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Originally posted by egregore:

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For those on this board who are very at home spinning a wrench (I include myself in that group), what do you think the chances are some rather substantial foreign object got into the cylinder causing an impact so severe it resulted in a cracked diesel piston, without also severely damaging the cylinder wall, valves, ports, or head? My bet, pretty damn low.

In a combustion chamber half or a third of the volume of a gas engine? No way.

Volume aside, the only way that piston would be cracked (if you accept the dealership explanation) would be for that 'foreign object' to be trapped between the face of the piston and the head, valve(s), and/or port(s). Short of pulling that head and personally showing me the cylinder walls and valvetrain, I wouldn't for a moment believe there isn't additional damage in there. If the Op has access to a good bore scope, he should run that down inside cylinder #5 and have a look for himself.

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Originally posted by Excam_Man:

Why is it too much trouble for people to be honest and have integrity?

Its a car/truck dealership. Its what they do.

I would pay the $7900 for a brand new engine, wouldn't rebuild this one. I deal with diesels on a daily basis. I have seen some miraculous diesel failures. Pulled turbo's on a 1400 hp CAT 3412 that wasn't making as much power as the other engine (in a yacht) but still running fine, boat would run at cruise speed the same speed etc. Turbo vanes all chewed up......pull heads, several valve seats completely missing. NO damage to the pistols, cylinder walls or anything. On another engine, I did see a valve strike a piston and crack it, it did bend the valve though. You can crack a piston in a diesel with no wall damage sometimes if you hydrolock that one cylinder.......however, most (not all times) you'll bend the connecting rod as well.......Either way, I wouldn't spend the $2k to fix the one cylinder and call it good......I'd replace the entire engine for $7900 (and make sure it comes with a warranty.)

There are a lot of threads on these engines with cracked pistons, if you do a search. "2015 duramax cracked pistons". So it's somewhat common.....Even more reason to put a new motor in it instead of fixing the one hole. Something about the CP4 fuel injection pump shredding itself and sending debris through the engine, and several threads of people retrofitting the earlier cp3 injector pump.

This message has been edited. Last edited by: jimmy123x,

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There are a lot of threads on these engines with cracked pistons, if you do a search. "2015 duramax cracked pistons". So it's somewhat common.....Even more reason to put a new motor in it instead of fixing the one hole. Something about the CP4 fuel injection pump shredding itself and sending debris through the engine, and several threads of people retrofitting the earlier cp3 injector pump

Dad told me about an article he read that was about this. And we think this is the cause.

I think his plan it to get rid of it for a new or newer one.

Pics the damaged piston and the piece of metal they found.

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Pics the damaged piston and the piece of metal they found.

The top pic is actually the combustion chambers and valves in the bottom of the cylinder head. It's unusable - there is severe gouging around the perimeter of the combustion chamber where the head gasket "fire ring" seals. The piston will look much worse, I'm sure.

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Originally posted by egregore:

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Pics the damaged piston and the piece of metal they found.

The top pic is actually the combustion chambers and valves in the bottom of the cylinder head. It's unusable - there is severe gouging around the perimeter of the combustion chamber where the head gasket "fire ring" seals. The piston will look much worse, I'm sure.

Missed including that one. Post has been edited.

I'm no diesel mechanic.....

Where's the metal that they found that caused the damage? Those metal pieces look to be what was gouged out of that piston, and not like what I would expect to cause the damage seen. The cylinder walls do look in pretty good shape. So do the heads and pistons minus the impact damage.

So.....where's the piece that caused the impact damage?

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Originally posted by jimmy123x:
There are a lot of threads on these engines with cracked pistons, if you do a search. "2015 duramax cracked pistons". So it's somewhat common.....Even more reason to put a new motor in it instead of fixing the one hole. Something about the CP4 fuel injection pump shredding itself and sending debris through the engine, and several threads of people retrofitting the earlier cp3 injector pump.

Based on the pictures posted after your post, I don't believe that's what happened here.

One, Walker77's dad's piston is not cracked.
Two, the cracked pistons from a CP4 failure are because tiny bits of metal from the failing pump jam an injector open flooding the cylinder too much diesel. The excess fuel doesn't compress or ignite like normal and the piston cracks.
Three, the chunks of metal in the pictures look too large to have come through the injector.

The question now is where did the metal come from?

SOMETHING got inside the cylinder.

Ingested through the intake, as if there was work done on the intake and somehow foreign object debris was allowed in.

