LO 8-12 Identify and describe the purpose, types, composition, and failures of plain split insert bearings

Measuring Oil Clearances with Plastigauge ®

To evaluate the oil clearances of engine bearings, the use of Plastigauge ® is recommended. Plastigauge ® is a measuring tool consisting of a strip of oil-soluble plastic material and packaging printed with a thickness gauge.

Measuring bearing clearances with Plastigauge® is very simple when the engine is removed and turned upside down while on an engine stand. It cannot be performed in chassis when the crankshaft rests on the main bearing caps. After the main bearing cap has been removed from the inverted engine and the oil wiped from the crankshaft and bearing shell, a piece of Plastigauge ® is laid across the crankshaft journal. The bearing cap is reinstalled with a torque recommended by the engine manufacturer. When the bearing cap is tightened, the pressure causes the Plastigauge ® to be flattened. The less clearance there is, the greater the flattening and the wider it will be. When the bearing cap is removed, the width is measured by direct comparison with the graduated scale on the Plastigauge ® envelope Figure 88. The numbers on the graduated scale indicate bearing clearance in thousandths of an inch or millimeters on the reverse side of the paper gauge. Plastigauge ® is available in four different sizes and differentiated by four colors: red, green, yellow, and blue. Each color covers a particular bearing clearance range.

	A	B
	FIGURE 08-88: A. Plastigauging a main bearing journal. The Plastigauge ® is squeezed by the bearing and cap. B. Afterward, the width of the Plastigauge ® is compared against a gauge on the package.