Piston Ring Fracture - Material Washout In The Piston Ring Zone

●Severe material washout reaching as far as the piston crown in the ring zone in the area of the first ring groove.

●Severe axial wear on the first ring groove.

●Severe mechanical damage on the piston crown.

●Running pattern of the piston skirt has a matt, buffed appearance.

Damage assessment

The damage is caused by the ingress of contamination into the combustion chamber. This is indicated by the severe axial wear on the grooves and on the first ring groove in particular. The contamination was then also deposited in the ring groove, where they caused abrasive wear on the piston ring and the ring groove. The axial clearance of the piston rings increased steadily as a result. In terms of its cross section, the piston ring was severely weakened, and it could no longer withstand the pressures of the combustion process and broke. Consequently, the broken-off part of the piston ring could move around practically unhindered in the rapidly enlarging groove. The washout shown in the picture was caused as a result of continuous “hammering” of this broken-off part. 

Possible causes 

●Severe axial wear on the ring groove and the piston rings caused by ingress of foreign bodies into the combustion chamber.

●If there is severe radial wear to the piston rings without any axial wear, then a likely cause is mixed friction wear as a result of fuel flooding.

●If there is no wear on the ring grooves or piston rings and the engine has only been run a short time after reconditioning, the problem is often caused by incorrect installation of the piston. 

●Ring flutter caused by excessive axial clearance of the piston rings. This is caused if only a new set of piston rings is installed during engine repairs, even though the ring grooves in the piston are already worn. 

●A piston that is unsuitable for the intended purpose.