Timing Belt Tension AJM Adjustment

Hello everyone,

First, the vehicle: Passat 3B5, 115 hp, 1.9L TDI with pump injector technology, AJM engine.

I've now read several posts about the timing belt replacement on the AJM engine, and I've obtained the instructions from ERWIN, but somehow I don't quite understand the part about how to properly tension the timing belt and then check and adjust it.

I've already done timing belt replacements on a 55hp Golf diesel and an Audi 80 TDI with a 1Z engine, but I've never felt as unsure as I did with this AJM engine. It started with the separate hydraulic tensioner. On the one I removed, you could press the spring pin with a firm thumb and simply insert the retaining plate. Based on that pressure, when I tried to tension it for the first time, it made the two-hole nut driver slip out of my hand, and a new hydraulic tensioner was needed. I couldn't push the pin back into its locked position. NIT also casually states that you need a new one if the pin extends completely.
After I learned how much force the hydraulic clamping element could exert, I approached the task with the necessary respect.
Following the instructions, I aligned the KW (front axle) and NW (rear axle), but I had to rotate the NW towards the rear wheel to be able to insert the alignment tool into the hole in the head. (The mechanic who had performed the last timing belt change had used paint markings instead of the tool, which also resulted in the car being slightly slower (195 km/h instead of 205 km/h according to the speedometer). I didn't take this too seriously and attributed it to the engine's wear.)
Water pump, hydraulic tensioner, and tensioner pulley replaced. The serpentine belt was placed over the water pump, tensioner, crankshaft pulley, and alternator pulley, and the idler pulley was installed on the new tensioner.

The tensioning itself isn't magic, but controlling it after the engine has rotated twice presents me with unforeseen problems. After the second rotation, I can disconnect both the KW (eccentric shaft) and the NW (crankshaft), but the 4mm (+-1) clearance isn't there. I then used a 6.5mm drill bit, as suggested in the forum, to correct the clearance. What's not clear to me is whether I also need to loosen the three screws of the camshaft sprocket when making this correction. The repair manual doesn't mention this if the timing marks are aligned. It only says to loosen those three screws if the NW cannot be aligned. So, I corrected it without loosening the three screws. After manually rotating the engine four times and the clearance was still correct, I drove the car. It pulls perfectly well up to 3600 RPM, then it becomes sluggish, and it cuts out at 3900 RPM. Even going downhill, it won't go faster. In addition to this, there's also a noise https://community.dieselschrauber.org/en/viewtopic.php?t=25359.
While trying to find the cause of the noise, I measured the distance between the tensioning element and the tensioner pulley last night with the engine hot, and I was able to insert a 1mm drill bit. So, it should be okay. This morning, I checked the distance with the engine cold, and I could only insert a 3mm Allen key – I used it because the angled part fit into the gap, and I could still hold the long part. While inserting the Allen key, it got stuck, and when I pulled it out, I pushed the stop plate of the tensioner slightly upwards. When I measured again, the distance was now 4-5mm.
How is that possible? How can the distance change if a lever is applied in the gap between the hydraulic clamping element and the tensioning roller?
The tensioner is fixed with a bracket (20 Nm + 45°). If I press against the tensioned timing belt, shouldn't the distance immediately decrease again due to the counter-pressure of the timing belt?

Where did I make a mistake? And if the noise indicates a too-tight timing belt, where is the tension coming from if the clearances are within the specified tolerances? I thought that maintaining these clearances would guarantee the correct timing belt tension. Is there a method to measure the tension? I would appreciate any helpful advice.

With puzzled but friendly greetings.

MichaelJ

Hello Michael,

As far as I know, all the manufacturer's specifications are given under cold conditions.
Therefore, these values are not valid at warm temperatures.
When warm, the tension rollers need to travel a greater distance because everything expands.

I would check the tensioner for the ribbed belt.

SG.

Thank you for the tip, but I have already taken that into account. The 1mm measurement is for the warm/hot engine, and the 4mm (+/- 1mm) is for the cold engine.
I made the ZR change and adjusted the settings after the car had been parked overnight and for half the day.

Hello MichaelJ,

In my ATJ (similar to the AJM), I made a note in my maintenance log that after adjusting the measurement (4mm) on the tensioner, it needs to be waited on (5-10 minutes) - even after loosening it and rechecking.
I'm not entirely sure why I wrote this down, but I suspect it was because I observed that after adjusting something with a wrench during the setup process, a certain amount of time passed before the component returned to its working position.

