Dirt

Intake of dirt in the engine is one of the most frequent reasons  for early wear on the engine and, consequently, also on the  piston rings. There are two principal causes of dirt damage:

The dirt is transported into the cylinder with the intake air. This  always happens when the air filter maintenance is not carried  out correctly. If the vehicle is driven without an air filter or if  there is a leak in the intake system and the dirt enters the  combustion chamber past the air filter. The dirt in the combustion  chamber also enters the piston ring grooves, where it combines  with the oil to form an abrasive paste. The height of the  piston rings is ground down in this case and the piston ring  grooves are expanded. The wear caused by the dirt on  the piston rings mainly acts on the ring sides in axial direction.  In radial direction (on the sliding surface), the ring also wears  due to the resulting mixed friction, but nowhere near as much  as on the sides. Roller marks on the ring sides are a frequent  indication of dirt in the ring grooves. The dirt, which consists  mainly of fine sand, in conjunction with the rotation of the rings  and the piston rocking motion, scratches characteristic patterns into the ring side.

Because the rings are mainly in contact with the bottom  groove side during operation, the wear mainly occurs on the top ring side. This is also where the roller marks are found .

The dirt is still in the oil circuit as a result of previous damage  and/or a poorly carried out repair/reconditioning. The dirt then  starts to wear on the cylinder walls and pistons from the  crankcase. Dirt particles also reach all bearing positions in the  engine via contaminated oil circuits. Although the oil is filtered  via the oil filter, the oil circuit is frequently not cleaned  correctly. Dirt that is already on the clean side of the oil circuit  reaches the bearing positions and results in premature wear or  damage.

In the event of engine damage, the oil filter is often so heavily  blocked through abrasion that the bypass valve opens. In this  case, the engine oil reaches the lubricating points unfiltered.  These facts are accepted in the engine design to prevent major  engine damage due to complete oil loss on the bearings.  Following engine damage, there are often still large amounts of  dirt in the oil cooler and in its oil lines. It is therefore irresponsible  to connect a new or reconditioned engine to an uncleaned oil  cooler and run the engine.