LS2 piston failure
07-27-2009, 08:07 PM
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LS2 piston failure the car:
05 GTO M6 (24k miles 15k as built)
the mods:
Livernois 3r heads, Comp XER281 (232/234 595/598), Harland Sharp 1.7 roller rockers, FAST 90, Pacesetter l/t w/ mids, ported t/b, Corsa Sport exhaust ~460rwhp N/A no juice and no track time
the story:
rolled into wot and at 5500 heard a clattering type of sound then the car lost some power. instantly i got out of it. i thought the clutch slipped at first until i stopped at a red light and heard what sounded like a ball peen hammer hitting the side of the engine. drove it home easy (about 2 miles to my house), put it in the garage and attempted to locate source of noise. sounded like it was coming from everywhere but more noticeable on driver side and horrible under the car. it seemed to be running fine other than the knocking sound, no missing no smoke. turned off and prayed.
fired it up the next morning for about 30-45 seconds for a friend to hear and it was quiet. i even reved it to about 2000 and the most noise i could make out was what sounded like the typical piston slap. he did agree the the driver side seemed to be a little louder.
pulled heads on friday night.
the damage: (fyi this is #7)
#5 for comparison
i know there is a lot of knowledge here on this board so besides being royally f'ed, what you guys think happened? what are the odds of #7 bearing being bad?
i did drain the oil and let it flow over a magnet and nothing was on it when done. also the cylinder wall looks good too.
looking for some info, thanks...
05 GTO M6 (24k miles 15k as built)
the mods:
Livernois 3r heads, Comp XER281 (232/234 595/598), Harland Sharp 1.7 roller rockers, FAST 90, Pacesetter l/t w/ mids, ported t/b, Corsa Sport exhaust ~460rwhp N/A no juice and no track time
the story:
rolled into wot and at 5500 heard a clattering type of sound then the car lost some power. instantly i got out of it. i thought the clutch slipped at first until i stopped at a red light and heard what sounded like a ball peen hammer hitting the side of the engine. drove it home easy (about 2 miles to my house), put it in the garage and attempted to locate source of noise. sounded like it was coming from everywhere but more noticeable on driver side and horrible under the car. it seemed to be running fine other than the knocking sound, no missing no smoke. turned off and prayed.
fired it up the next morning for about 30-45 seconds for a friend to hear and it was quiet. i even reved it to about 2000 and the most noise i could make out was what sounded like the typical piston slap. he did agree the the driver side seemed to be a little louder.
pulled heads on friday night.
the damage: (fyi this is #7)
#5 for comparison
i know there is a lot of knowledge here on this board so besides being royally f'ed, what you guys think happened? what are the odds of #7 bearing being bad?
i did drain the oil and let it flow over a magnet and nothing was on it when done. also the cylinder wall looks good too.
looking for some info, thanks...
07-27-2009, 08:39 PM
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a local guy who now works at well known speed shop in DFW. i don't know any details of the tune unfortunately. i can get that from him or i'm sure someone could pull it off of my computer.
i will say i was chasing lean issues off and on for quite a while and he tweaked it about 3 different times after the inital street tune when i took off my shorties and added l/t. it had goten to the point where it throw lean codes if sat at idle for too long, LTFTs would slowly start to scale out when sitting. it would surge when warm stared and most times would die if i didn't give it some gas. i thought i had that fixed the last time he tweaked the tune, i think he said he turned off the LTFTs and they read 0. the surge and warm start issue was gone too, no problems at all after that. it hadn't thrown a lean code in a couple of months and i had quit monitoring the trims. i asked him a little later about the LTFTs being off and if it would throw a lean code if indeed it was running lean, he said it would and went on thinking everything was good. well, here we are today and i'm looking for explanations.
i will say i was chasing lean issues off and on for quite a while and he tweaked it about 3 different times after the inital street tune when i took off my shorties and added l/t. it had goten to the point where it throw lean codes if sat at idle for too long, LTFTs would slowly start to scale out when sitting. it would surge when warm stared and most times would die if i didn't give it some gas. i thought i had that fixed the last time he tweaked the tune, i think he said he turned off the LTFTs and they read 0. the surge and warm start issue was gone too, no problems at all after that. it hadn't thrown a lean code in a couple of months and i had quit monitoring the trims. i asked him a little later about the LTFTs being off and if it would throw a lean code if indeed it was running lean, he said it would and went on thinking everything was good. well, here we are today and i'm looking for explanations.
