The cylinder forms a part of the  chamber in which the fuel is  compressed and burned. The crankshaft and connecting rod change the straight line  motion of the piston to a rotary turning motion. The crankshaft  in an aircraft engine also  absorbs the  power or work from all the cylinders and transfers it to the propeller. An intake valve is needed to let  the fuel/air into the cylinder. The piston, moving within the cylinder, forms one of the walls  of the combustin chamber. The piston has rings which seal  the gases in the  cylinder, preventing  any loss of power  around the sides of  the piston. The connecting rod forms a link between the piston and  the crankshaft. Spark plug An exhaust valve is needed  to let the exhaust gases out. Crankcase Figure 1-4. Basic parts of a reciprocating engine.  of cap screws, bolts, or studs. These accurately machined  surfaces are frequently referred to as cylinder pads. must have sufficient stiffness to withstand these bending  moments without major deflections.  [Figure 1-5] If the propeller is driven by reduction gearing (gears that slow  down the speed of the propeller less than the engine), more  area is required to house the reduction gears. A tapered nose  If the engine is equipped with a propeller reduction gear, the  front or drive end is subjected to additional forces. In addition  to the thrust forces developed by the propeller under high  power output, there are severe centrifugal and gyroscopic  forces applied to the crankcase due to sudden changes in the  direction of flight, such as those occurring during maneuvers  of the airplane. Gyroscopic forces are particularly severe  when a heavy propeller is installed. To absorb centrifugal  loads, a large centrifugal bearing is used in the nose section. The shape of the nose or front of the crankcase section  varies considerably. In general, it is either tapered or round.  Depending upon the type of reciprocating engine, the nose or  front area of the crankcase varies somewhat. If the propeller  is driven directly by the crankshaft, less area is needed for  this component of the engine. The crankcases used on engines  having opposed or inline cylinder arrangements vary in form  for the different types of engines, but in general they are  approximately cylindrical. One or more sides are surfaced to  serve as a base to which the cylinders are attached by means  Figure 1-5. The crankcase. 1-6