In addition to the impeller, raw-water pumps contain other components that may require periodic service, repair, or replacement. The pump's cover plate and cam eventually wear out because of continuous abrasion. It's often hard to judge just how worn these components are until you compare them to their replacements. Because the wear is usually uniform and gradual, it's difficult to detect. Avoid having to make this determination by replacing both the cover plate and the cam with every third impeller replacement. Other pump components that can fail include seals, bearings, and shafts, all of which can be replaced. It's worth considering that unless the labor is yours and, thus, free, at some point it's less expensive and less aggravating to replace the pump in its entirety. Many cruisers choose to carry a complete spare pump that can be installed relatively quickly. The pump that's been removed can then be repaired or rebuilt over a cup of coffee or a margarita once you've dropped the hook in a protected anchorage.