07-27-2009, 09:50 PM
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I think you may be pretty lucky. New pistons, have the head looked at, bolts/gaskets, and some time and labor. Of course take a real good look at that cylinder too and make sure it's not messed up. It could have been much worse.
07-27-2009, 09:58 PM
#6
I bought a LS2 that had a problem with number 7....The pushrod was bent and the exhaust valve wouldn't seat...Tore the whole thing apart and there was a shard of glass on top of the lifter along with a odd looking piece of wire...( not from the valve ) Don't ask me how that stuff got in there either...and on the crank journal there was a small pit...Everything else looked fine.. I would also say you're lucky if there is no other damage...
07-28-2009, 06:25 AM
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well i've got to get the engine out, tear it down and examine the crank and bearing. i'm hoping that it's ok but at the same time i'm hoping it's not (wallet just punched me in the head).
as far as the tune i don't know anything. guess i didn't ask enough questions. i want i to say wot afr is 13 but i don't know for sure because it was a street tune and i was driving. i also think he had a lot of timing in it too, but still unsure of specifics.
as far as the tune i don't know anything. guess i didn't ask enough questions. i want i to say wot afr is 13 but i don't know for sure because it was a street tune and i was driving. i also think he had a lot of timing in it too, but still unsure of specifics.
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07-28-2009, 06:48 AM
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Hi sergo, mine broke no 5 to but it was 11:1 comp and 9 psi boost. afrs were 11.5:1 timing conservative.
No 1 thing to remember is that cylinder no 7 definately runs richer then the others obviously due to airspeed or lack of, you can see by ur pics on the ex valve it is rich. The standard pistons wont tolerate as much heat as a forged piston at hi temps and pressures they are like glass. In order to ensure you dont have a lean cylinder(more common in 5,7,4,6,) just check the plugs, obviously your was rich which tends towards a timing related detonation issue. I have never seen an NA one break which I have tuned anyway. FI you have to tune safe but not to rich low 11s but if it is that rich it kills power may aswell go forged internals.With FiTo rich u wash ur bores AND loose power from being optimum afr pull too much timing out your ex temps rise dramatically.So decomp or bigger cam is the go but with NA its more leanient. My bet it had some detonation to do that. with those heads and that comp if you are going much over 25-26 deg up top and 20-22 peak torque it wont live.Also keep afr 12.5:1-12.8:1 . Usually NA u have more leeway but this is simply to much spark.
No 1 thing to remember is that cylinder no 7 definately runs richer then the others obviously due to airspeed or lack of, you can see by ur pics on the ex valve it is rich. The standard pistons wont tolerate as much heat as a forged piston at hi temps and pressures they are like glass. In order to ensure you dont have a lean cylinder(more common in 5,7,4,6,) just check the plugs, obviously your was rich which tends towards a timing related detonation issue. I have never seen an NA one break which I have tuned anyway. FI you have to tune safe but not to rich low 11s but if it is that rich it kills power may aswell go forged internals.With FiTo rich u wash ur bores AND loose power from being optimum afr pull too much timing out your ex temps rise dramatically.So decomp or bigger cam is the go but with NA its more leanient. My bet it had some detonation to do that. with those heads and that comp if you are going much over 25-26 deg up top and 20-22 peak torque it wont live.Also keep afr 12.5:1-12.8:1 . Usually NA u have more leeway but this is simply to much spark.
07-28-2009, 03:53 PM
#9
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Looks like typical detonation damage to me, just look at the quench pads compared to the chamber. I've seen this a few times on cars over here running with aftermarket management. Sometimes they even have dents/notches in the quench pads when it's really bad. Pistons can't survive that. Fuelling doesn't look bad but you drove it for a while so who can be certain about that. What are the insulators like for the 1 mm under the earth electrode of the plug? Do they look white and hot or do they have carbon on them?
