Technically, this scouring process is known as cavitation erosion. While it can appear anywhere on the cylinder liner, most pitting occurs as a narrow vertical band, perpendicular to the axis of the crankshaft. A secondary band may be found on the opposite side of the liner. The air bubbles are primarily the result of vibration of the liner wall as the piston travels up and down in the cylinder bore. Therefore, any change in the design of the engine which increases the vibration of the liner (such as thinner cylinder walls, longer sleeves or poor mechanical fit) will increase the potential for liner perforation. To combat the effect of cavitation erosion, all heavy-duty engine manufacturers recommend the use of SCAs. The SCAs coat the liner walls with a hard oxide film that acts as a barrier between the liner wall and the collapsing air bubbles, but does not significantly impede heat transfer. While the SCAs cannot prevent the formation or collapse of the bubbles, the oxide film is thick enough to keep the bubbles away from the liner surface, thus effectively preventing pitting of the liners.