Go to
Liftbars for info on the PKtensioner.
The factory tensioner is adjusted cold and releases tension due to the bi-metal washer stack when it gets hot. This is to compensate for the aluminum block/head growth after it gets up to Operating temp. Overly tight adjustment or a factory tensioner that is not working correctly (bi-metal washers not collapsing as designed, etc) can cause accelerated wear on the gears, and water pump bearing.
The Pk-Tensioner uses parts from the Audi V8 (the tensioner) and a custom bracket to replace the factory device. The Pk-Tensioner relys on a constant tension that is self-adjusting. This design is intended to maintain a constant and consistent tension (cold or hot). It also has less parts and requires less maintenance.
I have had my Pk-Tensioner for 2 years and about 40k miles. Not a problem . Many other people have used them as low cost replacements for the factory parts.
On a 32 Valve car breaking a timing belt is a much more expensive problem, however for most (US) 16 valve cars breaking a timing belt is more of an inconvenience than a expensive valve replacing nightmare.
You may be able to rebuild your factory parts. The bearing in the idler rollers are fairly common place if you can get the proper ones pressed in. That can save you some $$. The gears will be the most expensive part of it all. Confirm your gears are round tooth (new style) and not the 'square' tooth (old style and I believe no longer available).
Gear replacement should include both cam gears, the oil pump gear, and the crank gear.
In any case, I believe the only 'special' tool you need would be a flywheel locking tool. You probably can borrow one however a new one is about 40 bucks and a good addition to your '928 ' toolbox.