If It Takes A Piston Ring, We Can Build It

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TECH ARTICLE

The History of Piston Rings

Nearly 25 years BEFORE Nicholas Otto invented the spark ignited internal combustion engine (the type of engine most cars use), an English Engineer by the name of John Ramsbottom invented the piston ring in 1852, and he did it for steam engines. So, before we had cars or gasoline, the industrial revolution brought us steam locomotives. Prior to Mr. Ramsbottom’s stroke of genius, steam engine pistons featured grooves packed with hemp or cotton to improve sealing. Of course, this didn’t work that well, which led to John Ramsbottom’s invention of the metallic, split ring design in1852. Over the next decade, he continued to refine his design, and eventually a steam engine could go 4,000 miles before needing to replace the piston rings. That was a significant improvement in performance and durability. 170 years later, the piston ring is still evolving and enabling greater engine performance and durability.

Interestingly, Britain is not only the birthplace of the piston ring, but it is also the home of several of advancements in piston ring design. English engine manufacturer D. Napier &Son is often credited for the invention of Keystone style top ring and eponymous Napier style 2ring. Both developments took place during the 1930’s, and these designs are commonly used today in diesel and gasoline engines respectively.

If that wasn’t enough, the UK is also home of the most advanced piston rings, which are found in Formula 1 engines. With over50% thermal efficiency, today’s F1 engines are the most efficient combustion engines ever built (rivaling combined cycle gas turbines). That’s nearly double the efficiency of a regular petrol engine and 50% better than a turbo diesel. The folks at Mercedes AMG made some videos about this achievement, which can be found on YouTube.

One of the reasons for the incredible efficiency of these engines lies in the fact that piston rings account for nearly 40% of all engine friction. That makes piston rings the number 1 source of friction in an engine, so the best way to improve engine performance and durability goes right back to Mr. Ramsbottom’s invention - the piston ring. The evolution of piston ring materials and coatings has allowed for innovation in piston ring sizes and designs. Today’s piston rings are dramatically thinner, lighter and stronger than your Grandfather’s piston rings.

For decades, cast iron was the material of choice for piston rings. However, the low hardness of grey cast iron, up to 22 Rockwell C, allowed for higher wear, which shorten engine life. The advent of hard Chrome plating allowed cast rings to achieve a face hardness of 72Rockwell C. These hard chrome rings lasted much longer, but were much tougher to break-in. This led to rougher cylinder bore finishes and many lubrication “tricks” that enabled the hard chrome faced rings to break-in.

By the 1960’s Plasma Moly rings appeared, which replaced the hard chrome face with a softer, porous moly face coating. The much softer Moly coating, 80 on the Rockwell B scale, did not require the rougher cylinder bore finishes or lubrication “tricks” to achieve proper break-in. However, the sprayed on “Moly” coating was susceptible to flaking in higher horsepower applications. Also, the cast iron or ductile iron base ring could only be so thin before they became too brittle.

As such, steel rings that feature PVD(chemically bonded) face coatings were developed in the early 2000’s, which allowed for thinner piston rings with greater strength than the iron forefathers.

With the advent of better piston ring materials and coatings, the potential performance of piston rings skyrocketed!

Because of the instant reduction in friction and increase in durability, professional racing teams quickly adopted the thinner, steel piston rings.

Here’s some real-world proof of that statement. Between my Dad’s 20 years in NASCAR as a driver and my15 years working for NASCAR teams, I’ve seen the evolution of piston rings firsthand. Back in 2001, the state-of-the-art piston ring package in NASCAR was an .043, .043, 3mm Ductile Moly set, and those rings lasted one 500-mile race. It was typical for the engine to be down5 to 8 HP after that one race. Today’s NASCAR engines use .5mm , .6mm, 2mm PVD coated steel rings that last over 1,500 race miles without losing a single horsepower!

It’s not just racing engines that take advantage of thin ring technology. OEMs around the world have embraced the efficiency of thinner piston rings. A 1972 Chevy V8 used a 5/64, 5/64, 3/16cast iron ring package. 50 years later, turbocharged, direct injection engines making twice the horsepower per cubic inch of that old Chevy utilize 1.2, 1.0,2.0mm steel rings.

More efficient piston rings increase horsepower, reduce engine temperature (both water temperature and oil temperature) and extends motor oil life. All of which means engine life and performance increase. I think John Ramsbottom would be proud to see today’s piston rings.