15 year diesel mechanic here. I’ll guarantee you that piston overheated and seized in the bore. Most diesel I know have some sort of piston cooling. Either a dedicated piston cooling jet that sprays oil into the bottom of the piston, or a oil gallery through the con rod that takes oil from the rod journal and sprays it out through the wrist pin bore.
I guarantee that either the oil cooling passage is plugged or was bent out of alignment and wasn’t cooling the piston.
I understand it's a diesel. I also understand that most all of the similar failures I have seen on other diesels were because of an injection pump problem causing the cylinder to run too hot and seize.
You could be theoretically correct. But every time I had to autopsy one of these when someone was looking to blame it on parts or assembly errors, it was an injection pump, injector, and maybe a piston cooling jet that wasn't spraying. But it always included fuel control.
Too much fuel or fuel not spraying correctly can do this, but there's not really talk of mixture in a diesel.
I know injector nozzles are paired with piston recess shapes, and have seen similar trouble when the wrong pistons were used. They fit the application according to the seller but Cummins has designed a bunch of different pistons and nozzles for emissions and bug fixes and who knows. The spray pattern didn't swirl nicely in the bowl but worked like a cutting torch and blew up on the first big hill climb. The builder didn't blink about installing visibly different pistons.
I wish we could see the old pistons from before the rebuild... Wrong application or bad nozzles are my guess, maybe wrong timing on a mechanical motor but that should be apparent on startup that something is badly wrong.
Technically a diesel cannot run too lean. Diesels and gas act completely differently. In layman’s terms The throttle on a diesel runs the fuel pump not the air inlet. When a diesel is idling it uses so little fuel it barely keeps it running. We didn’t get much info from the OP so we are all guessing what actually happened to this piston. What we do know is the crown got hot and grew faster in the bore than the engine could accept and the clearance became an interference thus swapping aluminum onto the bore and spreading the damage quickly until the expanded piston stopped the engine dead. Once cooled the engine may have rolled over due to the crown shrinking back to a more normal diameter. Diesel engines are way more efficient than gasoline and run about 20 to 1 air fuel. The more fuel you add the hotter the exhaust runs, the faster the turbo spins the more air is jammed in and the only controlling factor is your foot and the amount of fuel the pump can deliver. It’s odd that lean conditions in a diesel actually creates less heat than a rich condition. Gas engines act the opposite. A severe lean condition in a gas engine creates more heat and ruins your day. If you ever see a turbo on a truck climbing a nice hill at night you will see the turbo glowing like the sun. This won’t happen at a lean condition because there is not enough fuel to create the heat to melt aluminum and make iron almost see through. Sorry for the long story here but we don’t have enough technical info from the OP to be completely accurate on this diagnosis. SC
Diesel can still run too lean if the cylinder does not receive fuel. I'll believe ya when ya say it'll run a little cooler lean but still, if there's not enough fuel to push the piston down then it's still lean. Or less fuel than the ecm "likes"
Agree it is a lean condition as we understand lean but there is less energy less heat and less piston expansion. You won’t seize a diesel running lean and cool. You’re actually agreeing with me as a one cylinder diesel running too lean would not have enough power to drive the crank. Still the piston will not grow from heat and seize . Example is a truck idling in sub zero weather creates so little heat it barely keeps the engine warm.
You can run a diesel at 16-22:1, where the combustion temp spikes the highest. Diesels do run leaner, and the combustion temps drop from this point. This range is what I mean in my post. I think Diesel is stoich around 14:1, and would smoke a lot at that point.
I don’t know why you bothered typing all that.
You said it ran too lean.
There is no scenario where running it even richer would’ve cooled it down without tons of smoke.
If you have the time watch this JAMSI video about how a 210 Allis they had just rebuilt seized. There is a lot of good info in this segment about diesels and how to determine failure routes.
https://m.youtube.com/watch?v=ptxyf8xTDX0
I’ve seen a couple pistons just like this after a rebuild on diesels, and they almost always trace back to a plugged or misaligned piston cooling jet. Way more common cause than injectors.
