When a pump is new, clearance between the shaft and bearing is within .002 - .003 inches. This is the thickness of an average human hair. More clearance than this introduces the wear conditions described in the paragraph above. Severe wear between gear teeth and gear chamber, and bearing wear causes a pump to lose its ability to generate pressures and lift. Extreme noise and high power consumption are also symptoms.
Gear teeth wear occurs on the pressure face of each tooth only.
The extent of wear can be approximated by visualizing the tooth profile on the back face transposed to the pressure face. Wear can cause noise, loss of pumping, priming, or lift ability. Wear is observed by noting the level of the gear face below the flange surface. The shaft of a pump with a sheared pin can be rotated but will have absolutely no pumping ability, since the gears are not turning. Use size and number of pins as evident on damaged parts.