Something small enough to get past the valve would be a lock washer of some sorts.

I've seen it many times on gasoline engines where a small object got dropped into the intake and wrecked the head.

Even using a bolt that is too long on the manifold can punch through it, leaving debris capable of wrecking the head.

There are other possibilities that are easy to eliminate. The tip of the glow plug for example which in this case is clearly intact in the cylinder head photo as are the valves. The tip of the injector or a valve seat are other easily eliminated possibilities.

After that, we come back full circle to the work the dealer did replacing the EGR assembly which opens a clear path to the intake manifold. Truck worked fine before that, and then blew during the test drive after the work was completed.

I would not accept any solution that did not include a new or rebuilt long block with the dealer bearing the full cost. I wouldn’t want the dealer doing the work either.

Looking at the head it appears like the top left valve is cocked a bit the inside looks down in the seat and the outside edge looks up. Compare it to the others which have a different color and that cylinder looks black. Metal may have got under the open valve and bent it or came out of it?

A warranty offered by professional liars is worthless, of course.

I'm trying to understand how the piston head surface looks like a melted lava cake.

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Originally posted by jimmy123x:
There are a lot of threads on these engines with cracked pistons, if you do a search. "2015 duramax cracked pistons". So it's somewhat common.....Even more reason to put a new motor in it instead of fixing the one hole. Something about the CP4 fuel injection pump shredding itself and sending debris through the engine, and several threads of people retrofitting the earlier cp3 injector pump.

Then it should follow that we'd see damage in more than one cylinder since the fuel pump feeds all cylinders. This appears to be a single cylinder damaged.

I guess it's possible the fuel pump tossed off some metal and it went to #5 only, but doubtful. Piston looks damaged but intact,

It's odd that the cylinder walls appear to have zero marks...

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Originally posted by Russ59:
I'm trying to understand how the piston head surface looks like a melted lava cake.

Diesel pistons have a large recess with a raised part in the center, the black is probably carbon built up or camera angle or both.

You need to establish direct contact with someone at GM, not just the dealership.

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Originally posted by Russ59:
I'm trying to understand how the piston head surface looks like a melted lava cake.

One of the valves shows some evidence of impact with whatever was ingested into the cylinder and it also appears that the valve in question 'may' be bent and not seating/sealing properly. This would result in incomplete combustion and unburned diesel fuel on the surface of the head and piston. Further, whatever was ingested into the cylinder was repeatedly being smashed between the piston and the combustion chamber of the head, so they look a little 'beat to shit' as a result!

That 'stealership' would NOT get a nickel from me on this! I would accept nothing less than a replacement engine entirely on their dime. Their tech screwed up big time, and they need to make it right!

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That 'stealership' would NOT get a nickel from me on this! I would accept nothing less than a replacement engine entirely on their dime. Their tech screwed up big time, and they need to make it right!

At this point has anything concrete been proven that the work done is the cause, other than they took it to a dealership and a mechanic changed a part.

Very interested to know where the metal come from, was it the result of something that the mechanic did or was it simply something that failed.

^^^If it was something that 'simply failed' they NEED to produce the part in question. Chunks of metal don't just get into a sealed intake system and ultimately the cylinder/combustion chamber! Just prior to the 'failure' their service tech had replaced the EGR.

As previously posted by 'trapper189' - "Removing the EGR valve opens a path into the center of the intake manifold and cylinder 5 is one of the 4 central cylinders."

Per a previous post by the OP - "I just got off the phone with dad and got some clarification. The (independent) diesel mechanic he talked to said he believes the dealership dropped a bolt in the cylinder when taking off that def valve. Said he had seen it before."

If they want $7900.00 they NEED to produce the failed part, period!

Something got into that cylinder and went for a ride, smashing the shit out of the piston, valves, and cylinder head. What that object was / is, is anyone's guess. The tech who did the work knows exactly what happened. I'm sure when he started it after his initial repair his stomach dropped to his ankles. The foreign object looks too large to have gone through the fuel stream.

I would not pay a single dime to these people, and get every single person that you can think of at GM involved.

Edit to add, I dropped a washer down an intake on a Chevy 350 in high school while rebuilding a carb. When we tore the engine down, it looked just like yours.

Why do you guys think they opened that motor up prior to the OP and his mechanic showing up per their agreement?

They found the cause, and that cause found its way into the nearest trash can before anybody else could see it.