There have been many different types of piston ring developed over the years. Rectangular, taper face, barrel face, scraper, Napier, torsional twist, reversed torsional twist to name but a few. But one particular version that seems almost totally forgotten today, except for a few highly specialised applications is that of the Dykes ring. Peculiarly ‘L’-shaped in cross-section and named after it’s inventor not an embankment built to prevent flooding as might be at first thought, the Dykes ring was a regular feature on many a Read more…

The UN summit meeting in Copenhagen, COP 15, has come and gone. A meeting whereby 192 or so countries met together to fudge some kind of global agreement to reduce greenhouse gas emissions yet again attracted that section of the environmental lobbyists who seem to be determined to press their cause via mayhem and violence. It is little wonder therefore that the authorities seeking to maintain law and order, and according to journalist types, threw a ‘ring of steel’ around the venue to safeguard those present. The connotation to all this is clearly one of strength and Read more…

One of the most recent innovations in piston ring technology has been the invention of diamond-like-carbon coatings. The progressive move away from cast or ductile iron towards much stronger but less durable steel designs, made the development of suitable surface coatings a distinct priority.

Some time ago I had occasion to view the results of a study into engine friction. The engine, a quad-cam V8 of modern design and a ladder frame bottom-end, was motored in the fully hot condition up to 6000 rpm Read more…

I have to admit that at the moment, visits to our capital city are few and far between. The heart of business and finance maybe the place where many a motor sport deal is done, but the real action as far as I am concerned, is always in the workshop or on the track. But on those very occasional sojourns when needs must and when using the underground ‘tube’, I’m always reminded of one critical aspect of the piston ring. You see, at many of the stations when the train is just coming to a halt and doors open, the station announcer may call “mind the gap.” And lost in my own little world my mind immediately reverts Read more…

If the top compression ring has the most difficult of tasks in the engine then, at the other end of the piston ring pack, the oil control ring doesn’t have it much easier. Travelling at an average speed approaching 4000 feet per second or so, the component has to strip away any excess oil from the cylinder bore on the downward stroke and ensure just sufficient passes to lubricate the upper rings. The excess oil is then forced through the ring and drains back to the crankcase via a series of slots or holes in the piston. Read more…

Mention the subjects of durability and wear measurement in engine development and the image immediately conjured up is one of tests lasting hundreds of hours and lots of precise measurements, both before and after the test. When it comes to the piston ring we might want to check the ring gaps both free and as installed, measure the weight as accurately as we can, take a few harness measurements and visually examine the wearing surface. Apart from that there is little extra even the well-resourced development lab can do. Of course the rings may well be returned to the supplier for more Read more…

Selecting a suitable piston ring coating is, dare I say it, rather like choosing a wife. Selected in haste, the time could come when you repent at leisure and very much like choosing a mate, under times of great stress, the issue is one of compatibility.

It has long been acknowledged that the piston ring, particularly the top ring, has one of the most arduous tasks in the internal combustion engine. Having to seal the gap between the piston and bore from the passage of unwanted blow-bye gases, transfer huge amounts Read more…

Of all the components in a race engine, the top or compression ring has probably the hardest task. Although its primary purpose is to seal the combustion chamber from the crankcase below, this role is somewhat complicated by the requirement to dissipate the vast majority of the heat in the piston and to do so under the most trying of dynamic conditions. Positioned as close as possible to the top of the piston crown as is technically feasible, it is suggested that as much as 80% of the heat in the top of the piston, is conducted through this ring and into the cylinder wall.

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A piston can’t do a good job unless it has a good ring pack, and likewise, a good ring pack will be useless without a good piston.

Most people will appreciate that the piston ring exists principally to reduce the amount of combustible gases escaping into the crankcase, but I’m afraid there is a lot more to it than that simple statement. To start off with, the seal has to move at a speed of something up to 5000 ft per minute (26 m/sec) and cope with piston

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The piston rings in an engine serve to act as a seal to prevent the escape of fresh inlet charge and combustion products into the crankcase, and also to prevent an excess of crankcase oil from reaching the combustion chamber. As such they are an important component to consider in engine design. Poorly performing rings can lead to poor engine performance and increased oil consumption.

The general trend in piston ring design is towards lighter weight components and fewer of them. Read more…