pistondrift

Pistondrift is a term used in mechanical engineering and automotive contexts to describe the unwanted drift or misalignment of a piston within its cylinder during operation. In Dutch-language sources, pistondrift denotes a small, gradual displacement of the piston from its ideal axis, which can arise from a combination of mechanical wear, thermal distortion, and lubrication conditions. It is distinct from piston slap, which refers to impact between the piston and cylinder wall, though the two phenomena can be related.

Causes include the wearing of piston skirts and rings, ovality or out-of-roundness of the cylinder bore, excessive piston-to-bore clearance, bearing wear, and unequal expansion of piston and bore due to overheating. Lubrication failures, poor oil quality, or improper oil pressure can exacerbate drift by allowing uneven force transmission.

Effects include increased friction and wear, higher oil consumption, reduced compression, degraded engine efficiency, and noise or vibration. In severe cases pistondrift can contribute to mechanical interference or reduced power output.

Diagnosis typically involves visual inspection with a borescope, measuring bore geometry, piston ring end-gap and skirt wear, and monitoring engine temperatures and oil pressure. Mitigation focuses on restoring correct clearances and alignment: ensuring proper bore roundness, correct piston-to-bore clearance, adequate lubrication, and effective cooling; selecting appropriate piston and ring materials and coatings; and addressing bearing wear or crankcase deformation.

Note: Pistondrift is not a universally standardized term and its exact definition can vary between sources.