This study aims to investigate the influence of torque, rotational speed,
lubricating oil temperature, and main bearing clearance on the vibration signals
of diesel engine block surfaces, thereby establishing a foundation for
diagnosing abnormal main bearing wear conditions using engine block surface
vibration signals. An experimental test bench was constructed for a six-cylinder
diesel engine to collect vibration signals under varying rotational speeds,
torques, lubricant temperatures, and main bearing clearances. Frequency domain
analysis and wavelet packet decomposition were then performed. The frequency
domain analysis results indicate that the vibration signal amplitudes associated
with abnormal main bearing wear are primarily concentrated below 5 kHz.
Specifically, the energy in frequency bands below 1 kHz and around 2.5 kHz tends
to increase with higher rotational speed, torque, and main bearing clearance,
while the overall frequency domain amplitudes decrease with rising lubricant
temperature. The wavelet packet decomposition results reveal that the energy in
most decomposed frequency bands exhibits a positive correlation with rotational
speed, torque, and main bearing clearance, but a negative correlation with
lubricant temperature. Notably, the energy in wavelet packet bands 1–5 is
significantly affected by rotational speed, bands 1, 3, 4, and 5 are notably
influenced by torque, and bands 1 and 2 are strongly affected by main bearing
clearance. The findings of this study provide a theoretical foundation and data
support for the identification of abnormal wear states in the crankshaft–main
bearing system.