Melted Pistons - Help
May 11, 2004, 07:23 PM
#32
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that looks like preignition, generaly, detonation will damage the center of the piston as detonation is the effect when 2 flame fronts collide. preignition will usualy brake ring lands like that and sometimes melts the pistons.im surprised you didnt see any higher temps from your egt's id study your datalog again and make sure your timing wasnt advanced to much at some point. or perhaps you got some poor gas.
a bad injector will not cause a lean mixture, only a clogged injector if an injector has a problem with in the curcuit it will just not fire and youll have no fuel and a missfire, no damge such as that.
a bad coil will again just cause no spark and a missfire, not damage such as that.
also a problem such as those would cause an obvious change in the a/f ratio, it would go extremely rich.
your problem seems to be an issue of improper a/f ratio or improper ignition timing.
also theres a chance something could have gotten extremly hot in the cyl maybe a burr on the piston or a carbon build up. which ignited the mixture early.
again its just my opinion, but its looks like preignition to me.
a bad injector will not cause a lean mixture, only a clogged injector if an injector has a problem with in the curcuit it will just not fire and youll have no fuel and a missfire, no damge such as that.
a bad coil will again just cause no spark and a missfire, not damage such as that.
also a problem such as those would cause an obvious change in the a/f ratio, it would go extremely rich.
your problem seems to be an issue of improper a/f ratio or improper ignition timing.
also theres a chance something could have gotten extremly hot in the cyl maybe a burr on the piston or a carbon build up. which ignited the mixture early.
again its just my opinion, but its looks like preignition to me.
May 11, 2004, 10:38 PM
#33
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two things catch my attention:
1. only one piston is melted... how are the other 3?
2. look at your ring and piston side, they were melted not nessesarily broken... so me it looks warped.
ive seen this type of thing on a melted deisel piston before. this is obviously way to much heat. almost every time pistons melt in a diesel its from oil problems ( oil not cooled enough, insufficient oil flow, etc.). i know this isnt a diesel (so dont correct me) but this just looks similar. with detonation, from what ive seen in the past, there is pieces of metal embeded into the piston (looks like a crater). i dont see any on that one. if the other 3 pistons are not in bad shape, id be willing to bet theres a problem with some delivery system, or mechanism corresponding with that particular cylinder. how do the cylinder walls look? its wierd you didnt notice any abnormally high egt's, the kind of heat needed to do this work would even be high for where your egt probe is. however, i heard it can be more than a 100 degree difference between the two placements before and after turbine. its purplexing without much more info.
1. only one piston is melted... how are the other 3?
2. look at your ring and piston side, they were melted not nessesarily broken... so me it looks warped.
ive seen this type of thing on a melted deisel piston before. this is obviously way to much heat. almost every time pistons melt in a diesel its from oil problems ( oil not cooled enough, insufficient oil flow, etc.). i know this isnt a diesel (so dont correct me) but this just looks similar. with detonation, from what ive seen in the past, there is pieces of metal embeded into the piston (looks like a crater). i dont see any on that one. if the other 3 pistons are not in bad shape, id be willing to bet theres a problem with some delivery system, or mechanism corresponding with that particular cylinder. how do the cylinder walls look? its wierd you didnt notice any abnormally high egt's, the kind of heat needed to do this work would even be high for where your egt probe is. however, i heard it can be more than a 100 degree difference between the two placements before and after turbine. its purplexing without much more info.
May 11, 2004, 11:05 PM
#34
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Ok I have to agree with the last two posts. What I want to see is the log. You were logging the run, right? You need to take a hard look at the log right at the 4000 RPM point. This is just about the the most load point of the car. How much timing was there at that point. In my maps I have no more than 12-14 degrees of timing at that point. Once after the 5000 rpm point I start puting in a bunch of timing.
I would realy like to look at the logs.
I would realy like to look at the logs.
May 12, 2004, 12:47 AM
#35
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Did not take a photo of the plug. But it was not burnt up. Just that a part of the porcelain portion was chipped off leaving a slight depression.
Originally Posted by Incognito
How did the spark plug look in that cylinder? Was it totally
burnt up? Maybe slight detonation make the tip of the plug chip off, therefore expanding the gap.
A/F in the 11:1 range running 24psi isn't anything crazy, even if it's on pump gas. Maybe check your coil to see if the ignition system is up to par. Maybe that one cylinder was firing whern it wasn't supposed to.
burnt up? Maybe slight detonation make the tip of the plug chip off, therefore expanding the gap.
A/F in the 11:1 range running 24psi isn't anything crazy, even if it's on pump gas. Maybe check your coil to see if the ignition system is up to par. Maybe that one cylinder was firing whern it wasn't supposed to.
May 12, 2004, 12:51 AM
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It is a jap piston from Jun. Forged and coated.
