Piston ring fractures

Piston ring fractures are caused either by excessive wear, ring flutter or faults during ring mounting.

Fractures during operation of the piston rings do not occur without extreme operating conditions. When pulling the rings on to the piston, the mechanical stress is much higher than during operation. When pulling on the piston rings, the piston rings must withstand significantly more bending stress than during installation in the cylinder. A ring with joint or material  faults would break when pulling it on.

If broken piston rings are found in the engine immediately after a piston repair, they were usually damaged or broken beforehand by incorrect piston installation or faulty fitting  tools.

Rings can break during operation after a long service life. This happens if the radial or axial wall thickness has already been reduced significantly due to wear.

The significantly increased ring height clearance usually results in ring flutter, and the ring can no longer withstand the stress acting on it. The ring usually breaks into many small pieces.

But rings don’t necessarily have to have a reduced material thickness to break. If combustion faults occur during operation, rings may break due to the high stress without them being worn. Unintentional water or oil ingress in the combustion chamber can also lead to ring fractures. Liquids can not be compressed. If the quantity of liquid exceeds the volume of the compression space, the liquid must either push past the piston or break the piston or piston rings. The connecting rod may also bend or the cylinder wall/cylinder liner break.