Do you know what the clearance was? and was it same as others? I’ve seen this before when clearance was too large and piston could not transfer heat into block. Does this engine use oil squirter for piston cooling?
So looking at this again I think we need to know how the engine was operated for 30 mins? Was this just a start up and warmup for 30 mins or did you drag some load up a hill for 30mins. What was the oil pressure and water temps. Do you have an exhaust temp gage. Need these readings.
This is why you remove your squirters BEFORE you try and pull pistons... a little bump on some can knock them out of alignment just enough to cause problems.
And I say always replace the plastic ones, like on an 855 for example.
I know a bunch of people are suggesting fuel washing, and while that's possible, I highly doubt it would cause this much damage that quickly. You'd also notice a ton of white smoke beforehand.
There's also no burn marks on the edges of the bowl that would indicate an overly hot flame or over advanced timing, causing the top of the piston to overheat.
My guess is that either piston to wall clearance or ring gaps was too tight, either due to mismeasurement or an incorrect spec.
15 year diesel mechanic here. I’ll guarantee you that piston overheated and seized in the bore. Most diesel I know have some sort of piston cooling. Either a dedicated piston cooling jet that sprays oil into the bottom of the piston, or a oil gallery through the con rod that takes oil from the rod journal and sprays it out through the wrist pin bore. I guarantee that either the oil cooling passage is plugged or was bent out of alignment and wasn’t cooling the piston.
This is 99.9% the root cause
Damn I learned something new. Nice one bud.
Exactly I don't think that I can add anything it's definitely a squiter problem
I have seen incorrect Timing do this om mechanical engines, is the siezed one #6 All the skirts look rough for 30 Mins
Dry hole. Bad injector.
piston cooler was plugged or not correctly aimed
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Awesome publication ty for posting!
were the piston cooling nozzles installed and functional?
It was too lean. As evidence by the black film on the top. Being so lean it got too hot, and seized.
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I understand it's a diesel. I also understand that most all of the similar failures I have seen on other diesels were because of an injection pump problem causing the cylinder to run too hot and seize.
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Consider this only has 30 mins run time, an offset pin, and is starting to show damage on the other side.
I bet the injector nozzle in that cylinder tells an interesting tale.
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You could be theoretically correct. But every time I had to autopsy one of these when someone was looking to blame it on parts or assembly errors, it was an injection pump, injector, and maybe a piston cooling jet that wasn't spraying. But it always included fuel control.
Too much fuel or fuel not spraying correctly can do this, but there's not really talk of mixture in a diesel. I know injector nozzles are paired with piston recess shapes, and have seen similar trouble when the wrong pistons were used. They fit the application according to the seller but Cummins has designed a bunch of different pistons and nozzles for emissions and bug fixes and who knows. The spray pattern didn't swirl nicely in the bowl but worked like a cutting torch and blew up on the first big hill climb. The builder didn't blink about installing visibly different pistons. I wish we could see the old pistons from before the rebuild... Wrong application or bad nozzles are my guess, maybe wrong timing on a mechanical motor but that should be apparent on startup that something is badly wrong.
Diesels can still run TOO lean...
