Piston normally comprises two components, the piston upper part (Piston Crown) and the piston lower part (Piston Skirt). The piston upper section includes the ring grooves for the compression rings. The connecting rod is held on the piston skirt by the piston pin / gudgeon pin. The piston pin / gudgeon pin is supported in the piston in a floating manner and axially fixed in position by retaining rings. The piston crown and skirt are connected to each other using undercut bolts.
Following are the component of a piston (MAN B&W Engine).
Piston Crown: Piston crown is the upper part of the piston and form the lower part of the combustion chamber. It taken the thrust created by combustion of fuel and transmit to the crankshaft through connecting rod. It contains groove for the piston rings.
Piston Skirt: Piston skirt made from aluminum alloy. The diameter normally higher than piston crown. It hold connecting rod head by piston pin or gudgeon pin.
Piston Rings: There are two types of piston rings. One is compression ring and other oil scraper ring. Compression rings sealing the piston to the cylinder liner to prevent blow by, oil scraper ring used to scrap lubrication oil from the cylinder liner. It prevent the oil getting into the combustion chamber. The running surface of the piston ring coated with Chrome-ceramic.
The piston rings must be replaced after the operating hours listed in the maintenance schedule. They are also to be replaced if, during intermediate checks, damage to the running surface is detected or there is too much clearance.
Piston Pin/Gudgeon Pin: The piston pin is supported in a floating manner and axially fixed in position with locking rings. The piston pin or gudgeon pin is normally a forged narrow hollow rod made of a steel alloy of high strength and hardness
Retaining Ring: Retaining hold the piston pin in position during the reciprocation motion of piston.
Other Components are: Guide shoe, Supporting ring and compression spring