ZR Change Interval: Questions and Answers

Hello,

Given the relatively frequent timing belt failures in TDI engines, even with slight overruns of the recommended replacement interval, I wonder how VAG can determine such precise and "demand-based" intervals.

Let's consider the extreme cases.

"Representative vehicle with approximately 90% highway mileage, mostly driven in the highest gear."
-> Primarily used during rush hour with more stopping than driving (where diesel engines have the greatest fuel efficiency advantage over gasoline engines!).

...it becomes clear that the number of engine revolutions and, consequently, the wear on the timing belt (abrasion, bending/shearing) can vary significantly from vehicle to vehicle within a single timing belt replacement interval.

IMO, maintenance intervals should be based on the worst-case scenario, which in this case would be the daily peak usage with a low proportion of out-of-city travel.
Then, theoretically, the lifespan of a representative vehicle's engine could be significantly longer, perhaps by tens of thousands of kilometers, compared to something like a taxi engine.

Does anyone know to what extent VAG has considered these aspects when determining the maintenance intervals?

Does the wear on the timing chain (ZR) result only from the total number of engine revolutions, or is it also influenced by the tensile load?
At the very least, the high-pressure pump (HPP) transmits the "pressure pulses" that generate the injection pressure, which increases with engine speed in both gasoline direct injection (GDI) and diesel engines.

Does a ZR possibly degrade over time?
-> Higher tensile stresses due to speed limitations on Autobahn (motorway) sections, or...
-> additional engine revolutions per kilometer in urban traffic.
roughly the same speed, meaning that the maintenance intervals are quite suitable for both taxis and company cars, ensuring that even the latter do not exceed their due dates.

Are there any known patterns suggesting that "premature" timing chain failures tend to occur shortly after the recommended replacement interval, and are these patterns more common in vehicles primarily used for short or long distances?

(I hope you can mostly understand my sentence structure... today I'm just not able to create anything more understandable ).

Hello Ulf,

I believe that the timing belt itself rarely fails on its own. More often, it's due to improper handling caused by faulty tensioners, incorrect or insufficient tension, misaligned pulleys, and corresponding wear on the belt flanks, oil leaks, etc. The result is always a torn timing belt and a damaged engine head. The components that cause wear will show a small difference between city driving with many temperature cycles and shorter but higher overall stress from highway driving.

My assumption is that with highly engineered timing belt components, service lives in the 200,000 km range could be achievable. However, the manufacturer likely keeps the extra cost of those parts, which is around €12.57. A negative example is the 1.6-liter gasoline engine from Opel, where timing belts fail before reaching 60,000 km, and that's in a gasoline engine.

Besides, the workshops also need to make a profit.

Or do you think a design like the central timing belt screw would be acceptable in an Airbus commercial aircraft?

Best regards,
Christian.

Hi Ulf,

also ich denke, dass es eine Mischung ist zwischen "Laufstrecke" und Belastung des Riemens ist. Ein Motor, der nur Stadtverkehr abbekommt, legt ja pro km locker 2 bis 3 mal so viele Umdrehungen hin. Beim Zahnriemenwechsel, erkennt man gut den Abrieb des Riemens zwischen den Zähnen der Räder, und dieser Abrieb ist IMO von der Anzahl der Motorumdrehungen abhängig. Der Verschleiß der Spannrollenlager etc. ist IMO ebenfalls von der rpm-Anzahl abhängig. Dementsprechend dürfte es hierbei schon einen gewaltigen Unterschied machen, ob der Wagen zu 90% im 5. Gang oder zu 70% im 1-3. GanThe risk was taken.

Of course, there are also stresses from sudden acceleration and deceleration (similar to what happens with a "jerky" driving style -> Rucken -> F = m x a). I can imagine that such forces weaken the fibers of the belt. Consequently, there is a certain number of "cycles" or "tolerances" available before component failure . I am convinced that timing belt failures (when they are not due to material defects or issues with the crankshaft pulley bolt) occur particularly frequently with unqualified drivers.

Hi,

There's also another aspect to consider, aside from the owner's driving cycle:
And that would be the lifespan/usage period.
I often hear that the timing belt ages primarily due to the simple factor of 'time.'
Sure, please provide the text you would like me to translate from German to English.
It's better to drive 120,000 km over 3 years than 60,000 km over 10 years.


My Audi still has a 120,000 km service interval (which is probably why those otherwise good engines kept failing).
I plan to have the first timing belt replacement since I've owned the car (since 9/2002) – it would then be at 60,000 km.
He has driven 170,000 km, and I want to replace the water pump for safety reasons, as well as the tensioner pulley, of course.
Here's a question for the experts:
Is that too cautious? Who knows more about this engine?

'My dad works at Audi and he also drives a car from the year 1996 with a 140 hp AEL engine. He says: For these engines, it's generally necessary to replace the water pump, and then every 100,000 kilometers, you should discard the belt.'

This is just a general guideline. If you're only driving in city traffic, you might want to adjust it slightly earlier.

The problem here was with the tensioner pulleys at the beginning. A part broke off from a bracket designed for adjusting the pointer due to belt wear, and that's why we're seeing all these motor failures...

The tensioner rollers that are now available have already been modified, but it's still recommended to replace them around the 100,000-mile mark, as some water pumps have failed shortly after reaching this mileage.

I can't complain about my timing belts.

First service at the 'VW workshop' at approximately 90,000 km.
Replaced: all belts and ONLY the tensioner pulley.

Second oil change at 210,000 km, performed in my own garage.
replaced: everything that rotates has been changed, the crankshaft pulley bolt is still original, the bearings of the tensioner rollers have already expelled a lot of grease, the timing belt tension was already at its minimum setting, and failure was imminent.

Driving routes: Mostly full throttle on the highway (Autobahn), with a lot of country roads.

Conclusion: It keeps running and running! Now with 240,000 km on the odometer.

Hi,
"I'm currently only driving around 20,000 km per year. Last year, the rear timing belt broke at approximately 110,000 km. That already suggests the influence of age."

@golfggott: Are you familiar with the thread about the three-piece camshaft? In that thread, a part of a tensioner roller broke off. Is this a similar case? And if so, where did that old roller come from, considering the problem was supposedly resolved long ago?

Hi,

@GolfGott:

Thank you, that helps me quite a bit!
That means, in my case, that I will definitely change it this time at 60,000 km - because the water pump would then have been running for 170,000 km. The Audi dealer certainly didn't replace it when I bought the car (at 110,000 km).
I hadn't insisted on it either.

P.S.:
I would also be interested to see what Christian writes!