Piston Ring Failure (lots of pics of inside an LNF)
 

For those who don't know, I recently had a piston ring give out on my SS/TC. The cause was ruled a manufacturing fault and the dealer was outstanding about it, being honest about the cause despite my aftermarket parts and treating me very well. Definately buying there again.

Background story... keep scrolling for the pics:
I started noticing during long trips (5 hours each way) that if I was cruising for a long time, the car would misfire and/or make a "putting" sound if I tried to get on it to pass somebody for instance. Sometimes it would be RPM dependent and sometimes just pedal dependent. After getting into town it would also have a bit of a rough idle sometimes too. I attributed it to the fuel trims skewing a lot during constant cruising for a long time at one RPM and speed. It took about a day usually around town for it to start driving fine again. It always seemed more prone to it on rainy and/or cold days.

I started having trouble if I'd NLS sometimes. It would stumble for a split second and then catch itself and keep going. I got a flashing misfire CEL a time or two.

Eventually I got a solid CEL for a misfire on cylinder 1 and took it in. The dealer did a compression test (140psi) and changed the plug and coil pack on cylinder one and the car seemed fine for about a week to a week and a half.

I eventually got a cylinder 1 misfire CEL again (flashing and then solid) and on the last day before I took it in again I started having a smoke show whenever I'd stop. Compression tested at 90psi and this time the (new) spark plug had oil on it.

They tore down the engine and at first didn't see any issues. They eventually found stress cracks in the piston between the first and second compression rings. These cracks caused the first compression ring to push up onto the bottom ledge of the top land and seize there. Then with normal usage and the piston expanding with it stuck there, the ring snapped in two places and oil started getting by, causing misfires and later smoke.

They replaced the piston/rod (they come as one), the gaskets/seals, and spark plugs. It's running great now.

Diagram to help people understand/visualize:
http://www.tpub.com/content/construc...14264_76_2.jpg

Below are pictures of the piston and others of the disassembled LNF:

Piston with one of the cracks visible (sorry it's fuzzy... camera wouldn't focus)
https://www.cobaltss.net/gallery/fil...3/100_2169.jpg

Head with valve cover
https://www.cobaltss.net/gallery/fil...3/100_2170.jpg

Inside oil pan (Made in Israel apparently, as it's stamped in there)
https://www.cobaltss.net/gallery/fil...3/100_2171.jpg

Parts that had to be removed (notice CIA CP and broken-in CIA DP)
https://www.cobaltss.net/gallery/fil...3/100_2172.jpg

Top of block and turbo
https://www.cobaltss.net/gallery/fil...3/100_2173.jpg

Inside the block and cylinders (notice the vacuum tank in front of the cylinders)
https://www.cobaltss.net/gallery/fil...3/100_2174.jpg

Other views of the turbo
https://www.cobaltss.net/gallery/fil...3/100_2175.jpg

https://www.cobaltss.net/gallery/fil...3/100_2176.jpg

Exhaust header (notice the piping division evident on the inside, for the twin scroll turbo design)
https://www.cobaltss.net/gallery/fil...3/100_2177.jpg

Intake manifold
https://www.cobaltss.net/gallery/fil...3/100_2178.jpg

https://www.cobaltss.net/gallery/fil...3/100_2179.jpg

Inside the head and various other pictures
https://www.cobaltss.net/gallery/fil...3/100_2180.jpg

https://www.cobaltss.net/gallery/fil...3/100_2181.jpg

https://www.cobaltss.net/gallery/fil...3/100_2182.jpg

https://www.cobaltss.net/gallery/fil...3/100_2183.jpg

https://www.cobaltss.net/gallery/fil...3/100_2184.jpg

https://www.cobaltss.net/gallery/fil...3/100_2185.jpg

https://www.cobaltss.net/gallery/fil...3/100_2186.jpg

Direct Injection fuel rail and injectors
https://www.cobaltss.net/gallery/fil...3/100_2187.jpg

Some great pictures.

You have the same issue i just had... i have a lsj tho with 30k on it

Mine just rolled over 30k too.

I do a lot of long trips across TX to see family.

OP hope everything continues running great for you.

Thanks alot for the pics!

It's not abnormal to crack ringlands on cast pistons if there's too much boost, or too much knock. Did you have a custom tune to support all those mods?

Warren

notice the color at the top of cylinder one. did the tech say that is normal. and not sure if it is a reflection or something with the picture, but look at cylinder three. looks like scoring in the cylinder. just looked at another pic and seen the score marks in that one also. have them make sure that cylinder is fine

Sorry to hear about the trouble

Wonderful pictures....I have been wanting to see a lot these images for the LNF

odd note: the LNF apparently has two knock sensors...

