I just did the timing belt on my new used 1996 850 GLT Wagon. It took some time, but was not that difficult. I found it harder to change the serpentine belt, it is so tight!
Some tools required: metric sockets, 30 mm socket to turn crankshaft.
torx bits, 25mm, (30 mm-to remove plastic cover over spark plugs I'm not sure why this is necessary).
On mine, to release belt tension on the serpentine belt, you need a 3/4" square drive adapter - or, per someone elses suggestion here on the brickboard, I made my own tool out of 1/8" thick steel plate, cut out 1" x 1.25" section, 1"
section going into the tensioner on the diagonal, used large pliers (adjustable wrench would also work) to grip this piece and rotate the belt tensioner all the way until you can pin a nail thru the holes that holds it in the untensioned
location.
I followed the volvospeed.com instructions. The timing mark on the crankshaft pulley is on the timing belt drive pulley, a little 'V' cut into a tooth, nearest the engine side of the timing belt crank pulley. It is very small, I could easily see the other marks on the camshaft pulleys. I was able to work the new belt in behind the crank pulley without having to
remove the pulley to get the new belt on.
You need a 7" vise to compress the hydraulic tensioner slowly, over 10 to 15 minutes. I stuck a nail with the end bent 90 deg. to aid in pulling it out quickly once its reinstalled.
Just make sure you double check your timing marks line up by hand cranking the engine once or twice and reinstall the top cover to verify the marks are OK.
Then cross your fingers the first time you start the engine. I was pretty confident I didn't screw anything up and it worked out fine. Cost me $50 to do it myself, not including a new serpentine belt. Took me probably 8 hours - but I'm real slow, took breaks, spread it out over two days - wasn't really in a rush. I would say I now could do it again in half that time.