A Cross-Session Assessment of the 2X Response to Dial-Indicator-Verified Motor-Base Displacement: An Assembly-Related Transfer-Path Interpretation

The second rotational-frequency component (2X) is commonly used as a misalignment-related vibration feature, but its amplitude stability after reassembly remains uncertain. This exploratory study compares three independent normal-bearing reassembly sessions. Six horizontal motor-base displacement settings were imposed by an adjustment screw, rechecked using a dial indicator, and followed by three waveform acquisitions each. These settings are not direct measurements of shaft-center offset. Horizontal housing vibration was analyzed at twice a vibration-derived rotational-frequency estimate. The session-mean tracked-bin responses differed, but the inferred cross-setting trend showed sensitivity to the harmonic-amplitude estimator. A predefined nonlinear rotor–bearing–foundation model separately tested whether an equivalent support-state change alters transfer gain under controlled 20 Hz forcing. Within its parameter scan it changed gain and response sensitivity, without fitting sessions or reproducing their observed curve shapes. The three-session comparison is descriptive, and missing calibration and uncertainty records limit quantitative transfer. The findings motivate joint documentation of displacement setting, assembly, measurement conditions, and harmonic estimation before using absolute 2X amplitude across sessions.