower compression for a safer boosted motor.
 

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This is most certainly what I'm hoping they find. I don't know why they haven't already bore scoped it though, and instead want to pull the head.
Maybe they're being overly cautious?!?! I really should have pushed the service advisor on an answer to this. And pushed harder for them to provide photos of the rocker and spring while installed in the head once they pulled the cover off.

Fingers crossed for my Monday updates from the service guys.
Well IIRC the head has to come off anyway to get the lifter out. Saying that cause I don't think I would trust it, with the bent push rod it probably got hammered on.

I think I would ask for a new lifter, push rod, rocker and spring. I doubt they will want to put aftermarket springs on it. You could always just do that later when they are done.

Man I hope you don't have a bent valve or worse. Good luck!

I guess new springs and rockers should be on my list for when warranty is up.
 

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Discussion Starter · #13 ·
Well hoping that a leaned out condition wasn’t the case. I don’t know any of the details of the tune, but it felt like it lacked some pep and always seemed to be running rich whenever I looked at it via Dash Command. So I switched back to the original factory tune as it just drive better. Maybe that with the increased airflow of an OTR could lead to a lean condition...bit lean enough to detonate? Hmmm hope not!
 

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Matell, very sorry to hear about your issue. Have you received an update from the dealer yet??
 

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Well IIRC the head has to come off anyway to get the lifter out. Saying that cause I don't think I would trust it, with the bent push rod it probably got hammered on.



I think I would ask for a new lifter, push rod, rocker and spring. I doubt they will want to put aftermarket springs on it. You could always just do that later when they are done.



Man I hope you don't have a bent valve or worse. Good luck!



I guess new springs and rockers should be on my list for when warranty is up.


When I bent my valve, I replaced everything on the head...however, I did not replace the lifter because it seemed fine. Needless to say that it wasn’t and it broke. Thankfully the pushrod kept the pieces within the lifter body and I dodged a bullet.

Yeah, get a new rocker. I got a set of Morels - they’re like 135 bux or something- I forget now
 
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Well hoping that a leaned out condition wasn’t the case. I don’t know any of the details of the tune, but it felt like it lacked some pep and always seemed to be running rich whenever I looked at it via Dash Command. So I switched back to the original factory tune as it just drive better. Maybe that with the increased airflow of an OTR could lead to a lean condition...bit lean enough to detonate? Hmmm hope not!
No, to have a stock tune with an intake won't provide enough air flow to be outside of the ECM's learning range. Your OTR didn't cause a lean condition that resulted in this failure.

I always blame stock rockers first, since it's so well documented that the stock needle bearing trunnion arrangement is problematic. Before I read the responses, I was guessing rocker lost the needles, which resulted in a loose rocker. Loose rocker over miles caused a bent pushrod and for the spring to break due to uneven load. After reading, though, I would believe a lot of the other responses if those were provided as explanation.

In my opinion, with no warranty, you're best bet is to replace the broken components accessible without removing the head. This means not replacing the lifter, and it's a bit of a gamble. I'd only be willing to take that gamble as you don't have warranty coverage. The way I see it, if you remove the head and find a bad lifter, you'll end up replacing everything on the bottom end (or at least taking it all apart). At that point, you may as well have ran it until failure. Failure could be 50k miles, 5k miles, 500k miles...
 

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Discussion Starter · #17 ·
Okay update time.

Looks like it may have been the No.8 Cylinder intake valve spring that broke, not the exhaust....which makes it more in keeping with most of the other spring stories I've read about.

The spring looks to have broken up high, then the coils bound and held the valve rigid so on the next intake stroke the cam+lifter shoved the pushrod into a not-rocking rocker, and bent the rod.

They haven't told me of any other damage and have provided quotes for just replacing the broken components, and for replacing all the valve springs. So I'm assuming the piston, valve, and lifter are all okay somehow! I'm going to just get the head reinstalled along with a new pushrod, and a new valve spring, and hope there aren't any other bad springs in the installed batch....and that the rockers are all okay.

I would love the insurance of replacing all the springs, but their quote was equal to the cost of two fully built BTR or Ligenfelter Heads + a few hours of labor!!!!

So for long term piece of mind I'm going to invest in some new heads and just pay to get those installed....or do it myself.
 

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The Australia only bulletin for rocker arms does NOT apply to the US SS ... just look at the VIN build date range. That batch of engines with the maybe bad supplier rocker arms was AFTER SS production ended. NONE made it into US bound cars.
 
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Don't let them put stock valve springs back in. There are much better aftermarket options.
I'm not sure they'll put aftermarket stuff in and keep the warranty intact. When I had the problem with the oil pump they wouldn't put a melling pump in and honor the warranty.
 

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OP, your issue has me considering a set of PAC 1218 springs to replace the ls3 springs. I already have chromoly pushrods and straub trunnions, but I guess I didn't realize the ls3 springs were suspect. Thanks for posting and updating.
 
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