The melting occured on the intake side of the piston. Because of the melted piston there was some minor scuffing on the cylinder wall of the 4th cylinder. Other than that the rest of the engine (everything was strengthened though before) was ok.
What is puzzling is that the EGT readings was max 720 degrees (sensor on beginning of downpipe just after O2 housing)
The melting occured on the intake side of the piston. Because of the melted piston there was some minor scuffing on the cylinder wall of the 4th cylinder. Other than that the rest of the engine (everything was strengthened though before) was ok.
What is puzzling is that the EGT readings was max 720 degrees (sensor on beginning of downpipe just after O2 housing)
Originally Posted by joeycoates
I agree with incognito, 11:1 and 24lbs does not sound all that crazy, actually not very crazy at all. That is well with in the "rich" side of safe. Maybe the timing was advanced enough to be on the treshold of knock, but high enough so that the cylinder pressure was just too high? Raising the cylinder pressure to the point where you are right under knock is good for a quick torque hump, but it is really hard on the internals. What piston make is that? I cannot tell, but I would assume that this is on the exhaust side of the piston? Those would be some high EGT's to melt it like that. How much damage did it do to the rest of the engine?
May 12, 2004, 12:55 AM
#37
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The rest of the pistons are not melted. but to me it seems there is a gradual heat damage from 1 to 4 as in 1's piston was perfectly fine, 2's piston shows some heat as slightly wearing of the coating. 3's piston shows more wearing of coating and if i am to guess, it is about to melt soon.
The ignition at 4000 rpm load point was 12 and from there it starts creeping up to 21 or 22 at rpm above 6000.
The ignition at 4000 rpm load point was 12 and from there it starts creeping up to 21 or 22 at rpm above 6000.
Originally Posted by lilgsx
Ok I have to agree with the last two posts. What I want to see is the log. You were logging the run, right? You need to take a hard look at the log right at the 4000 RPM point. This is just about the the most load point of the car. How much timing was there at that point. In my maps I have no more than 12-14 degrees of timing at that point. Once after the 5000 rpm point I start puting in a bunch of timing.
I would realy like to look at the logs.
I would realy like to look at the logs.
May 12, 2004, 01:00 AM
#38
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If it is preignition in my case then what happened or caused it? I have to solve this prob before i start driving the car again 
Originally Posted by projekzero
that looks like preignition, generaly, detonation will damage the center of the piston as detonation is the effect when 2 flame fronts collide. preignition will usualy brake ring lands like that and sometimes melts the pistons.im surprised you didnt see any higher temps from your egt's id study your datalog again and make sure your timing wasnt advanced to much at some point. or perhaps you got some poor gas.
a bad injector will not cause a lean mixture, only a clogged injector if an injector has a problem with in the curcuit it will just not fire and youll have no fuel and a missfire, no damge such as that.
a bad coil will again just cause no spark and a missfire, not damage such as that.
also a problem such as those would cause an obvious change in the a/f ratio, it would go extremely rich.
your problem seems to be an issue of improper a/f ratio or improper ignition timing.
also theres a chance something could have gotten extremly hot in the cyl maybe a burr on the piston or a carbon build up. which ignited the mixture early.
again its just my opinion, but its looks like preignition to me.
a bad injector will not cause a lean mixture, only a clogged injector if an injector has a problem with in the curcuit it will just not fire and youll have no fuel and a missfire, no damge such as that.
a bad coil will again just cause no spark and a missfire, not damage such as that.
also a problem such as those would cause an obvious change in the a/f ratio, it would go extremely rich.
your problem seems to be an issue of improper a/f ratio or improper ignition timing.
also theres a chance something could have gotten extremly hot in the cyl maybe a burr on the piston or a carbon build up. which ignited the mixture early.
again its just my opinion, but its looks like preignition to me.
May 12, 2004, 06:07 AM
#39
Ever wonder why pistons dont melt when the melting point of aluminum is only 660c? The exhaust temps regularly at well over 800c means combustion temps are well above 1000c range.
They dont melt because there is a boundery layer at the surface. Drive down the road at 70mph and watch raindrops crawl up your windsheild at 10mph. The 70mph air doesn't reach the glass because of the boundary layer.
Detonation breaks down the boundary layer and allows the heat to pass into the piston. Both the factory piston and aftermarket forged pistons are made of aluminum. They both can tolerate short bursts of detonation. The aftermarket can take more of course. But both will melt when detonation is allowed to occur long enough. From your description of the other pistons it is obvious that the engine was detonating. The one that melted first was just leading the way.
They dont melt because there is a boundery layer at the surface. Drive down the road at 70mph and watch raindrops crawl up your windsheild at 10mph. The 70mph air doesn't reach the glass because of the boundary layer.
