Porsche 928 Workshop Manual page 196

15
Engine/Cylinder Head, Valves
928
Loosen nut on adjusting screw and turn adjusting
screw until the drive belt tightness is correct. Tighten
nut again. Turn engine two more turns and recheck
drive belt tightness.
Tightening screw = tightening belt
Loosening Screw = loosening belt
Note
Never turn engine anticlockwise, since drive belt could
jump out if its tightness is insufficient.
15.18d
Checking and Adjusting Drive Belt
Printed in Germany