Every single rotor needs to be balanced. It is often difficult to decide which particular balancing method to employ, rotational speed for balancing to be used, acceptable vibration level for balancing to be met, etc. Fortunately, there are some general guidelines for balance quality in rigid motor. Achieving close balance tolerances in rotors requires careful analysis of all factors that may introduce balance errors other than unbalance such as: damaged bearings, aerodynamics and hydrodynamic effects, misalignment, runouts, etc.
A suitable balancing criterion for the balancing quality would require the assembled machine to run smoothly. It is not an easy task to balance machines since there are many other factors than unbalance that contribute to uneven running of machines. In addition, there is no simple relation between rotor unbalance and vibration amplitude measured on the bearing housing. Many factors such as resonant frequencies, fits, environment conditions, etc may influence overall vibration levels considerably. Therefore, a measurement of the vibration amplitude will not indicate directly the magnitude of unbalance.
The Table shows balance quality adopted from ISO 1940. Balance quality grades are grouped according to the numbers with the prefix G. Balance quality requirement is different from one application to another. Fans, for example, require balance quality grade 6.3, G 6.3. The grade can be translated into residual unbalance by knowing the maximum service speed (RPM) and rotor weight, please refer to the Chart.
Patented XYO balancer is able to automatically reduce or eliminate vibration in rotating equipment. By implementing the XYO technology, balancing process can be eliminated. XYO balancer is also able to compensate for unbalance occurred during operation, thus no additional balancing during service is required.
| Balance Quality Grade | Type of Rotor |
| G 630 | Crankshaft drives of rigidly mounted large four-cycle engines; crankshaft drives of elastically mounted marine diesel engines. |
| G 250 | Crankshaft drives of rigidly mounted fast four-cylinder diesel engines. |
| G 100 | Crankshaft drives of fast diesel engines with six or more cylinders; complete engines (gasoline or diesel) for cars and trucks. |
| G 40 | Car wheels, wheel rims, wheel sets, driveshafts; crankshaft drives of elastically mounted fast four-cycle engine (gasoline or diesel) with six or more cylinders; crankshaft drives for engines of cars and trucks. |
| G 16 | Parts of agricultural machinery; individual components of engines (gasoline or diesel) for cars and trucks. |
| G 6.3 | Parts or process plant machines; marine main-turbine gears; centrifuge drums; fans; assembled aircraft gas-turbine rotors; fly wheels; pump impellers; machine-tool and general machinery parts; electrical armatures; paper machine rolls. |
| G 2.5 | Gas and steam turbines; rigid turbo-generator rotors; rotors; turbo-compressors; machine-tool drives; small electrical armatures; turbine-driven pumps. |
| G 1 | Tape recorder and phonograph drives; grinding-machine drives |
| G 0.4 | Spindles; disks; armatures of precision grinders; gyroscopes. |
