The Development of Engine Oil


I suppose the need for lubricants began with the invention of the wheel. Suddenly, there was a need to keep the new wheels rotating on their axles. Water can be used to assist rotation as long as there is plenty of it; and all sorts of fats have been used over the ages.

Oil separates the rubbing surfaces of mechanisms by a hydrodynamic process; the relative movement of two surfaces creates a kind of 'wedge' of oil between them.

This main method of lubrication was augmented in the Twenties – oil carried within it as much as 2 percent by mass of sulphur. Under certain conditions, high pressure and heat, this served the unlikely purpose of providing extra lubrication by transforming into iron sulphide, visible as black deposits on rubbing surfaces. This is one of the first examples of dry lubrication, but the deposits rubbed away too easily and they became a contaminant in the oil.

The oil of choice for highly loaded machines and especially for bronze/steel bearings and gears, used to be castor based. The metals already worked well together and the oil combined effectively with both.
Its excellence as a lubricant is clear from the moment you feel it. R is very 'oily', as all oils are, but R seems to cling to the metal surface of cylinder bores, pistons, rings and bearings better than normal engine oil. This is because the ricinoleic fatty acid molecule is dipolar, i.e. it has a tiny electro-static charge difference end to end that attracts it to other molecules and to each other. The latter effect explains why R is thicker than other vegetable oils like rapeseed oil.

Besides providing a good lubricant the castor bean is used in medicines and cosmetics. Deep in thought, while working on my racing bikes in the Seventies, I would run my fingers through my hair. Could it really have been the Castrol R on my hands that has kept my black hair almost free of grey since? I am talking about a chemical process, not just a heavy build up of oil in my hand.

But the annual harvesting of thousands of tons of castor beans is potentially hazardous. Ricinus Communis, to use its proper name, is supposed to be the most poisonous plant on earth. Its evolution has given it a powerful protection against being eaten, the poison ricin in its outer skin. The valuable cator oil is in the kernel. The poison is valuable too, but only to cloak-and-dagger assassins with umbrella air-guns.

The trouble with R was that it did not deal well with getting very hot. Heat altered it irrevocable and it would turn into a sort of gum as it cooled down. It would also stain the interior of engines if left unused for some time. That meant the oil had to be drained from engines after races, particularly if you wanted to avoid piston rings getting gummed up in their grooves.

By the time I started using racing oil in my old cammy motorcycles it had become part-synthetic. The same chemicals that are used to prevent rubber from perishing were used to prevent oxidation and, thus, to increase its tolerance of high temperatures. Later, even better antioxidants developed for jet engines in the Fifties and Sixties were used.

It was discovered many years ago that Perspex-like polymers could control the thickness of oil, and prevent excessive high-temperature thinning. This gave birth to the multi-grade which has become the standard oil for most motoring uses and which mostly avoids the need to switch between oils for different seasons or types of motoring.

There have been huge advances in refining and in the development of additives that can improve the base properties of oil. And oil is now seen as an integral part of engine development – better engine design can reduce the need for additives.

But all of this progress, valuable as it is, ignores one thing. The smell of burnt oil. And in this respect Castrol R is unbeatable.
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