Timing Belt Tensioner for PD Engines

Hi!
Today I changed the timing belt on my car. However, I'm now a little stuck when it comes to adjusting the tensioner for the actual tensioning pulley.
Specifically, an adjustment value of 4 ± 1 mm must be maintained between the clamping device and the tensioning roller. I followed this instruction. Then, I manually rotated the motor three revolutions and checked everything. It was perfect. Next, I disconnected the central connector for the PD elements and let the starter motor rotate it. After that, I measured again and only had an adjustment value of 2 mm. All of this with the engine cold! Have you experienced anything similar?
The repair manual states that the measurement can be reduced to 1mm when the machine is warm, but that's not happening in my case. I'm concerned that I might have problems with the warmer machine because the tensioner roller won't be able to give way enough...
I hope you can imagine which components I'm referring to...
Vehicle is a Polo 1.4 TDI PD with engine code: AMF.
The following parts were replaced: the water pump, idler pulley, tensioner pulley, and belt. The tensioning device itself is still the original one; it's not normally replaced and hasn't caused any problems so far.

"Thank you!"
Dirk.

brezelmann01 wrote:

Then I manually rotated the engine three revolutions and checked everything. It was perfect. Then I disconnected the main connector for the PD elements again and let the starter motor spin it over. After that, I measured again and I only had an adjustment value of 2mm. All with a cold engine! Have you had similar experiences?

HI.

I'm not sure how the measurement changes with the "belt length over the pulley."

But I know that the roller is under more tension when you rotate the motor in reverse.
So, if the compression caused the crankshaft to rotate even a little bit backward after the starter was switched off, the tensioning device will be in a different position than when it rotates forward – this is perfectly normal.

Hi Ulf!
That's another brilliant idea from you. It sounds very logical. I'll try adjusting it manually again tomorrow morning. Hopefully, that will correct the 4mm issue.

Dirk *who can now finally get some sleep*.

I also recently completed that procedure. However, I didn't do the starter motor test. I think I have a good understanding of the 'theory' behind it. On the other hand, if the setting is correct and you've made several turns with a wrench or by hand, and the measurement was right afterward, why shouldn't it still be accurate after 500 or 1000 starter motor rotations? If that were the case...
You probably didn't tighten the tensioner properly.

Is it fun to change the ZR on a PD or what?

Well, fun is kind of a tricky thing. Actually, the biggest effort comes from dismantling everything around it, the cursing – because the tool fell into the box with the coolant – and the annoying adjustment of the voltage. I really struggled with that, because it constantly changes when you tighten the roller. You probably have to do that hundreds of times to get a feel for "generously adjusting 4mm" .
But otherwise, I think it's still okay. Or wait... let me please give another statement about it tomorrow evening, in case my engine is still intact then .

Dirk.

Well, getting rid of the tension all around...

'Keep your chin up, it will be alright. Mine has already survived three trips from Southern Thuringia to Munich and back without any engine damage...'

To make tightening easier, a 6 or 6.5 mm drill bit is used.
"So that when the tension is released from the tensioner, it passes through the damper, and then tighten the tensioning roller."

Then rotate the motor two times ----> now you should have approximately 3-5 mm of clearance.

Okay, so I just wanted to give you a little feedback on what I did.

Unfortunately, Ulf's assumption was not correct; the measurement remained too low. I then readjusted everything several times until I finally got it to just under 4mm, which is almost perfect according to the repair manual. Then I assembled everything and took it for a ride. However, after about 15 minutes of spirited driving, the measurement shrank so much that the belt tensioner was at its limit, leaving less than 1mm of space. The belt was therefore too tight. I then disassembled everything again and followed Steffarn's advice. I used a 6.5mm drill bit as a gauge. After rotating it, I got to 5mm. I just took it for another ride for about 15 minutes (but slower), and now there are still about 1.5-2mm of space, even with the engine warm. So, I think it's perfect. I believe that the target value of 3-5mm specified by VW in its repair manual is very risky if you take the lower limit (i.e., 3mm)!!! I just hope that the tension adjustment screw on the tensioner will forgive my numerous attempts and not fail prematurely.

