You need a 19 mm socket and a 13mm socket. If you are removing the belt for any reason, you need an 8 mm Allen and something to hold the fan clutch (a coat hanger wire for older (pre 89?) models, strap clamp of some sort for later one.

Before removing tension on belt, note the small pointer (usually red plastic I think) that points to the "ramp" cast into the tensioner body. You will need to watch this pointer while loosening the tension.

FIRST loosen the 19 mm center bolt on the tensioner. This bolt holds the center of the tensioner firmly in place, and if you attempt loosen the tensioner with it tight, you will only break the link.

SECOND, while WATCHING the tensioner body, unscrew the 13mm "bolt" that sticks up behind the belt near the head. If the belt comes loose and the markings on the tensioner body DO NOT move back to at least the start of the "ramp", the rubber in the tensioner is shot and it must be replaced. You must watch while loosening, as when you pull the 19mm bolt, the pointer will fall off, it is splined and fits anywhere. It will stay in place if you do not remove the tensioner though.

To remove the tensioner completely you must remove the bracket across the front I think (hard to remember at the moment), maybe not. Some one who's done this more recently will remind me. Tensioner comes right off with the 19mm bolt out.

The bolt that actually rotates the tensioner body is linked to a d-shaped ring that goes on the back of the tensioner body, make sure you know which way it goes back on or it breaks off when you attempt to tension belt.

Going back in, install the ring on the back, put the bolt up through the hold with the round side of the "nut" up, install the pointer so it is at or before the "ramp" mark or where it was when you loosend it (old tensioner), or at the line before the ramp (new tensioner). Snug the 19mm bolt up a bit so the pointer won't fall down, then install the belt (you will have to push the shock over to get the belt on the pulleys), then use the small bolt to pull the tensioner up til the pointer is at the "tall" end of the "ramp" mark. Tighten 19mm bolt.

Not hard, but usually messy from the "normal" front of engine oil leaks.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!