3.7L 201CID OHV 12V V6 Engine Piston Ring Repair For Commander Cherokee Liberty JEEP

What is a piston ring

Located between the cylinder and the piston, piston rings are necessary components that allow the engine to operate efficiently.

1. Piston rings maintain gas compression between the piston and the cylinder wall.

2. Piston rings usually make necessary minimum lubricating oil film for preventing scuffing.

3. Piston rings transfer heat from the piston crown to the cylinder.

4. Piston rings prevent the piston from knocking on the cylinder wall.

Most automotive pistons have three rings: The top two while also controlling oil are primarily for compression sealing (compression rings); the lower ring is for controlling the supply of oil to the liner which lubricates the piston skirt and the compression rings (oil control rings). At least two piston rings are found on most piston and cylinder combination. Typical compression ring designs will have an essentially rectangular cross section or a keystone (right angled trapezoidal) cross section. The periphery will then have either a barrel profile (top compression rings) or a taper napier form (second compression rings or scraper rings). There are some taper faced top rings and on some old engines simple plain faced rings were used.

Lubrication of piston rings is difficult and has been a driving force to improvements in the quality of motor oil. The oil must survive high temperatures and harsh conditions with a high-speed sliding contact. Lubrication is particularly difficult as the rings have an oscillating motion rather than continuous rotation, as for a bearing journal. At the limits of piston movement, the ring stops and reverses direction. This disrupts the normal oil wedge effect of a hydrodynamic bearing, leading to pronounced wear and the formation of a 'step' in the cylinder bore around the height of the upper ring. Noting that some sleeve valve engines suffered far less from such wear, complex designs such as a rotating cylinder liner have been considered, just to address this problem.

Piston Rings critical quality

The piston might be a fairly loose fit in the cylinder. If it were a tight fit, it would expand as it got hot and might stick tight in the cylinder. If a piston sticks (seizes) it could cause serious damage to the engine. On the other hand, if there is too much clearance between the piston and cylinder walls, much of the pressure from the burning gasoline