Seizure due to overheating centred around the piston head
DESCRIPTION OF THE DAMAGE
- Severe seizure starting from the piston head and lessening as it progresses towards the skirt end.
- Seizure marks are distributed around the entire circumference of the piston head.
- Surface of the seizure areas has a dark discolouration with severe scoring marks, and has broken up in places.
- Piston ring running surfaces show signs of seizure, which decrease in intensity towards the oil control ring.
DAMAGE ASSESSMENT
The piston head has been heated up so much as a result of extreme thermal overload that it has bridged the running clearance and destroyed the oil film. This caused a combination of seizure marks due to insufficient clearances and due to a lack of lubrication all around the piston head. A general lack of clearance due to insufficient piston installation clearance can be excluded as the possible cause, because in this case the damage would start in the skirt area (refer to the chapter entitled “Seizure due to insufficient clearance on the piston skirt”).
POSSIBLE CAUSES FOR THE DAMAGE
- Extended high loads during the running-in phase of the engine.
- Overheating due to faults in the combustion process.
- Malfunctions in the engine cooling system.
- Malfunctions in the oil supply (pistons with oil cooling or with oil cooling gallery).
- Bent or faulty oil injection nozzles, which insufficiently cool the piston with oil from underneath.
- Use of wrong sealing rings on the liner flange of wet cylinder liners (refer to the chapter entitled “Cavitation on cylinder liners”).