I had an engine here with a problem like this but worse caused by a customer having his coolant header tank lower then the cylinder heads.
I had an engine here with a problem like this but worse caused by a customer having his coolant header tank lower then the cylinder heads.
07-28-2009, 09:14 PM
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thanks for the info guys, i'm getting a lot more here than on the other one i vist frequently.
hymey, i wish i knew what the timing was in the car but i didn't ask enough questions while it was getting tuned. but, your saying it was rich instead of lean and may have had alot of spark advance? interesting... i do think the afr was around 12.8-13.0.
boosted, hate to say it but i have no idea what you're talking about. please explain so i can understand. and the plugs, i haven't looked real close at them but i will. i know which one is #7, it's the one that still has a tiny piece of piston still stuck to it.
thanks for the info, please by all means keep it coming. i want to know and understand.
hymey, i wish i knew what the timing was in the car but i didn't ask enough questions while it was getting tuned. but, your saying it was rich instead of lean and may have had alot of spark advance? interesting... i do think the afr was around 12.8-13.0.
boosted, hate to say it but i have no idea what you're talking about. please explain so i can understand. and the plugs, i haven't looked real close at them but i will. i know which one is #7, it's the one that still has a tiny piece of piston still stuck to it.
thanks for the info, please by all means keep it coming. i want to know and understand.
07-29-2009, 12:23 PM
#11
Hi sergo, mine broke no 5 to but it was 11:1 comp and 9 psi boost. afrs were 11.5:1 timing conservative.
No 1 thing to remember is that cylinder no 7 definately runs richer then the others obviously due to airspeed or lack of, you can see by ur pics on the ex valve it is rich. The standard pistons wont tolerate as much heat as a forged piston at hi temps and pressures they are like glass. In order to ensure you dont have a lean cylinder(more common in 5,7,4,6,) just check the plugs, obviously your was rich which tends towards a timing related detonation issue. I have never seen an NA one break which I have tuned anyway. FI you have to tune safe but not to rich low 11s but if it is that rich it kills power may aswell go forged internals.With FiTo rich u wash ur bores AND loose power from being optimum afr pull too much timing out your ex temps rise dramatically.So decomp or bigger cam is the go but with NA its more leanient. My bet it had some detonation to do that. with those heads and that comp if you are going much over 25-26 deg up top and 20-22 peak torque it wont live.Also keep afr 12.5:1-12.8:1 . Usually NA u have more leeway but this is simply to much spark.
No 1 thing to remember is that cylinder no 7 definately runs richer then the others obviously due to airspeed or lack of, you can see by ur pics on the ex valve it is rich. The standard pistons wont tolerate as much heat as a forged piston at hi temps and pressures they are like glass. In order to ensure you dont have a lean cylinder(more common in 5,7,4,6,) just check the plugs, obviously your was rich which tends towards a timing related detonation issue. I have never seen an NA one break which I have tuned anyway. FI you have to tune safe but not to rich low 11s but if it is that rich it kills power may aswell go forged internals.With FiTo rich u wash ur bores AND loose power from being optimum afr pull too much timing out your ex temps rise dramatically.So decomp or bigger cam is the go but with NA its more leanient. My bet it had some detonation to do that. with those heads and that comp if you are going much over 25-26 deg up top and 20-22 peak torque it wont live.Also keep afr 12.5:1-12.8:1 . Usually NA u have more leeway but this is simply to much spark.
Gerry
07-30-2009, 06:44 PM
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08-06-2009, 08:07 PM
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here are a couple of the past (before l/t and ported t/b) maf/pe tune tables and after (with l/t and ported t/b) tables. the last spark table is there too. also know that the after tune is also after 3 prior trips to resolve some lean idle and erratic warm start issues.
what do you guys think?
here's link to my thread on ls1gto if any one cares
http://www.ls1gto.com/forums/showthread.php?t=326171
what do you guys think?
here's link to my thread on ls1gto if any one cares
http://www.ls1gto.com/forums/showthread.php?t=326171
