Piston Ring Land
The raised metal sections between the piston ring grooves on the side of a piston.
Piston ring lands are the horizontal metal ridges on the outer circumference of a piston that separate the piston ring grooves. These lands support the piston rings structurally, keeping them flat and properly positioned as they seal the combustion chamber and scrape oil from the cylinder walls. The top ring land is subjected to the highest temperatures and combustion pressures in the engine.
Under extreme conditions, such as engine knocking (detonation), pre-ignition, or excessive boost pressure, the piston ring lands can crack or break off entirely. When a ring land breaks, the piston rings lose their support and can twist or snap. This leads to an immediate loss of cylinder compression, severe blow-by of combustion gases into the crankcase, and deep scoring of the cylinder walls.
Symptoms of broken ring lands include a sudden engine misfire, rough running, a heavy oil vapor smell from the crankcase breather, blue exhaust smoke, and low compression on the affected cylinder. Diagnostics involve performing a compression test and a cylinder leakdown test, which will show high air leakage into the oil pan. A broken ring land requires replacing the piston and honing the cylinder.