Perhaps this is another perspective to consider.

Bye.
peace

Yes, the waiting time is very important.

Quote:

I'm not entirely sure why I wrote this down, but it was probably to observe that after using the wrench during the adjustment process, a certain amount of time passes before the part returns to its working position.

This is due to the inertia of the damper, or tensioner. It works similarly to a shock absorber. When it's compressed, a liquid is forced out of the pressure chamber through a calibrated opening. And that takes time. You can clearly feel this when you press the tensioning element during disassembly to insert the locking pin.

I also experienced those squealing noises on my AJM engine during the last timing chain replacement. After a trip of about 4,000 km, they disappeared.

I've also experienced these noises occasionally in other vehicles of the same type. It's unpleasant, but they usually disappear again.
Of course, the prerequisite is that everything is 100% okay.

Quote:

After the second rotation, I can disconnect both KW and NW.

According to RLF (presumably a technical standard), the motor should be disconnected from the rotation while it is still in motion.
The purpose is to ensure that the belt is taut in the drive section. If it is not taut, the impeller will lag behind.

Since it's actually quite difficult to get that right in practice, or due to chance, I personally proceed as follows:

- Rotate the motor several times and insert the lower locating tool (KW).
Therefore, the KW is blocked.
- Place the ignition key in the ignition switch and turn it counterclockwise, against the direction of engine rotation.
Pre-tension the ZR slightly, enough to simulate a normal rotation, but not more.
more.
In this state, the NW connection must be disconnected.
- Then, tighten or check the central nut of the water pump.

That saves a lot of pointless spinning.

Hello,

First of all, thank you for the advice. To get to the bottom of the noise, I took everything apart again. Even without the ribbed belt, the noise was still there, so I then completely removed the timing belt. In the process, I noticed that the tensioner pulley had come loose . Although I'm sure I tightened it with a torque wrench, it shouldn't have come loose - or are the screws inserted with a locking compound? After tightening it again (this time with Loctite), the pulley has some play and will be replaced again .
The next assembly error I probably made was with the tensioning roller. Impressed by the power of the hydraulic tensioning element, I didn't loosen the nut enough, so it wasn't the element itself but me who pushed the tensioning roller into position. That couldn't work. Now that I've really only let the tensioning element push, and tightened the nut in the correct distance position (6.5mm drill bit), the distance between the tensioning element and the tensioning roller remains at 4.5mm in the cold state, no matter how many times I rotate it .
Unfortunately, nothing has changed regarding the lower maximum speed in 5th gear .

Quote:

After tightening it again (now with Locktite), the bearing has some play and will be replaced again

.

The pulley has a solid, one-piece core. Nothing should have happened to it.

If I were you, I would replace both studs after that incident.

The tensioner is a weak point. I generally replace it.

Loctite can be used, but it's not strictly necessary. And be careful not to let any of it get into the bearing.

Hello BM,

I had already replaced the bolt during the first replacement, but I'm putting in a new one again. In my AJM engine, only the tensioner pulley has a bolt; the idler pulley has a screw that is always replaced.
What torque should be used when tightening the bolt into the head? The same as the nut?
I couldn't find anything relevant to this question. During the first replacement, I tightened two nuts and then screwed in the bolt until it was secure.

Regarding the idler pulley: it rotates very easily, turns a couple of times when you push it, and has some play between the outer and inner parts when tightened. The play isn't visible, but it's definitely noticeable. The old idler pulley and the replacement idler pulley have no play. I suspect that the idler pulley "wobbled" on the screw, causing the bearing to become damaged.

I hope it lasts until the oil change after Easter. Because the AJM is making a delightful gurgling sound .

Quote:

What torque should be used to tighten the bolt into the head? Is it the same as the nut?

Oh God, no. Tighten the stud bolt until it's fully seated, and then just a tiny bit further (about 2 Nm), so just enough that it doesn't come loose, no more than that! Actually, it would already be sufficient if it's just fully tightened. The rest is taken care of by the self-locking mechanism.
Just to make sure it's fully charged, you give it a very slight top-up.

Okay, to wrap up this topic - the idler pulley lasted until the end, and the squealing of the timing belt didn't change either. Unfortunately, I never got around to replacing the head gasket. Sadly, my Passat spontaneously suffered a cold deformation at 330,000 km . Technically, the front axle components were warped and attached to the body , and economically, it's a total loss }.

Except for the cylinder head gasket, everything else on my AJM engine held up, especially the third connecting rod bearing.