My car: Passat B5.5 PD130 (AWX), 2001, 190k miles, RHD, (extras: PD170 turbo, decat, Darkside Developments FMIC, EGR delete, and remap, Audi TT front calliper bracket, EBC discs (312mm I think) and yellow stuff pads, Eibach lowering springs, etc., etc.). The car isn't driven hard (no redline, always warmed, regular semi-annual oil changes with Castrol 5w40, etc.)
Note: My engine has a hydraulic timing belt tensioner damper.
I'm looking for some advice, ideally from a VW technician who is familiar with the timing system on a PD engine.
I left my Passat into a reputable workshop to have the timing belt replaced around July 2021. In late December 2022 (c. 10k miles later), the backing plate of the tensioner (the part that meets the hydraulic damper - see image
) snapped on startup. It was a Gates tensioner. Thankfully, no head damage occurred.
The workshop agreed to re-do the job and put it down to a faulty Gates tensioner. I got the car back in early Jan 2023. It ran fine, but started cutting out when approaching traffic lights (i.e., off-throttle braking). This happened 10% of the time at first, then after a two months it happened more like 30% of the time. The car also started idling erratically - sometimes when starting it would idle at 400-500 rpm, before coming to life at a normal idle; sometimes it would rev to 2k rpm on startup.
Upon getting the car back I questioned the timing belt tension. I noted that (a) the gap between the tensioner backing plate and the hydraulic damper was c. 12mm (versus 4mm recommended in the Haynes manual) and (b) the 'arm' on the tensioner used to adjust tension (the one you insert the circlip pliers into) was in the slack position. Here's a YouTube Short: Timing belt tension - AWX PD130 Passat
When I raised this concern, the workshop replied with: "there is no fixed adjustment on that belt. The hydraulic tensioner is the only adjustment, the rod pushes against the plate on the pulley to take up the slack on the belt. When the belt is fitted all the slack is on the adjustment side of the belt and when the pin is removed from the tensioner the ram pushes forward and tensions the belt... All you need to do is remove the pin from the hydraulic damper and that's it."
Then, in May 2023,
the exact same thing happened again on startup. Here is a YouTube Short (note, the car only ran for that video - I cut it off once I saw what had happened): Passat (AWZ) Timing Belt Tensioner Snapped
Image showing the most recent snapped tensioner and the tensioner arm position.
The workshop are now unwilling
to stand over it. They are no longer willing to accept that it is a tensioner malfunction and now believe it must be related to the modifications I have done to the car (listed above). In their words "the larger intercooler is probably causing the car to over-boost", which makes absolutely no sense to me. And again, just to emphasise, this workshop is highly reputable and I'm dealing with the head person who knows his stuff - they're a main dealer workshop for a Japanese brand.
If I can prove that they set the tension wrong, I should be able to at least get my money back and go elsewhere (or do it myself). But at the moment, they are adamant that they set it up right "having worked on loads of those engines over the years, without issue".
My questions are:
- Did they follow the correct tension procedure by just pulling out the hydraulic damper pin (and not adjusting the tensioner so that the gap between the damper and tensioner backing plate is c. 4mm)? If so, how can I prove this without an official VW workshop manual?
- Could a slack belt have caused the tensioner backing plate to snap on startup?
Thanks in advance.