Analysis of scooter engine piston damage

The causes of operational damage to the piston of a single-cylinder two-stroke internal combustion engine (ICE) of a scooter, made of a piston aluminum-silicon alloy by mold casting, were investigated. It was found that the AK21M2.5H2.5 type alloy has a dispersed eutectic structure (α+β-Si) with a small number of primary silicon crystals of a compact shape, the size of which does not exceed 10 μm. The porosity of the cast alloy of the piston is less than the lowest 1st porosity point, as well as the quality structure, could not be the cause of its damage. The average value of the microhardness measured on the surface of the piston head (70 HV0.98) is slightly less than the standardized hardness (90 НВ ÷ 100 НВ) of ingots after mold casting and artificial aging without preliminary hardening, which indirectly indicates overheating of the piston during operation. The detected damage to the outer surface of the piston in the form of deep scratches and worn stripes is not caused by metallurgical or technological factors, but by violations of operating conditions: overheating and lack of lubricant in the contact zone of the piston and cylinder.