normcoreashore

A quick note on my recent hydraulic belt tensioner issues, for any future lost souls who may encounter this particular issue:

I just completed a water pump and timing belt replacement on my '94 968 Coupe a few weeks ago. The main water pump bearing seal blew out while I was driving, lost all fluid and engine temp quickly spiked. Luckily I was able to stop in time, let things cool and get it towed.

When it came time to replace the timing belt, I reinstalled the hydraulic belt tensioner as I have before, and discovered that it was, for some reason, no longer pulling the belt as tightly as it should.

The car started and ran, albiet roughly as the timing now had some slop to it, and this was certainly not a road worthy fix.

After some experimentation and observation, it appeared that the tensioner was not extending as far as it had been previously. Perhaps the tensioner is failing? I didn't measure its maximum throw the last time it was fully extended. Perhaps the belt is a tiny bit longer? seems unlikely, they were both ordered from 944 online and looked similar enough, though I did not measure or compare them directly.

In any case, this strange gap was discovered after everything was installed, and I needed to drive the car the next day. Luckily I had recently made a cut in the plastic belt cover, which left just enough flex in the cover that I could bend it out of the way without breaking it and carefully extract the tensioner. (this was only barely possible and took several tedious attempts)

Of course, I only realized after I had removed it how sketchy it was to unthread a bold in here hovering right above the belt gallery. One dropped part here and I wouldn't be able to extract it and thus would have to dismantle and re-assemble much of the job. (used a telescoping magnet tool to catch the bolt during the unbolting process.. vey risky)

After removing the tensioner, I extracted the plastic spacer that sits against the belt tensioning lever. Then created a new spacer from a piece of plastic stock. We eyeballed the part and added a few extra millimeters of width. My fathers woodshop and mechanical engineering skill made this a simple undertaking.

Re-installing all of this was a bit stressful, as I now realized how much I would screw myself by dropping a bolt or the spacer. The spacer was fabricated with a slight taper so that it would stay in the inverted hole with a slight friction fit. My father and I also devised a system where I used a metal wire against the attachment stud to hopefully catch the bolt in case I fumbled it here. A lot of consideration to avoid dropping bolts in hard to reach places, but still less work then tearing everything apart to get better access at this point.

I checked the belt tension with the Arrnworks tool and it was perfectly in spec. The tensioner appears to work the same, as long as it's not topping out in it's throw. But I have no idea why my tensioner appears to be suddenly topping out at a lower point now... In any case, the fix works great, and I'll keep rolling with this custom spacer for the foreseeable future unless something changes.

Apparently these tensioners are no longer available? I read that news elsewhere on the net while looking for a replacement. I really hope that's not the case, but if you happen to find yourself in a similar situation with a partially failing tensioner, this is a suitable fix, and relatively easy with access to basic shop tools.



A 9mm wrench was able to be pressed into the gap between tensioner and tensioning lever.. that's about how much play the tensioner had before the timing belt appeared reasonably tight.



Chopping a plastic dowel in my fathers wood shop



Quick and improvised lathe for this relatively simple part



improv lathe


stock spacer on the right, custom extended spacer on the left. Note the tapered insert cylinder. This enables the part to stick itself in the hole and prevents it from falling out during installation



stock spacer on the right



Here it is in place



a little closer look



Method of using a small wire to catch the bolt in case I can't thread it with one hand at this precarious angle