A type of crosshead piston is currently being used in some engines (fig. 4-11). The crosshead piston is a two-piece unit with a crown that can withstand the high heat and pressure of a turbocharged engine and a skirt specifically designed to absorb side thrust.

The crown and skirt are held together by the piston pin. The downward load on the crown pushes directly on the pin through a large slipper bearing (bushing). The separate skirt has less thermal distortion than the crown piece and is free of downward thrust loads. It specifically guides the piston in the cylinder, takes up side thrust, and carries the oil scraper rings. The crown carries the compression rings. Since the crown is

Figure 4-11.Typical crosshead piston and connecting rod components.

separate, it takes only a slight amount of side thrust and is not forced to slide sideways under the compression rings when they are pressed hard against the bottoms of their grooves by combustion gas pressure. Lubricating oil is fed upward by pressure to cool the piston pins and piston crown.