I have not yet had to do one on the M102 but the procedure would be similar to that on an M103 and M104 which I have done.

Loosen the 17mm bolt in the centre of the tensioner and unwind the adjuster until the belt is loose and can be removed. The 17mm bolt can now be removed as well as any other smaller bolts that retain the tensioner. You may need to remove one or more pulleys (eg. steering pump or water pump) to allow access to remove tensioner.

Installation is the reverse procedure. Tension the belt such that the pointer for the indicator moves from one end of the scale to the other.

Since you are removing everything to get to the damper, it may be worth your while to also replace the tensioner itself. They are prone to failure after a period of time, especially when they have been disturbed.

Someone else who has done the job on an M102 may be able to offer more advice. At least yours being in a W124 should allow plenty of space to work.

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