Piston pin cylinders

The pistons in internal combustion engines are attached to connecting rods with cylindrical piston pins that are mounted in piston pin cylinders. A photo of a piston showing the piston pin cylinders is shown in Figure 1. Each piston pin cylinder has two cylindrical indentations on opposite sides of the cylinder to permit lubricant flow. This is shown in Figure 2. It is desired that the sliding cylinder surfaces be free of defects such as visible pores or scratches to reduce friction. IOMS laser scans can provide images of the cylinder surfaces to detect for defects. A laser scan of the surfaces of the cylinders is shown in Figure 3.

Figure 1. Piston showing piston pin cylinders for connecting the piston to its connecting rod

Figure 2. Cross section of a piston pin cylinder showing cylindrical indentations for lubricant flow

Figure 3. Image of piston pin cylinders

Both cylinders are measured in a single scan. The probe moves more quickly in the region between the cylinders to reduce measurement time and minimize the scan area that does not include the cylinders. The horizontal axis of the graph is angular position from 0 to 360 degrees. The vertical axis of the graph is depth in millimeters. Black areas are surfaces that are not perpendicular to the scanning beam. This includes the cylindrical indentations in each cylinder wall. The bright vertical lines are at the bottom of the indentations where the surface is perpendicular to the beam. Circumferential grooves in the cylinders show up as darker horizontal regions in the image.