When it comes to liner technology, the temptation is always to think in terms of cast iron - whether it be grey cast iron or one of the more recent ductile - or aluminium. Each takes its lead from the cylinder block supporting them and therefore, for reasons of thermal expansion, sound engineering sense seems to suggest that we stick to the same generic material.
There are exceptions though. Hypereutectic aluminium alloys (aluminium alloys containing more than 12 % silicon) for instance can be used successfully in cast-iron blocks where the lower rate of expansion is comparable, and of course cast-iron liners can be used successfully in aluminium blocks. But there is one material that is regularly used in many engines, particularly diesels, and which is only seldom used in competition engines - steel. Read more…
Last time we looked at ways of producing high-quality cylinder bores. Needless to say, the thinking and methods used might seem extreme to some or insufficient to others. In all this, however, we must always remember that it is not the shape or degree of roundness of the bore that is necessarily important but the degree to which the piston can conform and seal the combustion gases that is perhaps more critical. We can make the bore as circular in cross-section as possible but unless the piston rings used can conform to that shape, little will be gained. 
Spare a thought for the poor cylinder liner. As well as expecting it to be perfectly round from the outset, we then go on to expect it to remain so throughout the rest of its life, and under the most arduous conditions.
With a greater emphasis on waste and recycling in our private lives, is it no wonder that the ethos is now beginning to spill over into the world of competition. While once engine component parts might have been discarded in favour of new replacements, today, where possible, they may be reclaimed to race another day. No better example of this is the re-plating of aluminium motorcycle engine barrels; particularly those that tend to suffer most distress - those of two-stroke engines.
It is a rather strange but ironic fact of life that once a racing engine gets over a certain age then the biggest causes of failure are not likely to be those associated with excessive loads or the breakdown of lubrication, but simply that of corrosion. In the prime of its often very short racing life, an engine may be cosseted by professionals whose whole existence is centred on the well-being of that unit. It will be stripped, cleaned and examined on a regular basis and then re-assembled with the utmost care and then crated away into storage perfectly preserved until the time comes for it to be active again and give its best.
As an engineer and a power unit engineer at that, many might say that I have little need of a dictionary. And in truth, since the vocabulary of engineering terms tends to be so exact and rarely found in all but the most comprehensive of lexicological texts, for very many years I have simply done without. But it was while thumbing the latest version of the OED (Oxford English Dictionary) - the concise version I hasten to add, and a present given to me only recently, when I came across the word ‘Siamese.’ Defined as ‘a native of Siam (now Thailand) or an old fashioned word for Thai, 
A motorcycle engine, indeed any engine running at over 10,000 rpm, presents a particularly difficult challenge to the surface of its cylinder bore. The amount of heat flux and the limited time to dissipate it through the cylinder wall and into the coolant, will inevitably lead to high running temperatures and all of its associated problems. Although lightweight aluminium cylinders have been used to assist with the heat transfer, to minimise durability issues, thin steel liners have often been inserted against the inner wall to reduce the piston ring friction, give some level of acceptable durability and avoid engine seizure.
The surface condition of the cylinder bore has occupied the minds of motorists, engineers and enthusiasts for many years. Often expressed in terms of oil consumption – miles per litre or miles per quart depending upon which side of the Atlantic you reside – provided consumption isn’t excessive, all is generally thought to be fine. In a racing engine however, where cost of ownership is, let’s face it, more or less irrelevant, the real issue here is one of friction.
Although cast iron cylinder liners have always been a safe and reliable choice, the differential expansion rate between them and the aluminium pistons, as well as their shear weight, has always encouraged designers to look for better alternatives. When cylinder blocks were cast iron, engines were so heavy as to make any change in the cylinder liner material utterly futile but as demands for lighter engines made aluminium more attractive, the push towards some kind of aluminium cylinder liner was only to be expected. 
It is a fact not appreciated by many, except the specialists, but the technology of the cylinder bore surface finish has changed significantly over the years. While oil consumption was perhaps the greatest driver in the past, the push to achieve even less and less exhaust emission at higher and higher mileages, has caused OE engine manufacturers to focus even greater resources into getting the surface finish of the cylinder bore exactly right. And while, to the OEM this means emissions approval, to the racing industry this technology brings less friction and wear and with it, improved performance. 
