3.3.8.1 Rotor Balance - Balance planes at each end of the rotor shall be readily accessible after removal of end covers or screen to allow field balancing of the generator without further disassembly. Balance planes shall incorporate some provision (such as a series of tapped holes) to facilitate the addition of balance weights. 3.3.9 Vibration - The degree of dynamic rotor unbalance shall not cause adverse vibration of Solar’s package. Vibration limits from rotor unbalance shall not exceed: