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Design features to improve top ring sealing

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Sometimes, when we run a new design of race engine, or have made a big change to one, we find we cannot get a good ring seal. Poor piston ring sealing can cause loss of performance through loss of combustion pressure and poor oil consumption – neither of which are desirable in a race engine. We can detect problems when we see high levels of blow-by on the dyno using our blow-by meter, or alternatively an unusually high rate of oil use. If this is an effect which is repeated over a...

The use of Spirolox clips for piston pin retention

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In most cases, piston pins are retained with some form of clip. There are occasions when people have preferred to use plastic buttons that can contact the cylinder bore, but these are really a niche product. Buttons were covered in a previous article. From motorcycles to freight trucks, for road transport and racing, circlips of one form or another reign supreme, at least in terms of numbers used. In many instances, piston pins are kept in their intended position with round-wire clips of...

Rotation of piston rings

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Piston rings lead a much more active life than might be thought. While we usually imagine that they only reciprocate in a motion defined by the piston, they also rotate during service. Such rotation has been the subject of many experiments and studies over the years, but this is not simply a matter of academic interest; there are implications for engine performance and efficiency. With few exceptions, race engines use piston rings of the conventional gapped type – that is, there is a...

Piston pins, surface treatments and coatings

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As discussed in previous RET-Monitor articles and in the pages of Race Engine Technology magazine, reducing the mass of a piston assembly is especially valuable because it then allows design engineers to reduce mass of all of the downstream components. The piston pin is a significant mass, and any reduction here allows weight to be removed from an optimised con rod and crankshaft. The temptation is to make piston pins smaller in every dimension – that is, outside diameter, inside...

New structural concepts

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There has been a great deal of evolution in piston design over the years, in which a large number of usually small development steps have given us some really beautiful components. If we are to describe a modern racing piston, we would probably be safe to say it is an aluminium component with a ‘slipper’ skirt, having ribs joining the piston pin bosses to each other and then to the relatively unsupported lateral areas of the crown. This is pretty much the state of the art at the...