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Blew Piston rebuilt forged engine

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Old 09-12-2017, 09:31 PM   #1
CharlieC5Z06
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Default Blew Piston rebuilt forged engine

So as some of you know I had my 2002 z06 engine rebuilt with a forged 383 stroker a month ago. I did it because I broke a piston in the stock engine. I put all forged Texas speed internals with Mahle pistons.

Everything in the engine is new. Only thing i left the same were the TREperformance 80lb injectors.

My tuner safely tuned it a couple weeks ago but I had to fix an exhaust leak before the dyno pulls. Fixed the leak and drove it for a week before today and it drove great. Didnt get into any crazy pulls on the street but did get it up to 10psi in 3rd gear at one point. (D1SC Procharger)

So today on the dyno during the first pull the tuner noticed that the afr was reading lean but he said it must be wrong because hes giving it alot of fuel on the first pull. The numbers were really low but he said it must be wrong because the car felt good. At first he thought the software was messed up on his dyno. Tried a couple more pulls then on one pull all of a sudden white smoke out of the exhaust and out of the oil cap breather.

Took it off the dyno and started it again and it was backfiring like crazy. He took the temp on the headers and one cylinder was way colder than the rest. I tried to drive it home slowly to start trouble shooting but it got bad so I pulled over and got a tow

Got home and checked the spark plugs and the one in the low temp cylinder was gunky and the electrode was bent and touching the plug.

Milky oil on dipstick and in the oil cap breather.

I pulled the head off and I indeed cracked off a chunk of the piston. Cylinder wall looks fine and the ls9 head gasket looks fine.

Where is the coolant getting into the oil?

Could I have one bad injector that destroyed my last cylinder and this one as well?

I am so depressed right now. I put sooo much time and money in this car this summer and barely got to drive it. I installed a lift in my garage and tried to do everything right. I guess I shouldnt have cheaped out on the injectors.

Any input would be great.

Thanks
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Old 09-12-2017, 10:02 PM   #2
Kevova
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Detonation? It takes a lot of coolant to break a piston, I would expect the rod would fail first.
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Old 09-12-2017, 10:10 PM   #3
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tune it back to stock,and leave the damned ''kiddy cars'' to people that don't want to drive their cars,,o'ya get a better dyno guy next time
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Old 09-12-2017, 10:14 PM   #4
CharlieC5Z06
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Yeah must have been detonation. But not sure where the coolant came from. The gasket looks fine. Don't see any cracks in the head.

Wasnt getting any knock either.

I honestly have no clue what's going on.
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Old 09-13-2017, 09:19 AM   #5
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just because you dont see a crack does not mean there is not one.. if it were me i would disassemble and have the block checked out.. but that is me of course. hope you get it where you want. keep us posted.
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Old 09-13-2017, 09:24 AM   #6
CharlieC5Z06
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Yeah I am going to have the heads checked out and possibly just buy new ones but I really dont want to pull the engine out again. I am going to take that piston out and check the cylinder walls and if it looks good. I am going to just replace the one piston.

I literally had this engine rebuilt a month ago. Maybe 150 miles on it. I just dont understand how it felt like it was running fine but then all of a sudden blow up. Could one injector not have been working at all and I have been running on 7 cylinders and the car feel fine then after a couple of hard dyno pulls it just had enough? I am going to buy ID1000 injectors after I get the piston changed.
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Old 09-13-2017, 11:08 AM   #7
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You could send the injectors out to be cleaned and flow tested. If one is dead they'll be able to tell.

Which cylinder has the broken piston now? Not #7 is it? (driver side rear piston)

But I send my deepest sympathies. I'm in the process of rebuilding my motor right now too. (I broke the #7 piston). My biggest fear is that I get it all back together and run into a serious issue like you have. I've been down that road before with my 2V 4.6L in my Mustang. Rebuilt the motor, all forged internals yada yada... 1500 miles later it lost oil pressure... every main bearing was wiped. (but it did make 615rwhp on 17psi tho).
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Old 09-13-2017, 11:15 AM   #8
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id be checking the cyl for cracks also..when he saw it was lean and down on power should have stopped right there not just keep pulling hoping it goes away, good gawd. Bad situation
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Old 09-13-2017, 01:00 PM   #9
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Yeah it was number 7. I just spoke to an injector place near me. He's gonna flow test them for free. Once I said they were TRE injectors he said oh no. They are the worst. So I said throw them out when your done.

