V6 TDI Timing Belt Tensioner: Broken Bolt.

I don't know whether I should be angry or happy.
If this mishap had happened to me a day earlier, I would be driving a VW bus with a trailer on the highway. One day later, I would be in Italy.

Vehicle: Audi Allroad, manufactured in October 2001, with 300,000 km mileage, engine code AKE, 180 horsepower TDI.

The day before yesterday, I intended to leave my father's house at midnight.
"When I realized that the servo wasn't working and the battery light was on."
Okay, either the serpentine belt is broken or the alternator is faulty.
It turned out that the tensioner arm of the serpentine belt had detached.
More precisely, it detached a few kilometers ago. However, it had to work its way through the plastic cover before it could completely detach.
I initially thought that the workshop foreman had forgotten to apply the Loctite threadlocker.
But when I went to Audi and bought the one-euro-eighty screw and tried to screw it in...
I soon found myself stuck in the threads. The remaining part of the broken screw was lodged inside.
I thought it was securely fastened and wanted to remove the bracket holding the wrench, which is screwed in from the back through the power steering pump holder. To get to it, you have to disassemble half of the car because otherwise you can't reach it .
However, the last Allen screw on the shock absorber at the rear axle stopped me.
I decided to stop fighting against this system because I found it boring.
So, I tried using the screwdriver to unscrew whatever was broken off from the threads.
To my surprise, I noticed that the screwdriver was getting closer and closer.
So, I had the second half of the eighty-one euro screw in my hand.
The other half is probably on the highway.
A red color was visible on the threads, likely Loctite red threadlocker.
According to the repair manual, this screw should only be tightened to 30 Nm.
I think I will still secure them with locking screws, though.
I'm not sure what to do with the seven Allen screws on the main vibration damper yet. I think they should probably be replaced.
I would secure them with blue Loctite.

Do you happen to know of similar issues, or was this an isolated incident?
I thought that with brand new cylinder heads, a thermostat, and a needle valve lifter,
"I don't expect any more repairs to be needed soon."


Oh yeah... Screwing outdoors at minus 7 degrees Celsius is exactly as thrilling as you might imagine .

That's perfectly normal; I experienced the same thing in early October. It's very convenient when you need the car for a move.
You don't need Loctite for that; the stub will come out easily next time. I had to use a right-angle attachment to drill into the stub and then use a screw extractor.
I also wrote something about it on Motortalk.

"The fact that the support arms are often replaced, either due to defects or recommendations, is evident from the fact that mine was in stock."
The root cause of the problem is actually the poor design of the connection between the tension arm and the pivot bolt. Because the spring element and the tensioner roller are not in the same plane, a moment is created that is only transmitted to the pivot bolt by the preload force generated by the screw. Due to the more uneven engine operation in diesel engines, this moment fluctuates in intensity, creating a fluctuating load. Over time, as the material of the tension arm weakens (which I can clearly see on mine), the preload force is lost. The tension arm then transmits its moment through the screw, which can only withstand a limited number of load cycles.

In October, the tension arm was not in stock, so we replaced the tensioning element as a precaution.
Around mid-December, the screw broke again. Now, a new arm has been installed. I checked everything again after two weeks, and so far, it's all still secure.

It happens sometimes. This isn't a design meant to last forever. Be glad you were able to get the screw stub out so easily.

And absolutely do not apply Loctite to the shock absorber screws. They are already extremely difficult to remove, especially if your predecessor rounded them off and reinstalled the old ones.

Thank you, Christians, for your valuable post.
Unfortunately, I also have the bad news that I will probably be involved in that again soon .
Unfortunately, I read your post too late and just installed the new screw.
If I had read this before, I would have waited until tomorrow to start assembling it.
and the entire unit was replaced.
I hope that at least Audi made a better screw.
"At least now I'll get the tensioner unit and replace it during the next timing belt change, which will be in 80,000 km."
If the screw holds for as long as .
Now my hope is fading that the 2.5 V6 TDI engine, aside from its well-known weaknesses, is actually a good engine.

If your suspension arm looks like mine, then the distance is more likely to be 2000 kilometers rather than 80,000 kilometers.
"This corner of the engine is completely cluttered; it looks like they forgot to install the power steering pump and then just slapped something else on top of it."
If you want to completely replace the condenser unit, you'll need to remove the air conditioning compressor and its bracket, which is possible. Then, you'll also have to remove the power steering pump. And as a "fun" addition, the power steering pump bracket is located underneath the oil cooler, so you'll also need to drain the coolant beforehand.
I left the wrench's pivot pin in place.

So, the arm looked pretty good, actually.
The only part that could potentially wear out would be the tensioner pulley, but it was replaced 40,000 km ago during the last timing belt change. It also showed no signs of play.
The surface of the tension arm that rests on this bearing, where the screw broke off, also looked very good. It appears there was never any friction on it.

