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The Complete Guide

Piston rings are circular metal components that are placed around the piston of an internal combustion engine. 

They are designed to create a seal between the piston and the cylinder wall, thereby preventing leakage of combustion gases and ensuring efficient engine operation.

The primary functions of piston rings include:

1. Sealing: The piston rings create a tight seal between the piston and the cylinder wall to prevent the combustion gases from leaking into the crankcase and the lubricating oil from entering the combustion chamber.
2. Compression: Piston rings help maintain high pressure within the combustion chamber by sealing off the space above the piston. This ensures efficient combustion and maximizes engine power.
3. Heat transfer: Piston rings aid in transferring heat from the piston to the cylinder wall, allowing for efficient cooling of the piston and preventing overheating.

Piston rings are typically made of cast iron or steel and are precision-engineered to fit tightly against the cylinder wall. They are designed with various features such as grooves, chamfers, and coatings to enhance their sealing ability and reduce friction.

It's important to note that the exact design and characteristics of piston rings may vary depending on the specific engine and its requirements. Different types of engines, such as gasoline or diesel engines, may have variations in the composition and arrangement of piston rings.

COMPRESSOR RINGS / PRESSURE RINGS

The compression rings provide sealing above the piston and prevent the gas leakage from the combustion side. The compression rings are located in the first grooves of the piston.

However, this may differ according to the design of the engine. The primary function of these rings is to seal the combustion gases and transfer heat from the piston to the piston walls.

The oil is controlled by shearing the layer of the oil left by oil ring, thus providing the top compression rings enough lubrication. Moreover, it also provides help to the top compression ring in sealing and heat transfer.

WIPER RINGS

The wiper ring also called a Napier ring, or backup compression ring, are installed below the compression ring. 

Their main function is to clean the liner surface off the excess oil and to act as support back up ring on stopping any gas leakage further down which escaped the top compression ring. 

Most of the wiper rings have a taper angle face which is positioned toward the bottom to provide a wiping action as the piston moves toward the crankshaft.

If the wiper ring incorrectly installed with the tapered angle closest to the compression ring, it results in excessive oil consumption. This is caused by the wiper ring wiping excess oil toward the combustion chamber. 

OIL CONTROL / SCRAPPER RINGS

The oil control rings control the amount of lubricating oil passing up or down the cylinder walls. These rings are also used to spread the oil evenly around the circumference of the liner.

The oil is splashed onto the cylinder walls. These rings are also called scraper rings as they scrap the oil off the cylinder walls and send back to the crankcase.

These rings do not allow the oil to pass from the space between the face of the ring and the cylinder.

In the oil ring, holes or slots are cut into the radial centre of the ring which allows the excess oil to flow back to the reservoir.

Oil rings can be one-piece or two pieces. To increase the contact pressure between the ring and the liner surface, the rings can have chamfered edges on either the outer sides of the lands or facing the combustion chamber to reduce the oil consumption through improved oil scraping from the bore.