En route to the combustion chamber, the intake air passes a number of places where components are joined together (1). If there is a leak at these joints, the engine will draw in unfiltered, contaminated air. The same effect will be seen if intake air is insufficiently filtered.
Reasons for this include:
Neglecting air filter maintenance (exceeding change intervals)
Not maintaining sufficient levels of cleanliness when changing the air filter (dirt gets into the clean side)
Filter elements are faulty, deformed or degraded, or have become dislodged
Unsuitable or incorrect filter elements
Filter elements damaged by compressed air
Missing filter elements
Dirt that enters the combustion chamber with the intake air rapidly produces abrasive wear on the cylinder sliding surfaces, pistons and piston rings. Dirt also accumulates in the piston ring grooves and combines with the engine oil to form an abrasive paste.(2). Constant rotation of the piston rings means that they get worn away at the top and bottom and the piston ring grooves become enlarged (3).
Wear caused by dirt on the piston rings mainly occurs in the axial direction and at the top of the ring sides. In the radial direction (on the sliding surface), the piston rings also get worn by mixed friction. However, here the wear has less of an effect than on the sides of the ring. Wear at the top and bottom of the piston rings causes loss of tension and axial guidance of the piston rings. This causes problems with the seal between the pistons and cylinder bores.