Yes, this power steering pump bracket looked terrible .
It's not enjoyable when you can't see how a part is supposed to be unscrewed.
However, I'm sure there's a way to get into that warehouse from the back.
by removing the timing belt cover or the idler pulley.
Well, let's see.
Anyway, driving with that thought in the back of my mind is no longer much fun.

If you manage to do this, you're extremely skilled. The first time I tried, I also had to remove the mounting plate because the screw head was stripped, and I wanted to make sure it wouldn't fall into the timing chain. There's another screw with a washer on the rear of the bearing bolt; this will hit against the oil cooler or its bracket. It's difficult to unscrew because you can barely reach the screw from behind, and you can't hold the bolt in place from the front.

Yes, are you stupid?
Such a heavily modified piece of junk.
Then all I can do is hope that if the old screw lasted 300,000 kilometers,
The new one will last longer than 2000 km.
I also have an offer from a friend who said he could reproduce this screw for me using titanium. The price should be between 40 and 100 euros, depending on whether the screw can be made from a blank or needs to be machined from solid material.
I don't want to dwell on that right now.
Looking back, I realized that one or two engine starts prior, ...
I heard a loud bang. The stress will probably be greatest during startup.
And on top of that, it was minus 11 degrees Celsius.

Thank you very much, Cristian, for your help .

This issue was resolved differently by a Bosch mechanic I consulted with, as he completely unscrewed the entire thread when loosening that screw.
He re-threaded the damaged thread (since it was already ruined) to a slightly larger size and used a correspondingly larger screw, applying a minimal amount of Loctite.


Best regards,

Did he re-tap the threads on the 2.5 V6 TDI?
"How did he hold the material in place? There isn't much room left for trimming."


I took a closer look at the broken screw under the microphone. It's clear that the screw was no longer held in place by the thread locker and was therefore "working loose."
Auf der unteren Aussenseite der Gewindegänge, ist sie abgenutzt. Not above.
Furthermore, it is visible on the upper part of her neck that she has been injured there.
I suspect that the impact during startup, combined with the -11 degrees Celsius temperature, was what finally broke it.
I'm actually quite confident that my added screw securing method (I applied a full layer of blue Loctite to the threads) will...
It should last a little longer. At least, if it had already lasted 300,000 km before.
Why would it fail again after 2000 km, especially considering that Audi is likely aware of this problem and has probably focused on improving the manufacturing process?

No, it's in my car, a 1.9 TDI.
He didn't want to tell me how he had managed it.

But he charged a hefty price for it on the invoice.

The screw is a grade 10.9, roll-formed, and I don't think a titanium one would hold any better. However, I don't know anything about the susceptibility of titanium to stress corrosion cracking.
A properly engineered bolted joint will hold solely due to the clamping force, without the need for Loctite or any locking washers.
If the old tension arm no longer provides a flat contact surface or otherwise deforms, this force is lost. The screw remains precisely in place, but it becomes loose as a result. This has the well-known consequences.
Here's what my spring looked like after the second mishap:

Okay, now I understand what you mean.
Mine definitely didn't look like that.
While not quite as good as the new one, there were no signs of wear and tear, only slight impressions from being stacked.
You might be wrong, but if the screw has clamping force, then something like what happened with your worn-out clamping arm shouldn't have occurred, because the clamping arm and bearing should form a single unit. Only after the screw loosens could there be friction between the clamping arm and the bearing.

"First of all, I'm relieved that mine looked so good compared to yours."
Nevertheless, it will be replaced during the next timing belt change.

Thank you again for your support .

Yes, although I suspect that initially only a small amount of material was incorporated, but enough to prevent the screw from being completely tight. This allowed the connection to move, and things got really bad until almost all of the load was transferred through the screw, which then broke first at the beginning and later in one of the initial threads.
If one wanted to reinforce this, the cylindrical part of the set screw would at least need to be longer and achieve a tight fit in both the clamping arm and the bearing bolt.

Hi, just a quick question.
Do you guys have the free-running feature on the Lima?
I've already checked the alternator on my new one, and when I turn off the engine, the knocking sound disappears.
You can only hear it when you turn it off with the door open.
I think this is related to the clipped and removed bolts.
Sure, here is the translation of the text from German to English:

"MFG" stands for "Mit freundlichen Grüßen," which translates to "Sincerely" or "Best regards" in English. It is a common way to end a formal letter or email.

Our Lima vehicles come standard with a freewheel mechanism.
Furthermore, there's a jolt when starting up, meaning when all the components are rapidly brought up to speed at the same time.

Here is a picture of the idyllic winter life at minus 7 degrees Celsius .