Topic: Weird piston damage - LNF - tuned, GT3071 -

[Kelu]

Hi guys, after my second trip to the circuit I got P301 - Misfire on cyl 1 and coil pack error on first cyl too.
The engine was running in 3 cylinders with a lot of smoke coming out from almost everywhere, not only from exhaust.

For more info and a video right before it happened you can find here, but everything was working great because I made a nice time on that lap and I can't identify weird sounds from the video:
http://www.kappaperformance.com/forum/index.php/topic,10558.msg178951.html#msg178951

They opened the head today and this is what they found (click on the images to expand them):
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As you can see from the pictures looks like some of the pistons got shrunk, you can see the first piston with big gaps to the cylinder wall.

Does anybody see something similar in our engines? What could cause this kind of damage.

[Jim]

How much piston to wall clearance is that Kelu? Turbo engines I've built in  the past have typically been set up with .0015" per inch times bore diameter so the LNF should be somewhere around .005" and maybe a little tighter since they're not forged. The picture looks like you've got a lot more than that but it could be my old eyes playing tricks on me. Is that engine stock or has it been rebuilt in the past?

Is the number 1 piston round or is it broken where you have it circled? Old eyes sorta makes it look like it's missing a piece there and if that's the case, detonation killed it but I don't see any marks on the top of the piston where the broke piece would have been beating it. How do the valves look?

[Kelu]

From the pictures looks like around 3mm in metric and about 0.1" and only on the exhaust side.
The engine is bone stock never open until now, about 30 000miles, it worked great, zero oil refill between services, I was driving it with 16-20 psi on the streets/circuit doing around 330-350 bhp and 23-26psi at the drag strip doing around 400-415 bhp.
The piston is round, the red circle is to point the huge gap, if you click on the pictures to see them bigger you can see even the first ring easily through the gap. As you can see by maximizing the image the surface of the piston is great, the manufacturing code stamps are easily visible.
The valves are looking very good, same for the spark plugs, no sign of too lean or too rich, they checked visually and by feeling cylinder walls and they look very good.

[DaveOC]

I have heard rumors of our engines sometimes having been manufactured with improperly gapped piston rings. When heated sufficiently the rings expand until the gap closes, and then the ring sticks in the cylinder just enough to break the piston from the ring upwards.

That is what might be the culprit here. At least that what it would look like I would think.

[Graywolf]

Kelu, Sorry for this problem,glad your driving on the circuit and appears your driving well from the video. Stock pistons and rings according to GM are only good to 300hp and maybe a little more. You probably need to resleeve the cylinders and get aftermarket stronger pistons and rings.  I was just driving down the street doing 60 mph when I blew a stock piston, no misfires just lots of smoke. Your engine sounded great on video

[Kelu]

DaveOC I didn't reached the rings stage yet because the pistons are still in the block but from the pictures the issue is with the piston itself being smaller with 3mm - 0.1".

Graywolf It was my second visit to the track, I'm still learning the track and the car, I'm far from being a performer even if I got a pretty good time. I'm thinking to aftermarket pistons and rods if the engine is open.

[LatinVenom]

Probably the damage was from the time you were drag racing, maybe you had some problems then that were not detected and over time it resulted in this failure.

[blackbirdracing]

Looks like detonation.

Heat built up around the ringland area and due to the combustion pressures was trying to escape via the top combustion ring.

[blackbirdracing]

Notice the damage to the piston around the edge of the cylinder sleeve.   You can see the pok (sp) marks...

[Kelu]

Small update, the engine is out:
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I took new pictures with pistons:
#1 - the guilty one
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Meantime the block was sent to the machine shop and they said the cylinders are off by 0.5mm so they will machine it and the tuner ordered 86.5mm Wiseco pistons. Rods should arrive in 1 week, pistons in about 2-3 weeks.

DDM engine build kit is on its way to Romania along with a thermostat - Thank you SA!!! - engine build kit contains: Timing chain tensioner, Rear main seal, Timing Cover gasket, Main Bolts, Girdle bolts, Main OEM bearings, Rod bearings, Head gasket, cam actuator bolts and ARP Head studs.

Water pump already won at the SMMM - Thank you Boss
Supertech Valve Springs on their way to Romania - Thank you Manni


I will keep you updated.

[Sol Asylum]

No problem Kelu.

PS The Professor might think you "took" a picture.   Where's he been anyway?

