05 Here’s the high-pressure pump, disassembled. Inspect the pump shaft for wear, especially near the squared-off end where the lip of a rubber seal typically wears a groove. If there’s any question about the condition of the shaft, replace it. Also inspect the end plate (right) for circular patterns created by gear rotation. Lap the end plate on 600-grit sandpaper on a surface plate to remove wear due to gears. Unfortunately, replacement parts vary in quality, so it’s important to take note of small details. For instance, a replacement shaft should have a shiny finish, and be of exactly the right size. Even a shaft undersized by 0.001-inch can cause free-play, and allow the tips of the gear to hit the cavity walls.