LO 7-2 Classify pistons according to their application, design, construction features, and material

Trunk Pistons

Trunk pistons have a full skirt and are dimensionally longer than they are in diameter Figure 12. The full skirt design is stronger than a slipper skirt piston. This enables the cylinders to support higher cylinder pressures and accompanying side thrust. Side thrust is the force of a piston against the side of a cylinder wall produced by the angle of the connecting rod, which pushes the piston sideways when cylinder pressures are high. Cylinder pressure during the power stroke produces major side thrust while compression pressure produces minor side thrust. Trunk pistons are used in more rugged, high horsepower diesel engine applications and are almost always made from aluminum alloys. As trunk piston design has developed, pistons are being shortened to minimize cylinder wear, noise, mass, and friction as well as the likelihood that oil can be pumped into the combustion chamber Figure 13.

FIGURE 07-12: A trunk-type piston is longer than its diameter and has a full piston skirt.

FIGURE 07-13: The evolution of trunk pistons.