Dry running damage due to lack of lubrication caused by fuel flooding

Unburned fuel has condensed at the cylinder running surface and diluted or washed off the load-bearing oil film. As a result, the interacting sliding parts (piston and cylinder bore) run dry against each other, which results in long, narrow friction marks. The piston ring zone usually remains undamaged.

NOTE In the case of damage caused by unburned fuel, the damage occurs at the load-bearing areas on the piston skirt. These are the points at which the normal wear pattern would have formed on an undamaged piston.

• Overrich engine operation and abnormal combustion caused by faults in the mixture preparation or in the ignition system.
• Insufficient compression and, as a result, incomplete combustion.
• Coldstart device defective or operated for too long(carburettor engines).
• Oil dilution caused by frequent shortdistance driving or an overly rich mixture.