Article: Engine Builders Are Moving To Thinner Rings—And Here’s Why

April 14, 2018

Jeff Smith April 09, 2018

The classic Hollywood line is you can’t be too rich or too thin. While full-figured starlets may now be finding favor in Tinseltown, the too-thin line is still in vogue when it comes to piston rings. It wasn’t all that long ago when state-of-the-art racing piston ring thicknesses hovered between 1/16-inch and 0.043-inch. The current state of production engines now employs ring thicknesses of 1mm and even down to 0.8mm. Since 1 mm equals 0.039-inch, that places a .08mm top ring at barely 0.031-inch. The benefits to thin rings are multifold and worthy of discussion.

The supporting mechanical reasons for this rush to be too thin are nearly universally beneficial. Let’s start with a discussion of how a ring actually seals to the cylinder wall. If you’ve ever assembled an engine, you know that piston rings need to be compressed slightly to fit into the cylinder and it requires a bit of effort to shove the piston down, especially if the piston is fitted with the old standard 5/64-inch ring package that was almost universally used for engines right up to roughly 20 years ago.

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