Detonation breaks down the boundary layer and allows the heat to pass into the piston. Both the factory piston and aftermarket forged pistons are made of aluminum. They both can tolerate short bursts of detonation. The aftermarket can take more of course. But both will melt when detonation is allowed to occur long enough. From your description of the other pistons it is obvious that the engine was detonating. The one that melted first was just leading the way.
May 12, 2004, 06:18 AM
#40
The statement that detonation is at the middle of the piston is very wrong. It always occurs at the edge of the piston on the intake side. The income air/fuel charge always spews plenty of fuel on the exhaust side. Fuel being heavier that air it tends to be centrifuged toward the exhast side. Leaving the intake side lean of fuel.
The top of the cylinder head near the gasket shows wear the detonation was occuring. Burning aluminum clearly evident. The old fassion way to check for detonation is to read your spark plugs. Those tiny specs of aluminum can be seen on the base of the spark plug. If you see specs on a full throttle run. Turn the boost down.
The top of the cylinder head near the gasket shows wear the detonation was occuring. Burning aluminum clearly evident. The old fassion way to check for detonation is to read your spark plugs. Those tiny specs of aluminum can be seen on the base of the spark plug. If you see specs on a full throttle run. Turn the boost down.
May 12, 2004, 10:03 AM
#41
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awd you are correct on alot of things but i believe your confused about detonation.
detonation is when two flame fronts collide. usualy one from preignition and another from the spark. detonation usualy damages the piston somewhere in the center, because this is where the flame front will generaly collide.
u must first have preignition to have detonation, but the damage caused by preignition is different. preignition will cause great amount of more heat damage.
i went and grabbed my old tech book this is read from it
"preignition damage is charactorized by melting of the electrodes or chipping of the electrode tips, when the problem occurs, look for the general causes of engine overheating, including over -advanced ignition timing, a burned head gasket, and useing too low fuel octane, other possabilitites include loose plugs or using plugs of a improper heat range".
detonation damage will look more like someone hit the piston with a hammer as thats basicaly the effect it has ona piston.
my point is this detonation is a byproduct of preignition, but generaly it causes damage in the center of the piston as this is were the flame fronts will collide, ive seen it shatter pistons and even punch holes right throught the center of pistons
theres is a good chance this guys car detonated but to me it doesnt seem as tho the detonation took out the piston but the preignition which would have cause the detonation did
your also right on the boundary layers also but preignition will also cause greater heats to the pistons as there will a longer period of time for heat to transfer through the boundary layer. u might be right tho on the point detonsation broke down the boundary layer enough for the piston to melt, but the damage is not from detonation
detonation is when two flame fronts collide. usualy one from preignition and another from the spark. detonation usualy damages the piston somewhere in the center, because this is where the flame front will generaly collide.
u must first have preignition to have detonation, but the damage caused by preignition is different. preignition will cause great amount of more heat damage.
i went and grabbed my old tech book this is read from it
"preignition damage is charactorized by melting of the electrodes or chipping of the electrode tips, when the problem occurs, look for the general causes of engine overheating, including over -advanced ignition timing, a burned head gasket, and useing too low fuel octane, other possabilitites include loose plugs or using plugs of a improper heat range".
detonation damage will look more like someone hit the piston with a hammer as thats basicaly the effect it has ona piston.
my point is this detonation is a byproduct of preignition, but generaly it causes damage in the center of the piston as this is were the flame fronts will collide, ive seen it shatter pistons and even punch holes right throught the center of pistons
theres is a good chance this guys car detonated but to me it doesnt seem as tho the detonation took out the piston but the preignition which would have cause the detonation did
your also right on the boundary layers also but preignition will also cause greater heats to the pistons as there will a longer period of time for heat to transfer through the boundary layer. u might be right tho on the point detonsation broke down the boundary layer enough for the piston to melt, but the damage is not from detonation
Last edited by projekzero; May 12, 2004 at 11:16 AM.
May 12, 2004, 10:21 AM
#42
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not a new idea
This is probably not a new idea, but what about the oil squirters on the bottom side of the piston? Would clogging one of those allow a heating condition severe enough that the piston has a hard time shedding heat?
Later,
jcnel.
Later,
jcnel.
May 12, 2004, 02:57 PM
#44
My guess is bad gas. Just because you pumped 98 octane, doesn't mean 98 octane was actually in the tank.
Try and see if you can get the gas tested from your fuel tank. If it's not as advertised, perhaps you can get some recourse from the gas station??
Try and see if you can get the gas tested from your fuel tank. If it's not as advertised, perhaps you can get some recourse from the gas station??
May 12, 2004, 03:05 PM
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Did you guys read the 720 degree temps in the Downpipe! Frist off the EGT probe needs to be 3 inches away form the head. So 720 degrees C at the down pipe would have the EGT at the combustion chamber well over 1100 degress C. Think about this once it hits the O2 housing it has a chance to expand and cool down. It cools even more when it hits the downpipe. Why do you think our o2 sensors are heated.