Cracked Cylinder Head Tdi

Hello,
beabsichtige ja den Tausch des Zylinderkopfes bei meinem Tdi! AFN

I've received an offer for a replacement cylinder head and noticed that it has hairline cracks extending towards the valves on all of the injector ports! What do you think, should I avoid it, or can it be installed without any worries? The cracks are small, but almost 0.5cm long.

I also have a defective cylinder head (the crankshaft bolt has come loose), with 2 lifters that have worn out and need to be replaced. However, this head is crack-free and could be rebuilt!

What do you think is better?

Hello Boro,

Neither option is ideal, and it's almost impossible for me to give you advice on which solution is the safer one.

I would definitely not use the cylinder head with these cracks. While VW claims that cracks are normal and can be driven with, the depth is crucial, and 5mm is quite a lot. The next question is, why did these cracks occur? In my AFN, I've only had one cylinder head, and that was for the entire 230,000 km with at least 6 head gaskets. I briefly experienced exhaust temperatures of 950 degrees. Unfortunately, I couldn't measure the pressure in the combustion chamber, but the peak pressures were certainly well over 200 bar, and my head only had a slight crack on one injector. I've always treated it well, letting it warm up properly and allowing it to idle after driving. I've handled many cylinder heads before, and often, although this is not a guarantee, when a cylinder head has cracks like these, something else is usually also not right. Sometimes a valve sticks, a hydraulic lifter fails, or an exhaust swirl valve gets stuck. These are signs that the cylinder head has warped. Any repair would likely be more expensive and time-consuming than replacing the cylinder head.The same applies to your other head.

If I were you, I would disassemble the "defective" cylinder head, checking for cracks, and see if everything is still largely within tolerance. For example, do the valves stick when you try to remove them? Do the hydraulic lifters slide into their bores without needing to be pressed firmly in? Can the injectors/glow plugs be easily removed?
If one or more valves have excessive clearance, it may be sufficient to replace the valve guides. In any case, the valves will need to be re-ground.

If all of that is in place, I would carefully examine the storage area and possibly have it inspected for cracks. If nothing unusual turns up here, it already looks quite good. But that doesn't mean it's a 100% safe situation.

It might be possible, although VW does not recommend it, to have the cylinder head machined flat by a small amount, perhaps a tenth of a millimeter. There are companies that offer this service. This would also ensure a tight seal between the cylinder head and the engine block.

Wahrscheinlich fehlt mir das Vorwissen, aber warum möchtest Du den Zylinderkopf tauschen? What's broken?

Best regards,
Thomas.