I really really hope the cylinder is ok. My machinist said he would come by and check it out after I pulled the piston to see if it's still good.

Why didnt I leave it stock? Lol. Money spending never ends.
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Old 09-13-2017, 01:16 PM   #10
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#7 is a very common failure.

Do you have the rear steam ports open or are they blocked off? I wonder if you had an air pocket in the coolant and boiled the fluid? that overheats the cylinder and it's easy to bust a piston.

Any idea what ring gap you had? I read an older thread on the #7 cylinder failures, and a Trickflow tech posted a suggestion of opening up the ring gaps for the rear cylinders. He posted his gap recommendations but I don't recall them off-hand.

Any pictures of the failed piston?
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Old 09-13-2017, 01:22 PM   #11
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Rear ports are closed. No clue about the ring gap.
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Old 09-13-2017, 01:39 PM   #12
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Yep, that's where all #7 pistons fail.

The theory on the ring gaps was that the ring ends butt and lift upward, either cracking the piston top or the ringlands. So opening up the ring gap gives more room for error before this happens.

I would recommend opening up the steam vent ports. Trickflow makes a nice kit for $140. Or you can use a later truck style crossover (GM # 12605716 - $34) and run a piece of coolant hose and tie in with the front crossover line.
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Old 09-13-2017, 01:44 PM   #13
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OK thanks, Can you tell if a ringland was broken from that picture? It looks like its just the top of the piston. Hoping the cylinder walls are ok.

What does opening the steam vent do?
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Old 09-13-2017, 02:48 PM   #14
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Can't see the ringland until you pull the piston out.

Attached is a picture of what my broken piston looked like. Broken the ringland, but not the face of the piston.

Opening up the rear steam ports always any air pockets to circulate out of the system. Otherwise they can get trapped in the back corners. An air pocket will allow a localized hot.

There's a ton of reading and theories on why the #7 cylinder is so prone to failure but there doesn't seem to be a definitive answer. So my approach is do anything you can to help the situation. The reason I'm going with forged pistons is just for extra insurance against this. Sad to see your forged piston still failed.

I'm going with JE pistons which are a 2618 forging vs the Mahle's which are a 4032 forging. The 4032 would be a bit more brittle, but still should have been up to the task.
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Old 09-13-2017, 03:09 PM   #15
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Finally found the thread I was looking for that mentioned the ring gaps.

https://ls1tech.com/forums/road-raci...ine-build.html

Trickflowtech suggested... "The factory ring gaps are tight and opening up the gap on 7 a bit more than the others is a good idea. Probably .018 on the top and .023 2nd would be a good starting point."
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Old 09-14-2017, 02:30 PM   #16
Bill Curlee
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Looks like a RING GAP Issue.

Put the old rings inside the cylinder and see what they measure. That will give you an idea where to start on the new ring gap.

Please post what the gaps were.

Bil
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Old 09-14-2017, 02:40 PM   #17
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Thanks guys.

The thing that makes me think that its more than just ring gaps is because of the lean reading and the only things that are the same on the two engines were the injectors. Im getting them tested next week to see if the one malfunctioned.

Im going to pull the piston this weekend so Ill have more updates sunday.

Thanks again.
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Old 09-14-2017, 07:43 PM   #18
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If the ring gap is wrong, I would get with the machine shop who did the work and set them up wrong and see what they will do to make it right.
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Old 09-14-2017, 07:47 PM   #19
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Quote:
Originally Posted by cuisinartvette View Post
id be checking the cyl for cracks also..when he saw it was lean and down on power should have stopped right there not just keep pulling hoping it goes away, good gawd. Bad situation
yeah, software issue???? sounds like he shouldn't be tuning a lawnmower
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Old 09-14-2017, 10:40 PM   #20
CharlieC5Z06
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My machine guy is pretty **** and from what I hear he is the best around. He's not a huge ls guy though but he went by the book on mine. He mainly builds huge $50,000 plus dirt modified engines.

Even if the gap was wrong i must have another issue that was causing that cylinder and possibly other cylinders to run lean. That's why I'm hoping my injectors are bad so i can narrow down my issues for when I redo this thing.
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