Piston Hole: Causes, Repair & Prevention

Hello everyone,

Last week, my Bora 1.9 PD, engine code AJM, manufactured in July 1999, with 160,000 km (approximately 99,000 miles) and no modifications, experienced a rather dramatic failure. Initially, it started to jerk, then it began to smoke, and finally, it revved itself up uncontrollably. Upon opening the engine, it was discovered that the fourth piston had a crack and a piece of material had broken off.
Question: Could this have been caused by a faulty injector nozzle element, leading to overheating? Wouldn't there be signs of burning or melting in that case?
Or does it look like a material defect?

Best regards,
Stefan

Well, first of all, my condolences. That faintly visible "spray pattern" looks like what I've seen in other direct injection (DI) engines when I've had to look inside. The question is, how does a DI injector fail? They shouldn't be causing drips or leaks from the valve timing. However, you can't completely rule it out. In the past, I've only seen this happen when an injector was completely finished, causing it to shine and become unusable. I've only encountered this twice in my extended circle of acquaintances. The material buildup is located in a spot where a nozzle opening is, so it's possible that the spray was directed onto the piston due to a clogged nozzle opening... just speculation.

Since it's hard to see clearly in the photo, which came first: the tear or the crack across the piston? It's difficult to say for sure based on the self-running process which one is newer.

If you have the PD numbers that end with "F", I still have 2 available, and you can have them for the shipping cost and a case of beer ... I'm currently in the process of selling everything.

Thank you for the offer! I'll check which type is installed.
Thinking about it, I noticed a slightly irregular engine sound weeks beforehand.
It became noticeable when the engine was idling (with a cold engine). It might have been caused by the crack.

Best regards,
Stefan

"Well, it's hard to say for sure... it might be more likely related to issues with the valve train, but of course, it could also still be caused by the faulty piston. It's always difficult to determine the exact cause retrospectively."

Hello.

Based on what can be seen in the pictures, it appears to be a material fracture. This seems to have happened a few times before with the early PD AJM engines.

Have you already checked whether it's still worth having the machine repaired, or could a replacement engine be an option to get the car running again?

Regards,

hb2000

I will get the engine repaired. According to the initial inspection by the workshop, the turbo is...
Order. Since the workshop had not opened the engine and, due to the lack of...
The compression of the aforementioned cylinder, leading to a major engine failure, prompted the following advice:
'...to an AT engine. However, the planned cost of approximately €5200 is too much for me!'
Therefore, I disassembled the car myself (I have good workshop equipment, including a lift).
(Experience in mechanical assembly required.)
I'd like to know if the problem is due to a material defect in the piston or a faulty pressure sensor.
Element was.

Best regards,
Stefan

Have you found the broken piece(s)? No matter where they are, they should have caused some damage... I'm sure of it.

My sincere condolences.

"I saw this damage three months ago on an old 1Z engine that a friend of mine was repairing. The engine had also been driven for less than 200,000 kilometers."

All I can say at the moment is that, according to the engine manufacturer's inspection, the fuel injectors were supposedly in good condition.

It doesn't seem to be a typical problem specific to Pd engines.

No, I haven't looked for the broken piece yet.
A preliminary visual inspection of the head, runners, and valves.
resulted in no visible damage.

Best regards,
Stefan

If you're lucky, the broken piece is in the oil pan... but it could also have been ejected by the loader.

According to the initial workshop inspection, the turbo is...
Order.

'Did the workshop also inspect the exhaust side, or only the intake side and radial clearance of the turbine shaft? A faulty turbine wheel, or a variable turbine geometry (VTG) stuck due to a fragment, might not necessarily be immediately apparent during such an inspection.'

The cylinder head is currently still hanging from the engine crane.
This weekend, I'll take a closer look at everything.
and I'm going to run the drained oil through a filter.
I'll also take another look at the turbo.

Best regards,
Stefan

If the head is removed, checking the turbocharger is never a bad idea, and it's a quick process. If the broken piece can't be found, I would also quickly disassemble the exhaust side; it's very straightforward with Garrett turbos. In my opinion, the small blades inside can't survive being hit by a piece of debris. It would also be interesting to see how that piece, which is quite large, made its way past the valve and all the way to the turbo.

The crumbs could now also be lodged in the oil pump's suction strainer.

Okay, I took a closer look at the cylinder head and rotated the camshaft once.
and I visually inspected each valve. There were no issues found on either the valves or the head.
'Can you see any traces of the fragment?'
I disassembled and cleaned the turbocharger from the exhaust side. Again, there was no trace of it here.
Pieces.
At least, the VTG is now moving smoothly again .
The loading coil has no noticeable play.
I haven't looked in the oil yet, but I don't think it could be in there.
The hole in the piston doesn't have such a direct connection to the oil pan, where the fragment is located.
could have made it through.

Hello,

It doesn't appear to be thermal damage to the piston caused by excessive diesel combustion. I would also check the oil injection system for the piston from below. If something is wrong there, the piston can also overheat (>crack) without necessarily showing signs of melting from the top.

Greetings, Albrecht.

The approach with oil injection sounds plausible.
I once tried using a 50ml syringe and a piece of tubing.
To apply pressure or vacuum to the curved tube. Nothing happens .
No hissing or bubbling - nothing at all. The syringe barely moves.
Am I testing against some kind of pressure relief or check valve?
Ich habe den gleichen Versuch mal bei Zylinder 3 gemacht. With the same...
Result