Siemens SIDOOR AT40 System Manual page 236

Geared motors
7.2 Installation
2. Mount the deflector unit, if necessary with a mounting bracket.
Ensure that the drive pinion and deflector pulley are aligned when doing so. They have to
be exactly aligned to ensure a long drive service life.
3. Pass the toothed belt over the deflector pulley and drive pinion. Place both open ends of
the toothed belt in the door clutch holder. Screw the door clutch holder together.
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AT40, ATD400V, ATD400K, ATD4xxW, ATD400S, ATE250S, ATD400T
System Manual, 06/2016, A2B00096162-AN