Fan belt tension should be ±12mm (1?2in). Drive belt slippage can result in slow water pump and alternator speeds, but overtightening will reduce bearing life.
The mounting bolts are first loosened, and the alternator body tensioned against the belt, using the shaft of a hammer or similar if necessary.
This bolt on a sliding stop regulates the alternator position relative to the belt, and hence tension. Two spanners may be needed to undo it.
This alternator is being jammed in place by a bar while the bolts are finally tensioned.
Check with your finger to ensure the belt movement is within the manufacturer’s recommendations – normally ± 12mm (l/2in). Drive belt slippage can result in slow water pump and alternator speeds, but overtightening will reduce the life of their bearings.
