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A radiotracer method was developed to measure real-time wear rates of piston rings and cylinder bores in spark-ignition engines. Initial work determined baseline wear rates during break-in and steady-state operating conditions. This work examines the effects of lubricant properties on wear rates of the ring/bore interface. Results show that engine oil service classification, the level of antiwear additives, severe engine aging, synthetic formulations, and viscosity classification have little or no impact on wear rates. These results suggest that concerns of wear between the rings and cylinder bore may not be a roadblock to extended oil-change intervals. Engine operation under cold temperatures appears to be a very important factor in ring/bore wear.

A radiotracer method has been developed to measure piston ring and cylinder bore wear rates in spark-ignition (SI) engines. The method has sufficient sensitivity to measure ring and bore wear rates in real time during normal operating conditions. This work reports measurements on the rates of break-in and steady-state wear of piston rings and cylinder bores during a variety of engine operating conditions. Results show that piston ring break-in is minimal and that ring wear rates are constant at steady-state engine operation. The key factor affecting ring wear is engine brake mean effective pressure (BMEP). Ring wear behavior is repeatable for a given engine type and between two different engine designs. Cylinder bore wear is dominated by initial break-in, cold-start wear, and changes in operating conditions. Wear of the cylinder bore during steady-state operating conditions is very low when compared to break-in and changes in conditions.

Radiometric wear measurement techniques have been applied to determine the effect of journal surface finish on journal bearing load capacity. Bearing load capacity was measured by using a test machine that applies a linearly increasing unidirectional load to a radioactive test bearing. The onset of bearing wear provides a direct measurement of fluid-film breakdown, which is used to define hydrodynamic bearing load capacity. By use of a journal that can be located at two different positions on the shaft, the relative difference in load capacity between two journal surface finishes can be measured without the need to disturb the geometry of the bearing. The effect of journal surface finish on bearing load capacity was thereby quantified. In this study, nodular iron journals were prepared to have test surfaces with different levels of surface roughness.

Excessive cylinder bore out-of-roundness (OOR) can adversely affect the sealing functionality and durability of the piston-ring pack in an engine. This work reports the effects of changes in cylinder bore OOR on: (i) the rotation of the top and second compression rings, and (ii) oil consumption in an open-deck 4.5-L V-8 engine. A method was devised for altering the level of OOR in one cylinder of the engine without engine disassembly. Radiometric techniques were then applied to measure both piston ring rotation and oil consumption of that cylinder at three different levels of bore distortion. Results of these measurements are of value in determining the range of acceptability of production specifications for cylinder bore OOR.

A radiometric method has been developed for the determination of camshaft wear during engine operation. After a radioactive tracer is induced at the tips of one or more cam lobes by the technique of surface layer activation, calibration procedure are performed to determine the amount of radioactive material remaining versus the depth worn. The decrease in γ-ray intensity measured external to the engine is then directly related to cam lobe wear. By incorporating a high-resolution detector and an internal radioactive standard,measurement accuracy better than ±0.2 μm at 95% confidence has been achieved. Without the requirement of engine disassembly, this method has provided unique measurements of break-in wear and wear as a function of operating conditions. Because this approach requires only low levels of radiation, it has significant potential applications in wear control.

A radiotracer technique has been developed to monitor the rotational movement of piston rings during engine operation. Each ring to be monitored is modified by incorporating two different radiotracers at an angular separation of ∼120°. After engine assembly, a high-resolution detector is mounted outside the engine block to measure the γ-ray emission rates of each of the isotopes. Gamma-ray intensities monitored during engine operation provide information to determine the angle of ring-gap orientation in real time. The radiotracer method for ring-rotation measurement can be applied to any ring in the engine and may be modified to monitor the simultaneous movement of two rings in a given cylinder. Because the radioactive sources are confined and are of low intensity, radiation safety precautions are minimal.