1.9 TDI Timing Belt: Should You Replace the KW Nut?

Given that the issue of premature wear and surface damage has been observed in some 1Z models due to incorrect strength classes of the connecting rod bolt, and that this problem occasionally occurs in AFN and AHF engines as well, I wanted to ask what your opinion is on whether the connecting rod bolt should be replaced periodically, especially for vehicles with higher mileage exceeding 200,000 km.

Generally speaking, the screw shouldn't come loose, but we've seen horses vomit here before...

Following a specified torque value and tightening angle, along with the presence of appropriate thread locking measures, makes the practice of "torque-to-yield" seemingly unnecessary.

Would you replace the pulley as well, if you noticed that a screw was loose?

I'm actually thinking about checking the condition of my timing belt at my next scheduled replacement, given that I have 355,000 km on it.

Hi,

Quote:

In principle, the screw should not come loose

.
Shouldn't the injection timing for a diesel engine, the ignition timing for a gasoline engine, and the crankshaft/camshaft phasing (OT point) need to be adjusted as well when dealing with a loose bolt?
Well, with vehicles that are 8 years old or older, the crankshaft oil seal is definitely likely to be leaking . The screw has to be removed anyway.

Well, there's a groove that prevents the pulley from rotating even a few degrees; otherwise, the crank mechanism would be completely ruined.

Diesel engines often exhibit issues with cold starting and other performance problems, as evidenced by numerous reports available online.

Deus Violentia wrote:

Well, there's a groove that prevents the pulley from rotating even a few degrees; otherwise, the crank mechanism would immediately be ruined. Diesel engines, for example, show noticeable differences in cold starting behavior, etc., and there are many reports about this here.

If the connection becomes loose and there is more play in the fit, the spline will shear off the crankshaft pulley. It's probably not possible to correctly identify this issue based on the timing marks alone.
I once had a 1.8L 16v gasoline engine, and it had problems with starting and inconsistent power delivery. Sometimes it was great, other times it was terrible. I didn't know what to do. At the VW workshop, they checked the ignition timing, which kept changing after short bursts of acceleration. We were puzzled. But no one suspected a loose crankshaft pulley. After readjusting everything, I was sent for a test drive, and then it happened on the way back: *clunk*, engine off. The conclusion was that the intake valves of two cylinders were bent, resulting in no compression. It turned out that the previous owner hadn't replaced the KW (Krankenwelle - crankshaft) bolt when changing the seal, and probably also tightened it too loosely. That's when I realized what had happened.

Okay, great, it's exactly because of people like that who can't think outside the box that one has to (should have) concerns about such things. But as I said: in my opinion, nothing should happen regardless of mileage, as long as everyone involved leaves the "screw" alone...

However, I'm still interested in your opinion, especially regarding a proactive replacement of the screw as part of the ZR (rotor) change.

How does one actually defend effectively?

Sure, here is the translation of the text from German to English:

"Hi,"
"With the 1Z motor, there is definitely no groove, but rather a chamfer. Grooves led to cracking due to stress concentrations. The subsequent motors should not be different. Therefore, if a screw starts to loosen, everything should be adjusted quickly in the control system."
Sure, here is the translation of the text from German to English:

"vg" translates to "very good" in English.
Herbert.

Quote:

In my opinion, nothing should happen there regardless of mileage, as long as everyone involved leaves the screw alone.

That's how it should be.
With your LL (presumably referring to a lawnmower), there should already be a stream of water running out and completely soaking the belt, right?

Belts dry, oil consumption not detectable .

As long as she can stay, it's best to just let her be.

We've had some that were already at 2xx,xxx km and only came loose with extreme force. I was even afraid the crankshaft would break. In theory, nothing should loosen on its own there.

Just try tightening it to around 120-150 Nm. If nothing moves, then it's stuck.

"Yes, yes, I don't have a problem with tightening things, but as far as I know, there's Loctite in the threads, and if I'm unsure, I might break it off, so no more thread locker then, which just increases the chance of loosening... If I noticed that a screw was loose, I would get anxious and look at the contact surfaces before even thinking about tightening a new screw."

As a tip for removing stuck screws, it is suggested: If you want to remove a large-diameter screw that simply won't budge, it often helps to first turn it a few degrees to the right to break the thread locker. Usually, this makes the process much easier. (Provided that this is compatible with the torque and thread pitch... ).

"There shouldn't be a thread locker there, or is it different with the AHF compared to the 1Z (90 Nm + 90°, unlubricated)? The use of Loctite may change the friction coefficient and thus the preload."
hg
Herbert.

If something moves or shifts when you're "tightening," then you definitely need to do something about it. Normally (i.e., if the screw is tight), it shouldn't move at all within a range of 120 - 150 Nm .

Thread lockers like Loctite are not true thread lockers! They only provide a false sense of security. They rely solely on the tightening torque of the screw, which has fine threads. This ensures a secure tightening torque. However, as corrosion increases, the tightening torque decreases, and the connection begins to loosen. Therefore: Never tamper with a running system! Only check if the screw is tight.

Quote:

Screw lockings like Loctite are not actually screw lockings!

This only provides a false sense of security.

These types of screw lock washers essentially only serve to prevent a loosened screw from turning out completely. However, with the crankshaft bolt, it doesn't really matter – once it's loose, it's already too late because the gear can then rub against the crankshaft.

Thank you for your assessment of the situation; I will review it and report back!

AHF is actually quite straightforward in that regard.

Best regards, Rainer.