[Kelu]

Thanks, corrected
Barely speak with him on facebook, probably he would say: "busy"

[Kelu]

Today I visited the shop while waiting the pistons to arrive and they showed me the most damaged piston and I took some pictures:

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(click on the image to see it full size)

Now the damage is clearly visible, what it could cause such a damage?

[Critterman]

I am going to guess it got too hot because of a lean mixture.   How many different pistons were damaged?

[POS VETT]

Looks like damage due to detonation.

[Jim]

Looks like damage due to detonation.

I agree. I thought that piston looked broken when I asked about it in the second post.

[elff]

Cryo your new pistons before installing them to give them some added strength.
To me, it looks like  a detonation issue.  Maybe just a tad too aggressive of a tune.  Do you have any logs from the time just before this occurred?

[Sol Asylum]

Kelu what do the exhaust valves look like?

[Kelu]

I am going to guess it got too hot because of a lean mixture.   How many different pistons were damaged?

#1 in the picture with the most damage, #2 medium damage similar, #3 no damage, #4 minimum damage

POS VETT & Jim thank you for your opinions

Cryo your new pistons before installing them to give them some added strength.
To me, it looks like  a detonation issue.  Maybe just a tad too aggressive of a tune.  Do you have any logs from the time just before this occurred?

I didn't log the car for more than 2 years it is in this setup for more than 3 years. Cryo treating the pistons will mean at least 1 month delay and it would double the price of the pistons.

Kelu what do the exhaust valves look like?

Sorry I don't have any pictures with the head, it looked over it and was looking good (pretty much as the pistons), also I asked at the shop and they said that the head is in good condition but they need to tear it apart to install the supertech valve springs. I hope I will take some pictures in 1 week.

[Jim]

Could have been a batch of bad gas since it ran well for so many years. Depending on the amount of detonation/heat, that damage could have happened in about 10 seconds. You'll usually hear the pinging when the detonation gets that bad though.

[Sol Asylum]

Get some pictures of the valves and post them when you can.  I'd like to see if maybe they are discolored which can be a good indicator of overheating. 
 

[Kelu]

Could have been a batch of bad gas since it ran well for so many years. Depending on the amount of detonation/heat, that damage could have happened in about 10 seconds. You'll usually hear the pinging when the detonation gets that bad though.

I think it happened in 2 stages, one when going to the circuit for the second time, on the road there, I was on a country road and a friend called me that he stopped some hundreds yards back and then I stopped and reversed the car and I got the misfire for the first time while driving in reverse 30-40mph to reach that friend. Drove it with rough engine for another half a mile until the circuit where I cleared the code and it was working nice. Then I took it to the track and for the first half of a lap it threw again same 2 codes and I thought I'm going back to pit stops but on the second part of first lap is started to work ok and then I pushed it for another 5 laps with some over-reving (reaching above 7500rpm for about 2-3 times) until it cracked

Get some pictures of the valves and post them when you can.  I'd like to see if maybe they are discolored which can be a good indicator of overheating. 
 

If I remember correctly the exhaust valves were black, like the surface of the pistons.

[Graywolf]

From my understanding the engine computer will automatically detune the engine if gas octane is to low and it prevents detonation. There other causes, computer temporary glitch, timing chain,etc.  When I blew a piston I also had some back firing, at first occasional then it would go away for a while then lots of smoke end of story!  Make sure everthing is perfect on your head ,consider replacing valves with stronger after market ones,closely check all the lifters,since your in the engine open, stronger spring for the chain tightner is recommended-cheap

[Kelu]

From my understanding the engine computer will automatically detune the engine if gas octane is to low and it prevents detonation.

Yes, I saw that when tuning my car on the dyno, it was retarding the timing when it had indications from the sensors that it might detonate which was not happening actually.

There other causes, computer temporary glitch, timing chain,etc.  When I blew a piston I also had some back firing, at first occasional then it would go away for a while then lots of smoke end of story!

Sounds like mine

Make sure everthing is perfect on your head ,consider replacing valves with stronger after market ones,closely check all the lifters,since your in the engine open, stronger spring for the chain tightner is recommended-cheap

I did not plan aftermarket valves, do you have any ratings about the stock ones? Everything else on the head will be inspected when replacing the valve springs. Also I got a new chain tensioner in the engine rebuild kit from DDM.

[Graywolf]

No rating on stock valves except GM engine build book recommended up grading on similiar engine when increasing hp