Giorgio,  Robbie's advice is 100% correct for running a motor on 220
volt 50 Hz power.  Both the speed and the motor inductive reactance
are 5/6 of the values at 60 Hz.  For the same mechanical horsepower
(proportional to torque times RPM), the motor will run hotter at 50 Hz.

Fundamentally, the motor cannot produce its rated horsepower when
run on 50 Hz power.  The motor can produce the same torque (without
overheating) at 93 volts, but at a lower RPM.  Putting on the bigger
pulley will take care of that factor, but will increase the torque that
the motor must produce (by the pulley ratio).  Nevertheless, because
the motor most likely has some mechanical power margin, it will
probably not heat up too much.  This has been the case, according to
one reader's posting.

When I lived in Italy, I used a transformer to operate a USA-made
60 Hz refrigerator on the 220v 50 Hz mains power.  The compressor motor
would overheat and shut itself off at 110 volts, but it ran fine at 95
volts.  (I removed some of the 110 volt secondary winding to reduce the
output voltage).

Bill McKeown