Cylinder Head Bolts: Tighten or Replace (Preventively)

Dear DIY enthusiasts,

It appears that there is growing evidence suggesting that the cylinder head bolts (stretch bolts) may not be providing the proper clamping force over time (for whatever reason). Details regarding this can be found, for example, at:

/viewtopic.php?t=8172&highlight=meyert

The exact reason for this is not yet definitively clear. However, based on my experience, I can confirm that the loosening moment of the cylinder head bolts is very small in the case of a cylinder head gasket defect.

Since my Passat, with 240,000 km on the odometer, is also a potential candidate for a gradual loss of coolant due to the cylinder head gasket, and therefore possibly a malfunctioning head gasket, I've decided to try tightening it as described in the article I cited. However, I still have some questions about the process.

To the best of my knowledge, the most common problem with metal cylinder head gaskets is gas leakage from the combustion chamber (high pressure) into the coolant. If it's true that only loose cylinder head bolts cause the reinforced metal ring of the cylinder head gasket (without a silicone layer?) around the combustion chamber to become permeable, then tightening the bolts should actually eliminate the problem, unless there are channel-like damage in that area. Since the cylinder head gasket is made entirely of metal, it cannot deform or "settle."

My idea is to remove the cylinder head cover and first check the screws according to the specified torque sequence (i.e., from the inside out) at 40 Nm and then at 60 Nm. If any screws start to spin at that point, the problem is clear.

Since the suit requirement also includes two 90° rotations, it is now difficult to verify whether this additional requirement is being met. The question is: How can I check this additional rotation angle? Since further testing with higher torques (e.g., 80 Nm, then 100 Nm) is not useful for stretch bolts, only loosening the screws and re-tightening them according to the specification makes sense , with the hope that this will not cause any leaks in the cylinder head gasket (ideally, work with a vacuum in the cooling system). The question is: When loosening the first screw, should you follow the REMOVAL INSTRUCTIONS (i.e., the sequence from outside to inside) or the INSTALLATION INSTRUCTIONS (i.e., the sequence from inside to outside)?

My idea is to loosen each screw completely one by one, and then tighten them to 40 Nm. After this first step, the second tightening should be done to 60 Nm, and finally, both steps should be repeated with a 90° angle each time. Should the old screws be reused, or should they be replaced for safety's sake (the article mentions that re-tightening the old screws 2-3 times is acceptable)?

What do you think of this idea? Thank you in advance.

gäääähhhn.....another homeopathic screw-up .

Here's the translation:

"The fact is: if the gasket allows even a minimal amount of exhaust gas to leak, then adjusting the timing (120-150 Nm, more or less, depending on feel) *can* postpone the need to replace the head gasket (I've done it myself)."
Normally, the screws connecting the 1/2" T-piece and extension (pipe) should only be loosened with a corresponding amount of force if they have been tightened correctly. I wouldn't recommend tightening them further, as this could potentially damage the gasket, especially if the seal is already weak, and you're increasing the pressure unevenly (according to the tightening specifications).

Wait until it has completely cooled down, and then replace the seal .

Hello everyone!

I completely agree with what vwSchrauBär said.

I would strongly advise against making any unspecified changes to the torque of the cylinder head bolts.
As often stated, ZK screws are only to be used once! Anyone who insists on doing it differently should not be surprised if something goes wrong;-).
Furthermore, repeatedly loosening and tightening the clamping screws can lead to an unacceptable imbalance of forces between the clamping device and the workpiece. It is also clear that this process exposes the clamping device to internal stresses, and that it is already prone to cracking.
It's not for nothing that both the sequence and the timing of tightening the bolts must be followed - not because an engineer thought that a 180° tightening angle was too boring for a train...

As my grandpa used to always say: "If it ain't broke, don't fix it!!!"

Best regards from Munich!

Tightening it further? Not for these parts. Especially not after 240,000 km, at that point the seal is likely only good for one thing: replacement. Metal gaskets can't be compressed, and if the cylinder head has been worked on anywhere near the seal, the sealant is damaged, making the head gasket a candidate for replacement. It's important that the expansion bolt has the correct spring force. However, these expansion bolts also wear out over time. Tightening it even more just stretches the bolt and reduces its tension.
Everything needs to be renewed.

Hello,

If possible, I would replace the cylinder head gasket bolts. Replace them one at a time and tighten them to the specified torque in stages. This way, you'll have an old gasket, new bolts, and the correct tightening torques.

Best regards.
Christian.

chris11 wrote:

Hello, If possible, I would replace the cylinder head gasket bolts. Replace them one by one and tighten them individually according to the specified torque. That way, you'll have an old gasket, new bolts, and current tightening torques. Best regards. Christian

What's the point? If the old head gasket still leaks even with new screws, it's a waste to throw away the new screws when you replace the head gasket. The screws are only meant to be used once! See the post by RedR32!
The best solution, and it remains the best, is a new cylinder head gasket and new bolts. That way, you'll have peace of mind for a long time!

That's true. Except for engines with "motorsport tuning" (meaning a 50+% increase in power), the gasket is usually the weak point. Unless the cylinder head is warped, which is a common problem with the 1.9 PD engines. You can tell this is happening because cylinders 3 and 4 are leaking into the coolant.