Cylinder Head Boring: Guide & Best Practices

Hello everyone,

I'm experiencing a problem with an Audi 8K with a 3.0 TDI engine (CCWA code) where cylinder 2 has a leak in the exhaust manifold gasket.
Make sure to thoroughly coat the supercharger intake pipe with oil-soaked rags.
Also neue Krümmerdichtung eingebaut, alles sauber mit Drehmoment angezogen. Wonderful work.
We were surprised that the engine actually looked quite good, considering the amount of exhaust it was producing.
Engine start... Absolutely the same problem. It immediately starts leaking again from the same spot (which is just great).
So, everything's taken apart again.
Now, next to the stud, there's a hole (see pictures) that was completely filled with exhaust sludge and goes about 6.5cm into the cylinder head.

Does anyone know what this hole is for?

Because I suspect that the leak is coming from here.
I would now clean the hole and either plug it with a set screw or glue in a 5.5 mm stainless steel pin.
This hole is also cleanly recessed to accommodate the exhaust manifold gasket.
Therefore, I also suspected that the exhaust manifold gasket was defective. It's likely that the cylinder head is cracked somewhere, either near the exhaust port or the combustion chamber.

Has anyone ever experienced this issue before?

Oh yeah. The exhaust manifold is only "slightly" warped.
According to the feeler gauge, it's approximately 0.05mm. That should be enough clearance for the seal to move freely.

Hi,

Yes, I'm familiar with that. I've already been through it.
The drillings (yes, each cylinder has one) must not be blocked under any circumstances; these are the "relief holes" for the injectors and are important .
Each injector has 2 seals.
- place the O-ring facing upwards, towards the valve mechanism.
- a copper ring facing the combustion chamber.

The copper ring is 99% burned through. This allows exhaust gases to bypass the injector. If the hole weren't there, the overpressure would be released towards the valve cover and enter the engine. It could also allow oil to enter the combustion chamber, which is why the designer created the hole.

However, both rings and the small O-ring for the oil leak line at the top of the injector must always be replaced.
Recommendation: Replace everything; only one was leaking, and four others were close to it. You could have saved yourself the cost of the exhaust manifold gaskets .

Images:
- View from above into the injector shaft.
- the four worst of the copper rings.
- cleaned injector with new O-ring.

Regards,
Mpire

@Mpire is correct; if it's coming from this hole, then the copper ring on the injector is leaking.

Knowledge is power.
Ignorance is bliss.

Thank you for your responses.

I will remove the injectors on Monday and enjoy the assembly of the manifold.

I'll get back to you on Monday.

Regards,
Bolzer.

Hello,

Thanks to Mpire for the information about the drilling! I wasn't aware that they end there.

I've already had customer vehicles where the fuel injectors seized because they weren't sealing properly against the cylinder head in the combustion chamber area. So, exactly the described case.

The exhaust gases flowing past then caused these components to overheat, which could prevent the affected nozzle from opening or closing properly. The nozzles/pistons and the seat of the injector/nozzle in the cylinder head can be damaged, so it's best to avoid delaying the repair if possible.
Knocking sounds while driving: Injector is stuck, do not continue driving.

Always use new copper rings and clean the seat in the ZK (spark plug ignition coil). Be careful, as cotton swabs can fall into the combustion chamber.

Best regards, Rainer.

dieselschrauber wrote:

Always use new copper rings and clean the seat in the ZK (spark plug housing). Be careful, as cotton swabs can fall into the combustion chamber. Best regards, Rainer

Right, don't use any excessively small scraps of material or anything like that, because the shafts feel very deep. You can't reach the bottom with any pointed tweezers or pliers.

You can laugh at me, but I always use regular O.B. tampons .

Advantage:
They already have a string attached to them. You insert the string, then saturate the object with WD-40 or brake cleaner. When they swell up, they pull out all the dirt with them.
You can also insert a large, long tool into the opening (OB), apply pressure, and rotate it to clean the sealing surface at the bottom of the shaft.
OB plugs are also suitable for sealing the oil and return holes in the engine block when cleaning or removing the head gasket surface.

Okay, and now let's stop (with) laughing .

Regards,
Mpire

Thanks for the tip about the OBs, I'll have to try that next time.

Hello everyone.

Your diagnosis was absolutely correct.
The injector was leaking.
Everything is covered in grime.
Cleaning the shaft with an OB (presumably referring to a specific tool or method) works really well.
Very good idea.

Thank you again for your help.

Regards, Bolzer.