Engine Failure at 140 mph (1Z, '96)

Hello,

So, now I've paid my dues, endlessly.
Yesterday evening, while I was driving on the highway at 140 km/h (approximately 3000 RPM), the timing belt suddenly broke. This happened because the crankshaft bolt had come loose, causing the timing gear to detach from the crankshaft.
Now, the question that's been on my mind, especially since I haven't been able to take a look at the engine yet:
What is likely to be broken?
Most likely, a piston or possibly multiple pistons have collided with the valves. This would have certainly bent one or more valves. But what about the pistons themselves, the connecting rods, or the crankshaft bearings? Did they also experience some impact, or did all the energy go into the valves? Has anyone had experience with this?
And how can I check if the connecting rods, etc., are still in good condition?
I've already used the search function here (you learn something new every day ), but I couldn't find anything similar.
Best regards,
Kisses.

Rudi had pointed out to you in your thread /viewtopic.php?t=9837&highlight= about the KW screw...
Too bad.

You won't be able to see the exact extent of the damage until you disassemble it.

Yep, that's a shame. Almost all the posts were pointing towards timing and, consequently, the kW adjustment. But no, it couldn't be that!

You won't be able to determine exactly what failed until you disassemble the machine. I don't know the machine's operating hours, but I would recommend replacing it. It's certainly possible that the pistons and connecting rods are fine, but there's also a significant chance that you've acquired something hidden that could cause problems later.
If you're lucky, you might only need a new Zk, but...

Yes, that's right, all the posts were related to the KW screw.
And I even disassembled the KW gear, saw significant damage to the spline, installed a replacement gear, adjusted everything, and it ran great, but unfortunately, like a complete idiot, I didn't install a new KW screw (but I did use plenty of threadlocker).
I could literally bite myself for completely missing that in the recommendations, and I should have been able to figure it out myself!!!!!!!!!!!!!!!!!!!!!!!!!!!
I don't know what possessed me last week.
Aber was hilft alle Selbstzerfleischung??? Nothing!!!
According to the ATM data from last year, the engine's mileage was supposedly 80,000 km.
Is the probability really that high that there are hidden damages?
Sorry.
Kisses.

I experienced the same damage.
I only installed a new AT head and attached a new KW wheel.

It has been running for 25,000 km without any problems.

and costs less than an AT machine.

Well, then I can still hope!!!

I'll pick up the box tomorrow morning and I'm excited to see what's inside!
My replacement ZK, which I had stored in the garage at home, is already on its way here via package. Hopefully, that will be enough!
How exactly is the KW screw tightened?
I've read very contradictory things about it.
Best regards,
Kisses.

@Kussi

In your case, simply replacing the Kw-screw and tightening it properly probably won't help much. You'll likely encounter similar problems soon after, and you'll probably end up completely destroying the motor. Before you reassemble the Kw-ZR wheel, you must first machine the Kw-stub!

It's a real shame that you ruined the engine through careless tinkering (you can't really call it proper repair work!).

@lappen

You are absolutely right; you can't really call that 'adjusting' or 'fine-tuning.' As I mentioned above, I'm just frustrated with myself about it!

I've now got the car in the garage and I'm currently disassembling the engine. As far as I can see, one valve is damaged or broken, and I'll check the others from underneath shortly.
The KW screw didn't just loosen; it completely broke off!
Is it likely a fatigue fracture, or did I overtighten the screw?
Actually, I tightened it with the torque wrench to 90 Nm and then another quarter turn, as I read here or elsewhere. I have really read a lot about that! (Except for once! )
Hm, what do you mean by 'planning' and why?
Assuming you're referring to the contact surface of the KW-ZR wheel on the KW shaft, right? If not, the KW gear would likely be unbalanced.
How do I get them perfectly flat using regular tools?
I think I may have read something about that before, but I don't remember where. So, if you have a link or any information about it, I would appreciate it.
Best regards,
Kisses.

...
The KW screw didn't just loosen; it completely broke off!
Is it likely a fatigue fracture, or did I overtighten the screw?

Tell me, where do you actually live? That screw can only be used once!
This is a stretch bolt that extends by a defined amount. Therefore, it can only be used once. The second time it is used, the bolt will be overstretched and will either break immediately or fail shortly thereafter.
...
Hm, what do you mean by 'planning' and why?
Assuming you're referring to the contact surface of the KW-ZR wheel on the KW shaft, right? If not, the KW gear would likely be unbalanced.

If the KW wheel has been damaged, it should be replaced with a new one, and the KW hub should be resurfaced to a flat surface using a special tool.
The power transmission from the crankshaft stub to the gear is achieved solely through the surface pressure between these two surfaces. Therefore, the stub and the gear must be perfectly flat against each other.

How can I get them perfectly flat using regular tools?

Not at all -> Specialized tool -> VAG workshop or engine reconditioner.

I've seen a few ACV engines with broken timing belts due to a faulty water pump.
"It's usually possible to get it running smoothly again. Most often, only the valves are bent, and you can see nice markings on the piston crown. As long as the piston crown doesn't have any cracks, it can stay in place. I always replace all the valves and valve stem seals, and then the engine runs again without any further problems! Many of these T4 vans (all 2.5 TDI models) often have mileage exceeding 500,000 km. One van that had a broken timing belt at 385,000 km due to a water pump failure is still running with the same engine (just new valves) and has now reached 1,223,000 km, and it's still running well."

kisses

The planning tool is a pen with a precisely fitting sliding surface that is screwed into the thread of the KW (likely referring to a specific component).
A milling cutter is then mounted on the sliding plate, and this cutter is used to "face-mill" the front surface of the crankshaft.
I did it like this on my old 1Z engine because the new timing belt pulley was wobbling after the old one had become loose.
The problem isn't so much the timing belt pulley itself, but rather the pulley with the vibration damper that is screwed on externally, as it has a larger diameter and more mass.
The Passat with the 1Z engine subsequently ran for over 120,000 kilometers.
I got the tool from VW in exchange for a case of beer for the break room and a pack of cigarettes for the foreman.
However, I have a good relationship with the workshop.


Regards, nobbif.

Please provide the text you would like me to translate from German to English.

Passat 35i, 1Z engine, 420,000 km.
Passat 35i AFN, now with 200,000 km.

So, I had a used cylinder head installed about 3,500 kilometers ago. I had the crankshaft stub machined as best as I could, (I heard from two VW workshops that they didn't even have the necessary tools!), and now I'm driving the car.
It might just be my now overly sensitive sense of hearing/body awareness, but I always have a somewhat strange feeling when driving. Overall, the engine feels rougher than before, especially when I gently press the clutch pedal. It feels like it's running unevenly. It starts well, but it seems to have lost a bit of power.
But everything can be very subjective!
Anyway, the engine is running again for quite a while now, and I'm curious to see what happens next!
Best regards,
Kisses.

Hi Kussi,

Pay attention to your oil consumption.
It might suddenly skyrocket like a piston shooting upwards.
Often, the impact of the valves is so strong that it affects the grooves for the piston rings.
to be compressed.

But it doesn't necessarily have to be...