Timing Belt Failure: Early Signs on 1Z Engine

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

"Hi,"
During a routine inspection, a crack was discovered on the back of the timing belt on my Audi 80 1Z (Image 1). The timing belt has been driven for 65,000 kilometers and is 3 years old. It was replaced at that time along with the tensioner pulley and idler pulley by me, following the manufacturer's instructions. Approximately 5,000 kilometers ago, I replaced the fuel injection pump, and the timing belt was in good condition then.
After disassembly, the following additional anomalies were observed:
- The timing chain shows uneven discoloration on the gear side (Image 2, left), a dark stripe on the engine side, and overall a brownish color due to wear, similar to an old timing chain (Image 2, right).
- The wear and tear on the rear panel (labeling) is more pronounced compared to an older unit.
- The tensioner is a bit stiff compared to an older one.
The ESP wave and intermediate wave have no radial play. The ZR (presumably a component) was running on the edge of the tensioner pulley, in the direction of travel.
The bevel gear (KW), spur gear (NW), and pinion gear (ESP) should be aligned in parallel. Using a ruler (level) and gauges, I found a deviation of less than 0.1°.
Does anyone have any ideas about this image (crack and discoloration)? I've never seen anything like it before.
Of course, the timing belt will be replaced.
hg
Herbert.

"I've only seen cracks like these on very old belts, 8 years or older. I don't think it's due to foreign objects. Take a look at the seals to see if anything is starting to leak. Gates should be reliable without a doubt! Which tensioner are you talking about? Was it purchased as a set?"

Hi there,
First of all, thank you for the response! As I mentioned, the belt is 3 years old, and the expiration date on the packaging was far in the future. The tensioner pulley and idler pulley are also VW/Audi original parts. The manufacturer of the tensioner pulley is Litens, Canada (like all the previous ones). The Simmer rings should be okay; everything appears to be dry.
hg
Herbert.

"It's likely that some tar or similar substance was unevenly adhered to the pump impeller and has spread. Regarding the crack in the belt, I've only seen such cracks on the motor side so far – this probably indicates a thermal process!"

Hi,
I can rule out tar or similar dirt.
The only thing that comes to mind regarding a thermal issue is the relatively stiff tensioner pulley, which could cause belt slippage. This might also explain the more worn-out back of the component. However, there was no squealing from the timing chain. The intermediate shaft can be easily turned. The motor itself is thermally okay.
Can the manufacturing date be determined from the labeling on the Z-connector (gate)?
hg
Herbert.

Hi,
The discoloration on the timing chain cover (on the engine side) is likely due to a leak from the ESP shaft. A new timing chain, with only 15,000 km on it, shows the same problem. Upon closer inspection, the hub behind the ESP pulley and the inside of the pulley appear slightly damp.
I will be getting the ESP (AT part from 2011) replaced.
hg
Herbert.

Hello,

Herbert wrote:

Does anyone have any ideas about this image (the crack and discoloration)? I've never seen anything like it before.

die Verfärbung würde mich jetzt nicht weiter stören, auch die Rückseite vom Riemen sieht für mich nicht unnormal aus. Aber der Riß Was ist das denn?? Ist das der einzige am Umfang? Sowas hatte ich auch noch nie. Wenn Risse, dann oberflächlich überall auf dem Rücken und über die ganze Breite (hab mal nen 12 Jahre alten 35i gekauft, der scheinbar noch den 1. Rieme(which he had put on it).
Do you perhaps have any enemies who might sabotage timing belts with a pocket knife ?

Best regards, Uli.