What is the primary pitfall of a fixed center belt drive system?
The primary pitfall of a fixed center belt drive system is failure to consider the effects of system tolerance stack up on the belt tension. Belts and pulleys are manufactured to industry accepted production tolerances. Belt lengths and pulley pitch diameters are not perfect. In any large population there will be a distribution of values. There are also limits to the accuracy that the pulley distances can be maintained on a production basis due to machining tolerances.
Excessively low belt tension can be created when a relatively longer belt is installed on relatively smaller pulleys with relatively smaller spacing. Conversely, excessively high belt tension can be created when the reverse occurs. Such variations can cause timing belt tensions at installation to vary by 3X or more due to the stiffness of the belts which often have fiberglass reinforcement.
Excessively high belt tension bends shafts and journals, decreases bearing life, and decreases belt life. Excessively low belt tension can also decrease belt life as tooth engagement will be non-uniform and belt ratcheting may even occur.
Two Common Methods of Belt Tension Adjustment: