Nitrogen is a colourless, tasteless, odourless, mainly diatomic gas that makes up about 78% of the air we breathe. Chemically it’s almost inert, and as well as being a critical part of human DNA it can also often be an essential part of the DNA make-up of a piston ring. For example, titanium nitride and chromium nitride are popular piston ring coatings. Applied to the bore-contacting outer surface of steel rings, such surfaces Read more…

The technology of the piston ring is evolutionary rather than revolutionary. Required to seal the gap between the piston and the cylinder wall, yet at the same time minimise the overall friction throughout the engine cycle at high temperatures and speeds of up to 4000 ft per second for long durations, if it works then don’t fix it.

Eventually, however, as engineers we will demand just that little bit extra - greater combustion pressures, Read more…

Numbers, I would dare to suggest, are the language of engineering. A true and simple enough statement but when used in an engineering context it can only describe the approximate size of things. In the purer forms of science and mathematics, numbers are precise. For instance, the atomic number of iron is precisely 55, or in the world of Euclidean geometry, pi, the ratio of the circumference of a circle to its diameter is exactly 22/7. Read more…

For all its apparent simplicity, your typical piston ring is a complex device. Required to seal against combustion gases on the power stroke and yet minimise friction on the upstroke, under all conditions of speeds and loads, the task might seem possible if we include the additional demand that all this and more should be achieved with the minimum of weight.

It is perhaps little wonder therefore that under the Read more…

The first decade of the 21st century will probably be remembered for when the benefits of surface coating technology really took off in the wider automotive industry. Although it’s something we have known in the performance engine world for a long time, the increased interest will no doubt spur companies into looking for even lower levels of friction and higher levels of durability, all in the name of improved carbon dioxide emissions. Read more…

If you think sealing the gap between the piston and cylinder bore of a conventional reciprocating engine presents something of a challenge, then spare a thought for the problems facing the Wankel engine. Once heralded as the rightful successor to the humble piston engine, the rotary Wankel unit gave a smoother power delivery in a more compact form, but early examples suffered greatly from combustion gas sealing issues between the rotor and its housing. And if you examine the dynamics of it all, you begin to see why. Read more…

Love them or loathe them, and despite being virtually outlawed in international motorcycle racing, two-stroke engines are still the main form of propulsion in the world of karting. With far fewer moving parts and power:weight ratios that most four-stroke engine designers can only dream about, the piston ring in a two-stroke engine has an altogether greater task than those in its four-stroke cousin. Not only does it have to seal the combustion chamber at much higher engine speeds and cope with an increased heat flow (one bang per revolution as opposed to one bang per two Read more…

After all this talk about the different types of piston rings - barrel, scraper, taper scraper and not forgetting of course the oil control ring - how do we assess their effectiveness and, perhaps more important, how do we know when things are starting to go wrong?

One way, I suppose, is to look behind you. If you see a slight blue haze in the rear view mirror then either you have a fancy tinted rear window or the beginnings of a major catastrophe. And should it be the latter, there is Read more…

It may sound obvious, but to assemble a piston ring into its grooves in a traditional two- or three-ring piston will require the ring to be split at some stage during manufacture. Placed on some form of mandrel and heat treated thereafter to an out-of-round set, once placed onto the piston and assembled in the cylinder, the theory is that it should exert a more or less constant pressure all the way around the bore.

Simple and yet highly effective, there are however two Read more…

Mention the word ‘Napier’ to many people and the chances are you will be met with a quizzical stare. To some, mainly engineers and scientists with an interest in history, they will talk of John Napier, the 16th century scholar and inventor of logarithms. To others, Napier is associated with rather large, industrial-type turbochargers or the classic range of multi-cylinder piston aero engines that were around just before the jet engine took over, such as the iconic Napier W12 Lion or the incredibly complex H 24 Sabre, both now considered Read more…