LO 7-9 Outline diagnostic techniques used for evaluating the condition of a piston ring-to-cylinder wall seal

1.7. Ring Break-In

Ring Break-In
When piston rings are initially installed with a new crosshatch finish on the cylinder walls, the rings will need to seat, or slightly wear, into the cylinder wall and conform to wall irregularities. A time period, called the break-in period , is needed to seat rings as well as other engine parts, including bearings, valve guides, piston pins, cam bushings, and other moving parts. During the break-in period, crosshatch is slightly worn away to conform to the shape of the piston rings, enabling the rings to seat better on the cylinder wall. It is important to operate the engine under heavy load for a short time after an engine is overhauled to seat rings and prevent formation of cylinder glaze in the engine. Under load, the cylinder gas pressure will push the rings against the cylinder wall hardest, which best helps rings to seat. This procedure is important, especially during the initial break-in period. Manufacturers will often provide a schedule in their service manuals that outlines specific break-in procedures, including what percentage of load to place the engine under for a prescribed amount of time.