Vibration is monitored in a dual rotor engine. A first total vibration of the engine is measured during operation. Relative phase of the two rotors is then clocked, and a second total vibration of the engine is then measured during operation. First and second total unbalances are then resolved at a common response frequency from the measured total vibrations. First and second rotor unbalances are then resolved for the corresponding rotors from the first and second total unbalances. In a further method, corresponding corrective balance weights may be determined for offsetting the resolved rotor unbalances.