On some but not all engines, the piston liner can be replaced if it becomes worn. The piston liner forms the space which allows the piston to slide up and down. Piston liners are subjected to constant movement during driving and operate in temperatures in excess of 2000 degrees Celsius. Therefore they can degrade and wear out over long periods of use. Replacement piston liners must be an exact fit for the specific vehicle engine.
Piston rings usually come in groups of three. Their role within a car engine is to form an airtight seal between the piston liner and the engine piston itself. Whilst a relatively small part, the piston ring is vital in keeping oil out of the engine cylinders and the fuel mix and combustion process inside.
Due to the extreme conditions in which they operate, piston rings can become worn or break entirely. They also must be replaced with quality piston rings if replacing the piston or the piston liner.