184000255 - 1028H PISTONS AND CONNECTING RODS
CONSTRUCTION FEATURES
Connecting rods
The connecting rods are made from spheroid cast iron. The pins are the fixed type and are matched with the connecting rod.
COMPOSITION
The connecting rod consists of a body or shank, with a rectilinear axis, which rigidly connects the small end, fixed on the gudgeon pin with a copper alloy bush in between; 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. To ensure correct matching, the two parts are divided through fracturing. This technique combines simple construction with reduced production costs.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.PISTONS
The pistons are made from silicon aluminium alloy with a graphite coating on the skirt; the crown contains a letter indicating the grade and an arrow which, when the individual pistons are fitted in the appropriate cylinder, should be facing the direction of rotation of the engine (timing side).
COMPOSITION
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.
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 the following requirements:
- high mechanical resistance, which makes it possible to withstand the explosion pressures (approx. 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.