2582278 - 1028H PISTONS AND CONNECTING RODS
description of connecting rods
Any rod with joints at the two ends is thus defined.In the engine, the connecting rods connect the crankshaft and pistons. The part connected to the crankshaft, called the big end, has a rotary movement, while the upper end (small end) has a reciprocating rectilinear movement and is joined to the piston via the gudgeon pin.
COMPOSITION OF CONNECTING RODS
The connecting rods are made from spheroidal graphite cast iron. The gudgeon pins are the fixed type and are an interference fit in the connecting rod.The connecting rod consists of a body or shank, with a rectilinear axis, which rigidly connects the small end, fixed on the gudgeon pin; and the big end, fixed on the crankpin with bearings interposed.The big end is divided into two parts for fitting reasons: the fixed part is in one piece with the body and the moving part, called cap, is connected to the former by studs.As the connecting rod is subjected to compression and combined compressive and bending stresses, it tends to become deformed; consequently the connecting rod body must be made so as to combine light weight with maximum strength, and so it is constructed as a double T section.The connecting rod is the main connecting element between the piston and the crankshaft.DESCRIPTION OF PISTON
In the mechanism, called crank gear, which converts the rectilinear motion into rotary motion of the crankshaft, the piston slides reciprocally in the guide, called bore or cylinder.The top of the piston, or crown, contributes to determining the shape of the combustion chambers. - The part in contact with the cylinder is called skirt, and at the top, it has the grooves for housing the piston rings.As materials and production technologies are improving, the piston and oil scraper rings have now decreased, and it is likely that in the future they will decrease further.''Moreover, in racing engines they are already down to two''.
DESCRIPTION OF PISTON
The aluminium-silicon alloy pistons are graded into three sizes; to ensure correct assembly, an arrow is stamped on the crown to show the direction of rotation of the engine.
COMPOSITION OF PISTON
The piston consists of two parts:
- The head (1) or the area containing the piston rings, slightly smaller in diameter than the cylinder to allow for the thermal expansion of the metal.
- The skirt (2) or guide for the small end which supports the side thrust. The skirt contains two bosses for housing the gudgeon pin.
COMPOSITION OF PISTON
These pistons have a steel ring incorporated between the skirt and the head which has the task of preventing the expansion of the skirt in a transverse direction in relation to the gudgeon pin axis.PISTON OPERATION
This is the component which directly receives the engine impulse from the pressure of the combustion gas, via the connecting rod, and transmits the drive force to the crankshaft.It should meet to the following requirements:
- high mechanical resistance, which makes it possible to withstand the explosion pressures (~35 kg/cm2) and the dynamic stresses;
- high resistance to heat and wear;
- good thermal conductivity, to transmit heat from the hot area to the cold area underneath;
- light weight and extremely quiet operation, both when cold and when hot.
OIL JETS FOR COOLING THE PISTONS
The diagram below illustrates the position and operation of the oil jets for cooling the pistons.