Agreed. I think the only way to fix that block is to bore it out to the next size up. They should have 2 sizes for pistons from GM. Anything short of this, plus a re-tune, will lead to more heartache, I'm afraid.

Warren

That color at the top of cylinder one was the unburnt oil built up on the cylinder wall that was getting past the piston. All four of us (two techs, service advisor, and briefly myself) checked the cylinders and didn't see any scoring or anything out of the ordinary, in fact even cylinder one had no wear marks at all from the seized ring. I made sure to ask them about potential scoring (although it only pertained to cylinder one). I think it shows up like that in more than one picture because they were taken from a similar point of view and there was some oil that had gotten on things, but I'll ask them again about it to make sure. Thanks, good eye.

The dealer didn't mention your tune or anything?

Nope. They did call me and tell me that the IC they installed ~9months ago, when my stocker's endcap broke, somehow increased power by 60HP though. :lol: If there was an IC on the market that instantly increased power by 60HP all the time, then count me in. The price Hahn charged for mine would definately be worth it then. ;)

I think what happened is they were test driving it and accidentally activated the tune while they had the RPD switched to the HP and Torque screen because when I got it back the tune was active and the RPD was switched to that page. :lol:

Honestly though, since this was a manufacturing defect, then that shouldn't matter anyway.

sorry to hear about the trouble but thanks for the detailed pics.

Man the intake ports look a lot smaller than the other Ecotec heads do. They rounded off the port floor for some reason...... Great pics! The stock turbo is so small and quaint!!

was it covered under warranty?

I would send Vince the bill ...

If your dealer is covering that under warranty I would be a customer for LIFE!!!!!! I would preach there name to every one that needs a new car. The dealer that I use here(moritz chevrolet) seems pretty cool but damn yours is AWESOME.

i have the same issues and think this may be going on as well. now is it safe to be boosting so much on the car? im hitting 28k on my car, maybe we are the first to see these issues cause all the miles we have put on them with tunes? granted my initial tune was bad, brings up the question of how much should we actually be boosting and pushing these cars? my dealer are fukn dick and never warrenty shit so im sure im getting shafted when i take it in.

Keep an eye out on KR on the RPD, and your oil consumption. Sorry, but #3 is scored. It shows up in every single shot you took. I would suspect the ringlands on 3 are also cracking. It's possible for them to go without knock going up much. A leakdown test will tell the truth. I'd put money that #3 fails a leakdown/comp.

The truth is that no one should be running custom tunes without logging knock sums or knock retard. Without forged pistons, all it takes is 87 octane gas, and an aggressive tune to start a thread like this.

http://en.wikipedia.org/wiki/Hypereutectic_piston

"The biggest drawback of adding silicon to pistons is that the piston becomes more brittle as the ratio of silicon is added. This makes the piston more susceptible to cracking if the engine experiences pre-ignition or detonation."

I came from a Subaru, where that's all people were talking about, and even after laying down over 375 whp and 94k miles, I was paranoid of it happening to me. The LNF is more resilient than that, but it's still hypereutectic pistons in there. At least it's alot easier to rebuild the engine than the oddball boxer arrangement.

Warren

i sure hope this is not what is happening to my car.. we shall see i guess. i will be doing a compression test this weekend to see where i'm at. thanks for posting the pics!

The sad thing is I rarely use the tune. I drive 90-95% in stock tune. A local tuner and I logged the crap out of the tune two times, spending a couple hours each time. I've got logs, but they're pretty much knock-free. I wonder if the stock tune could be the culprit. It seems at partial throttle in some places and WOT stock tunes have been shown to knock sometimes. Maybe we need to poll classic Trifecta tuned people (the ones where it's always on) and see if they've been having any trouble. I may want to go log my stock tune now too as I don't think I've done that.

My RPD has always shown 0* KR in any tune mode to my knowledge, so I don't have much confidence in it unless traditional logging is just picking up phantom knock. The IC looks to really keep the IAT2s down in the logs, so that's promising.

The stock tune does knock like crazy even on 93 octane. You guys have only 91 octane out there in Texas so I can only imagine how badly the stock tune must knock out there. Excessive knock will cause cracking like that to happen. Excessive pressure on the rings from running excessively rich could also stress the rings and the ring lands.

sounds like these cars are bullshit

wow that sucks