To diagnose rotor bar problems in vibration spectrum:
Identify actual running speed and subtract it from synchronous speed 1800-1775=25 rpm of slip, now multiply the slip rpm X the number of poles in the motor 4 poles x 25=100 cpm pole pass sidebands
IF the motor truly has a rotor bar problem, then you should see the pole pass sidebands around 1x 2x 3x 4x 4x 5x rpm or some combination of the harmonics. Keep in mind your bin spacing on spectrum, you must have good resolution to see these sidebands.
You should also see higher vibration at one time rpm and at one and two times rotor bar passing frequency, the motor will make an audible modulating growling noise, the motor will run hot, the motor will loose hp, the motor amps will constantly drift up and down, the speed of the motor will continually fluctuate.
MCSA data is valuable but these mechanical indications will also confirm the presence of broken rotor bars, these symptoms are present in copper bar or aluminum rotors
Hope this helps