Aviation Training

Piston rings prevent leakage of gas pressure from the  combustion chamber and reduce to a minimum the seepage  of oil into the combustion chamber.  The rings  fit into the piston grooves but spring out to press against the  cylinder walls; when properly lubricated, the rings form an  effective gas seal. Piston Ring Construction  are made of high-grade cast iron  ground to  the cross-section desired. Then they are split so that they can  be slipped over the outside of the piston and into the ring  grooves that are machined in the piston wall.  Since their  purpose is to seal the clearance between the piston and the  cylinder wall, they must fit the cylinder wall snugly enough  to provide a gastight fit. They must exert equal pressure at  all points on the cylinder wall, and must make a gas tight fit  against the sides of the ring grooves. Gray cast iron is most often used in making piston rings....

Piston pin joins the piston to the connecting rod, machined in the form of a tube from a nickel steel alloy forging, casehardened and ground. Piston pin ( wrist pin )  used in modern aircraft  engines is the full-floating type, so called because the pin is  free to rotate in both the piston and in the connecting rod piston-pin bearing.  Piston pin must be held in place to  prevent the pin ends from scoring the cylinder walls.  A plug  of relatively soft aluminum in the pin end provides a good  bearing surface against the cylinder wall.

Piston is a cylindrical member which moves back and forth within a steel cylinder. The piston acts as a moving wall within the combustion chamber.  As the piston moves down in the cylinder, it draws in the fuel/air mixture. As it moves upward,  it compresses the charge, ignition occurs, and the expanding gases force the piston downward. This force is transmitted to the crankshaft through the connecting rod. On the return upward stroke, the piston forces the exhaust gases from the cylinder and the cycle repeats. Pistons are machined from aluminum alloy forgings. Grooves are machined in the outside surface of the piston to receive the piston rings, and cooling fins are provided on the inside of the piston for greater heat transfer to the engine oil. Pistons may be either the trunk type or the slipper type. T op of the piston , or head, may be flat, convex, or concave. Recesses may be machined in the piston head to prevent interference with the valves. Modern engines us...