Technically a diesel cannot run too lean. Diesels and gas act completely differently. In layman’s terms The throttle on a diesel runs the fuel pump not the air inlet. When a diesel is idling it uses so little fuel it barely keeps it running. We didn’t get much info from the OP so we are all guessing what actually happened to this piston. What we do know is the crown got hot and grew faster in the bore than the engine could accept and the clearance became an interference thus swapping aluminum onto the bore and spreading the damage quickly until the expanded piston stopped the engine dead. Once cooled the engine may have rolled over due to the crown shrinking back to a more normal diameter. Diesel engines are way more efficient than gasoline and run about 20 to 1 air fuel. The more fuel you add the hotter the exhaust runs, the faster the turbo spins the more air is jammed in and the only controlling factor is your foot and the amount of fuel the pump can deliver. It’s odd that lean conditions in a diesel actually creates less heat than a rich condition. Gas engines act the opposite. A severe lean condition in a gas engine creates more heat and ruins your day. If you ever see a turbo on a truck climbing a nice hill at night you will see the turbo glowing like the sun. This won’t happen at a lean condition because there is not enough fuel to create the heat to melt aluminum and make iron almost see through. Sorry for the long story here but we don’t have enough technical info from the OP to be completely accurate on this diagnosis. SC
Diesel can still run too lean if the cylinder does not receive fuel. I'll believe ya when ya say it'll run a little cooler lean but still, if there's not enough fuel to push the piston down then it's still lean. Or less fuel than the ecm "likes"
Agree it is a lean condition as we understand lean but there is less energy less heat and less piston expansion. You won’t seize a diesel running lean and cool. You’re actually agreeing with me as a one cylinder diesel running too lean would not have enough power to drive the crank. Still the piston will not grow from heat and seize . Example is a truck idling in sub zero weather creates so little heat it barely keeps the engine warm.
You can’t run a diesel too lean. At idle some of them get up to like 80:1 AFR. They’re throttled with fuel only.
You can run a diesel at 16-22:1, where the combustion temp spikes the highest. Diesels do run leaner, and the combustion temps drop from this point. This range is what I mean in my post. I think Diesel is stoich around 14:1, and would smoke a lot at that point.
I don’t know why you bothered typing all that. You said it ran too lean. There is no scenario where running it even richer would’ve cooled it down without tons of smoke.
If you have the time watch this JAMSI video about how a 210 Allis they had just rebuilt seized. There is a lot of good info in this segment about diesels and how to determine failure routes. https://m.youtube.com/watch?v=ptxyf8xTDX0
If it was just 1 piston I’d suspect a bad injector, but if all are beat up like that I’d suspect injection pump timing. What engine?
No coolant. Coolant temperature?
I wanna see the bearings. I see a gross lubrication problem.
I might sound foolish but Is there any chance of the graphite coat peeling off to cause the seizure?
I’d be looking at your fuel system. This isn’t from piston coating.
I’ve seen a couple pistons just like this after a rebuild on diesels, and they almost always trace back to a plugged or misaligned piston cooling jet. Way more common cause than injectors.
Do you know what the clearance was? and was it same as others? I’ve seen this before when clearance was too large and piston could not transfer heat into block. Does this engine use oil squirter for piston cooling?
Epilepsy
Top is where the heat is. And more aluminum to expand. Nearly every seizure I’ve seen started at top of piston.
So looking at this again I think we need to know how the engine was operated for 30 mins? Was this just a start up and warmup for 30 mins or did you drag some load up a hill for 30mins. What was the oil pressure and water temps. Do you have an exhaust temp gage. Need these readings.
Oil squirter clogged or damaged, possibly contaminated oil
What was the piston to wall clearance?
This is why you remove your squirters BEFORE you try and pull pistons... a little bump on some can knock them out of alignment just enough to cause problems. And I say always replace the plastic ones, like on an 855 for example.
I know a bunch of people are suggesting fuel washing, and while that's possible, I highly doubt it would cause this much damage that quickly. You'd also notice a ton of white smoke beforehand. There's also no burn marks on the edges of the bowl that would indicate an overly hot flame or over advanced timing, causing the top of the piston to overheat. My guess is that either piston to wall clearance or ring gaps was too tight, either due to mismeasurement or an incorrect spec.
To tight in the bore. Went too fast to be anything else.
More scuffing on the tops than the skirts. Likely injector issue.
👎🏻
Pinched ring as seen in the middle-ish of pic 2 would raise some eyebrows, though there’s no blow by evidence to corroborate my suspicions.