Choosing measuring instruments for the fault detection of the main bearing supports of the YAMZ engine

Multiple factors determine the reliability in the engine repair, while an important criterion is the preservation of the geometric parameters of engine parts within the specified limits. The crankshaft bearing is a highly loaded unit in an engine. If the holes for the main bearing shells are worn or deformed, the shells may rotate, which will lead to failure and unscheduled repairs. The authors found out that measuring instruments typically recommended in the normative and technical documentation are assigned without regard to the tolerances of controlled quantities and have an error that significantly exceeds the permissible measurement error. The purpose of the work is to study the degree of influence of the measurement error on the dispersion zone of the dimensions of the mainbearing journals of the engine during fault detection. The authors have theoretically proven the criteria for choosing measuring instruments for monitoring holes for main bearing shells. The limit values of the permissible measurement errors and the errors of measuring instruments for monitoring wear or deformation of the holes for the liners of main bearings that are submitted for fault detection were also determined. The paper also considers the influence of the measurement error on the probability of errors when making a decision on the suitability of parts. When comparing the measuring instruments recommended for use by the engine repair manual, the number of incorrectly rejected parts is 6.9% more, and the number of incorrectly accepted parts is 3.5% more than when using a more accurate bore gauge with an error of ±3.5 microns. Reducing the error of measuring instruments will lead to a significant reduction in the number of incorrectly accepted and incorrectly rejected parts. This, in turn, will affect both the quality of the subsequent assembly of units, and the amount of external losses resulting from faulty parts.

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