Ring sets in late-model engines are running hotter than ever before. As rings move up higher and higher on the piston to reduce emissions, they are exposed to more heat. A decade ago, the land width between the top ring groove and piston crown was typically 7.5 to 8.0 mm.
Adapted from Larry Carley's article in Underhood Service
The Extreme Life of Piston Rings and the Technology Used in their Development
Piston rings have one of the toughest jobs inside an engine. Theyre slammed up and down between the ring lands thousands of times a minute, theyre subjected to searing temperatures and extreme pressures, and theyre constantly scraping back and forth against the cylinder walls. In spite of all of this, the rings are expected to seal combustion and vacuum, prevent blowby, control oil consumption, keep the cylinder walls lubricated, cool the pistons, and last but certainly not least, last almost forever (150,000 miles plus in a passenger car/light truck engine or up to 1 million miles in a heavy-duty over-the-road diesel)!
Its a demanding list, yet most rings are up to the task and hold up pretty well assuming the right rings are used for the application, the cylinders are finished properly and the rings are installed on the pistons correctly. Obviously, the ring sealing requirements of a high-revving racing engine or a hard-working diesel engine are much more demanding than those of a mild stock engine. So with that in mind, lets look at some of the latest thinking as it applies to piston ring designs, materials and coatings.
Stock Rings With so many late-model engines running thinner, low-tension moly-faced ductile iron and steel rings, one might think cast iron rings are fading into histor...
