| How to change belts on 98 SLK230
Changing belts in easy. There is no need to pay someone to do it.
There are two belts. Of course, take the outer belt off first. Study the way it runs around the pulleys so you won't be scrathing your head wondering later how to run it when you put the new one on. I took a few pictures with my digital camera in case in needed them later.
Find the tensioner pulley. You will see a bolt in the middle of the pulley with a 15mm nut on it. I could not get my 1/2" ratchet and socket to fit between the nut and the fan shroud, so I used a 3/8" ratchet and still had a hard time getting it on.
Turn the tensioner counterclockwise until you can get the belt off a pulley. Since I had the car up on ramps to change the oil and therefore had the engine cover off too. I thought it looked easier to change it from the bottom. It took some effort to move the tensioner enough to get the belt off, the smallest pulley, which also happens to be the lowest pulley so it was easy to do from underneath.
Next, working from the top of the car, I took a 1/2" ratchet with 15mm socket and released the tension on the belt. The tensioner is located more or less in the middle of the pulleys on that belt. This belt came off easily - maybe 30 seconds.
To install the belts, just release the tensioner on the back belt first and rethread the belt. So the same for the front belts.
Before you start the car, make sure that the belts are properly seated on all the pulleys. If you are off one tooth on one pulley, you could break that belt, maybe both, and possibly a lot of other things under the hood. | 
