Lee,
This forum taught me how to do this on the M103, and it works - no need to touch the tensioner. Can this also be done on the M104 -is the alternator bracket/mount the same as the M103?

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)