AJM & ZKD Issues: Troubleshooting Guide

Hello fellow mechanics.

I've now experienced problems with my AJM engine for 50,000 km, including coolant loss and bubbling in the heat exchanger, which is also causing weak heating performance.
A week ago, I had a colleague, who is a great mechanic, replace the ZKD (cylinder head gasket), and since then, everything has been running smoothly. The cost was €495.

The following changes have occurred in my Passat after replacing the head gasket:

1. The pressure in the cooling system is back to normal - there's hardly any hissing when opening the cap.
2. No further water loss detected in the cooling system.
3. The annoying gurgling sound in the heat exchanger is gone.
4. The heating system gets as hot as a Finnish sauna.
5. During the ride, there is no more jolting or shaking.
6. The idling state is also no longer characterized by vibrations.

The following actions were performed during the head gasket repair:

1. Disassembly of the front section is required to access the timing belt.
2. Expose the head and remove all the surrounding components.
3. Disconnect the head with the integrated PD elements from the block.
4. Head: Flattened the top surface by 1/10 millimeter due to slight warping.
5. Use new cylinder head gasket and new cylinder head bolts.
6. Put everything back together and hope for the best.

The cooling system was thoroughly flushed and then refilled with G12 coolant and water.
As a precaution, an oil change should be performed using a suitable PD oil.

At the ZKD (cylinder head gasket), I was able to identify the damage relatively well. The third cylinder had a damaged area, and exhaust gases from the combustion chamber were leaking into the cooling system.
The exhaust gases found their way out, not from the top of the cylinder head, but from the bottom of the engine block. I probably drove for over 50,000 kilometers with this problem.

Regards,

hb2000

Quote:

4. Head: Flatten the top surface by 1/10 millimeter because there was some warping.

"The 'How-to' guide states that the diesel cylinder head should not be reconditioned - of course, without providing any explanation. How does that even make sense?"

Bye.
peace

Quote:

A week ago, I had a colleague, who is a great mechanic, replace the ZKD (cylinder head gasket), and since then, everything has been quiet. The cost was €495.

It's great that it's working again, and that no further damage occurred after 50,000 km.

You could have experienced this feeling of success much earlier.

Hello.

The 'How-to' guide states that the diesel cylinder head should not be reconditioned.

An experienced engine technician has guaranteed that a value of 1/10mm is not critical.

It's great that it's running again now, and that no consequential damage occurred after 50,000 km.

The risk that it might not be the ZKD (a specific term, likely an abbreviation) led me to this slight delay...

Regards,

hb2000

I once heard something about using a thicker head gasket when having a diesel cylinder head machined, so I knew about the machining process, but I'm not really convinced about the head gasket thing.

Quote:

The risk that it might not be the ZKD [likely referring to a specific component or system] led me to this slight delay...

Sometimes, people just don't want to accept things as they are, even when all the evidence points in that direction.

Sometimes, people just don't want to accept things the way they are, even when all the evidence points in that direction.

It's always also a financial matter, but it was worth it .

If the cylinder head is machined down by 0.1 mm, the compression will increase. This can lead to problems in highly tuned engines. The distance between the open valve and the piston also decreases by 0.1 mm. Theoretically, worn bearings, combined with a machined cylinder head, could create a situation where "unfavorable tolerances coincide" (as VAG puts it), causing the valve and piston to come into contact.

Personally, I would also do it that way and reassemble it in the same manner. In the worst case, it might start to rattle after many thousands of kilometers, but until then, it will run well .

Quote:

If you adjust the head by 1/10mm, the compression will be higher.

However, this difference is minimal, mainly because the cylinder head itself already lacks any combustion chambers that would be reduced by the grinding process. The only reason the compression ratio increases slightly is due to the valve faces, which protrude further into the engine due to the precision grinding. This increase is negligible, only about 1/10 mm, and I don't think the valves would experience any interference at that amount, especially considering how much the camshaft can be shifted relative to the crankshaft before contact occurs.

The valve clearance to the piston at top dead center (TDC) and at valve overlap can be checked by manually pushing the valve open to the appropriate position using a suitable tool.

In this context, it's more interesting to consider that the nozzles of the PD elements are moving even closer to the piston bowl. In an extreme case, this could cause the piston bottom to be hit and, over time, melt or break. The question is whether 1/10 mm is enough.

It's also unlikely, because if you were to rotate a PDE or ESD even by a fraction of a degree during replacement, you would already be experiencing melting damage.

1/10mm can be considered insignificant if everything else is still perfect.

The compression is increasing only negligibly, and the valves are still quite a distance away.

ZKD view from the head side

http://www.heikobaier.de/passat/ZKD_oben.JPG

ZKD view from the hull side

http://www.heikobaier.de/passat/ZKD_unten.JPG

ZKD View Cylinder

http://www.heikobaier.de/passat/ZKD_Zyl.JPG

ZKD View Detail

http://www.heikobaier.de/passat/ZKD_Det.JPG