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Piston Coatings

coatingsDuring research for a forthcoming Race Engine Technology magazine article, Wayne Ward discussed the matter of coatings as applied to racing engine pistons with a number of the well-known suppliers, designers and manufacturers of racing pistons. The more specific point of polymer coatings in racing engines has been recently examined on the RET Monitor website, and the application of these to racing engine pistons was discussed. The focus of the discussion of polymer coatings on pistons was on the potential role that they can play in accelerated development of optimised skirt profiles. Our discussions with the piston manufacturers indeed confirmed that this is one of the reasons why this type of coating is currently being used.

In terms of coating ‘hard’ components, the new generation of coatings including TiN, TiCN and DLC are now very popular for racing use, and the application has begun to spread to high-volume series production road cars with a view to friction reduction and higher levels of efficiency. A number of people have been experimenting with DLC coatings on piston skirts for some years, with Formula One applications leading the way. Those Formula One engine manufacturers who had brought the technology to a sufficient level of maturity before having to homologate their engines are now able to reap the benefit of their early adoption of this technology. As with many new technologies, development of DLC coatings for pistons relied on these early adopters to bring about the possibility for more widespread use.

One of those companies who we spoke to is now in a position to offer DLC coated pistons to their customers, having developed the coating over a number of years. Cosworth, based in England, are involved in the supply of pistons for a wide variety of applications from tuned series production vehicles to Formula One. Discussing the matter of coatings with Cosworth’s Andy Pascoe and James Simester, they stated that the premium for DLC coatings is likely to be significant initially and that only part of the extra cost is due directly to the coating process. Development of the piston machining to accompany the coating has been a necessary part of the process, and the machining time on each piston is increased as a consequence. Having been able to examine a number of DLC coated pistons in recent years; the difference in machining is very noticeable in comparison with uncoated pistons.

However, the benefits are also significant, despite the extra cost. Asked about the increased efficiency of DLC coated pistons, Pascoe said, “Its coefficient of friction is excellent and outperforms everything else available currently,” before going on to state that, “it also achieves notable increases in piston life and peak power.” He further suggested that the coating enjoyed “unparalleled” wear resistance, presumably being part of the reason for increased piston life. Cosworth already plan to supply this to a number of teams racing in various championships in 2010 in both car and motorcycle applications.

So, the DLC coated piston is now available (albeit at a premium) to us all, and despite this extra price, may well work out less expensive due to increased piston life.

Written by Wayne Ward.

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