Gears can be eccentricity. eccentricity is caused due to the gear teeth profile. All gear teeth cannot be manufactured accurately with proper dimension.
They can be ± 0.5 mm. So due  to this eccentricity happens. Eccentricity can cause vibrations.
A badly Eccentric tooth may cause abrupt gear failure. so the run out must be checked. Dial gauge is used for checking the rut out valve.
The Dial gauge Tip is inserted between the tooth and the gear is rotated tooth by tooth, The high eccentricity point will shoe high valve and its is noted.
The high run out reading also indicate that the bearing clearances have increased and must be replaced.
The problem in the bearing can be found out by run out inspection
Run out value < 0.2 mm for medium duty gears and 0.4 mm for heavy duty gears
