1.9 TDI Turbo: Keeps Failing, Replacement Issues

Hello,
The following problem:
1.9 TDI engine, common rail injection system (engine code AVQ), with approximately 280,000 km on the clock.
He received a new (brand new, still in original packaging) Garett 751851-5004S turbocharger (including new oil feed and return lines, a new catalytic converter, and exhaust system). The oil pressure was checked and was fine. However, after only a few hundred kilometers, it became noticeable due to hissing noises. Upon removal, it was found that the exhaust manifold was warped. The turbocharger was returned and replaced with a new one.
The engine, specifically in the area around the cylinder head gasket (Gasket), was quite oily, and I had to regularly top up the oil. Initially, it wasn't clear where the oil was coming from. The workshop (a VW dealership) suspected that the cylinder head gasket might be faulty, as the valve cover was new and its gasket was dry all around. The head gasket had been replaced about six months prior. The cylinder head was removed, and during the process, a warped exhaust manifold was discovered (cylinders 1 and 4). It was also noticeable that oil was leaking from the exhaust manifold gasket.
The question now is why the exhaust manifold is warped again (it was always replaced with a new gasket, new nuts, and tightened to the correct torque).
"The valves were removed and the valve guides were inspected; they are in excellent condition. The valve stem seals were replaced. It is noticeable that the intake valves are oil-caked, while the exhaust valves are dry. There are also visible light deposits on the pistons (see pictures), although I have not experienced any coolant loss. The injector pump elements are also quite caked (these were replaced with new, non-remanufactured parts about six months ago)."

He has generally had good performance, and there have been no errors in the diagnosis.

The question is, why does the exhaust manifold keep warping? It can probably only happen because it's getting too hot. Why is there so much oil on the intake side?

I recently checked the compression (but the current fault pattern was already present), and it was absolutely excellent (3 readings of 31 bar and 1 reading of 33 bar).

All the cylinders look good. Should the piston rings be checked/replaced?

Hello.

Quote:

The question now is, why does the exhaust manifold keep warping?

It can probably only happen because it's getting too hot. }
Is that correct? Is the tuning strange, or does the car also produce a lot of smoke normally?

Best regards, Rainer.

No, he doesn't smoke, and he doesn't modify his car.
"Nothing was changed. It used to have a Borg Warner turbocharger, now it has a Garrett one. But that shouldn't make a difference."

Do you have any idea what those white deposits might be?

The engine was completely disassembled again, but without any further findings that would lead me to say, "This is it."
The pistons have been removed and will be fitted with new rings; the connecting rod bearings look good. Which manufacturer would you recommend for the rings? The pistons are Mahle.
However, we found a part in the oil pan that we can't identify. It looks like it might be from a needle bearing, but no one knows where it came from. Does anyone have any ideas?

Briefly:
New Mahle piston rings were installed, valve stem seals were replaced, pump nozzle elements were cleaned and tested on a Bosch dynamometer, a new cylinder head gasket was installed, a new turbocharger was fitted, and everything was assembled.

Let's see how it performs. After 1000 km, I'll change the oil again to remove any potential wear particles from the new parts.

Hi!

It's not uncommon for exhaust manifolds to warp.
I don't know why, but I've seen quite a bit of that. I've experienced it with highway maintenance vehicles powered by diesel engines, and also with the elderly woman who drives a small gasoline-powered Polo, and who only uses it occasionally to drive around the village and go shopping.
Sometimes, forces act that can pull the threaded bolts out of the cylinder head.
I'm generally not a fan of torque wrenches for things like that, because you mentioned it.
I rely more on my intuition and experience to determine how stable and secure the mother feels.

There's also this unspoken rule that once a piece of pastry has crumbled, it tends to stay that way.

I often had those spoiled exhaust manifolds professionally milled flat in a mechanical workshop. This always solved the problem, and some of those cars are still on the road today.