See you later, and many thanks to everyone involved!
Dirk.

brezelmann01 wrote:

Unfortunately, after about 15 minutes of driving, the size decreased so much that the belt tensioner was at its maximum limit, and there wasn't even 1 mm of space left.

The belt was therefore too tight.
However, the belt doesn't shorten; instead, the block expands more than the belt does, which pushes the tensioner towards its limit when the engine is hot.

It remains a mystery why the measurement changes when using the starter organ. Or wasn't there something about oil pressure damping in the PD belt tensioner?

I can't really explain why the measurement is getting shorter. The only possibility I can think of is that the belt might be engaging more tightly with the gears when it's spun rapidly and forcefully by the starter motor, compared to how I'm turning it with my own hands.
Hmm... do you think there were problems with the shock absorber before? I don't remember anything about that. But if anyone has the link, please post it!
@Ulf: What distance should there be for your auxiliary drive unit (ASZ) according to the repair manuals? Have you ever checked it while the engine is hot? You can usually see it - at least in my case - if you remove the upper timing belt cover. I'd be interested to see how much it shrinks.

Dirk.

brezelmann01 wrote:

Hmm...do you think there were problems with the shock absorber before?

No, just as a design feature: if hydraulics are involved, then their movement (theoretically) could change the purely mechanical adjustment (without oil pressure) once there is oil pressure – so even when playing the organ.
But it's purely theoretical on my part, without any knowledge of the hydraulic function.

Quote:

@Ulf: What distance should there be according to the repair manuals for your auxiliary drive unit (ASZ)? Have you ever checked it with a hot engine? You can - at least in my case - see it if you remove the upper timing belt cover. I'd be interested to see how much it shrinks

.
I don't have a manual... what I see when the upper timing cover is removed is a metal pointer next to/above the tensioner pulley, which moves back and forth in front of a fixed metal part (with a likely marking gap) when the engine is rotated forward and backward.

When the engine cools down after being turned off, the needle (indicating hours) also moves a few millimeters. In winter, when the engine has cooled down, it points to a different position than in summer.

Quote:

No, just as a design feature: if hydraulics are involved, its movement (in theory) could alter the purely mechanical adjustment (without oil pressure) once oil pressure is present – and that would even happen while playing the organ. However, this is purely theoretical on my part, without any knowledge of the hydraulic function.

Sure, that's conceivable. However, in my case, the belt tensioner is not connected to the engine oil circuit. It's a separate component, similar to a very small shock absorber.


naja, wie auch immer. Motor läuft jedenfalls perfekt. Bin gerade noch mal Autobahn gefahren. "Thank you!"

Dirk.

While this is an older topic, I'd like to add my comments here.
I replaced the timing belt last week (115 HP PD engine, ATJ code, manufactured in May 2000, with 90,000 km on the odometer).
Since the temperature in my garage was just under 10 degrees Celsius, I adhered to the upper limit of the tolerance and set the gap to 5 mm. (By the way, I measured the gap before removing it, and it was 8.5 mm!) Today, I re-measured the gap with the engine warm, and it was slightly more than 1 mm. (According to 'How it's done,' the gap can decrease to up to 1 mm when the engine is warm). So far, so good. However, I wonder what the gap will do in the summer when I drive over an Alpine pass at 30 degrees Celsius in the shade; then the engine will certainly get hotter than it is now in winter. I can imagine that the tension could become too high and the timing belt could break if the tensioner roller is fully engaged.
What do you think, should I make the gap a little wider?
best regards,
Hardy.

Hi,

Let's wait and see for now. Usually, the situation "resolves" itself somewhat after a few kilometers.

Best regards, Rainer.

Thank you for the quick response.
Okay, I'll wait, but I've already been driving around the area for a week (about 300 km).

Regards,
Hardy.

Hi!
My suggestion would be to let the warm engine idle and observe the gap while it's running. As Ulf mentioned before, I believe that an unfavorable shutdown of the engine can sometimes result in a slightly higher voltage at the timing chain.
And otherwise, I would definitely follow Steffarn's advice again. Even after more than 10,000 km, the belt is still perfectly tensioned... So, thank you once again at this point!

Dirk.

P.S.: In my case, the belt did NOT become noticeably looser after I started the engine for the first time with a new belt .