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When motorcyclists discuss engine oil, they quickly polarize into two groups. There are those who think all oils are basically the same, and that anyone spending more for premium oils is wasting his money, and there are those who feel there is a difference and are willing to spend the money to get the best product available. However, both groups share a lack of scientific information allowing them to make an informed decision. To offer some insight into this heated topic and help you determine which oil is right for you, we've decided to delve into this outwardly simple-but very complex-product. In Part One of this two-part series, we'll dissect the real what, how and whys of motor oil.

The first thing you need to know about motor oil is what it does for your engine. Motor oil actually has several purposes, some of which may surprise you. Obviously, lubrication is the main purpose. The oil serves as a layer of protection between the moving parts, just like shaving gel does between your skin and a razor.

However, oil also acts as a dispersant, which means it holds damaging stuff like dirt and metal particles suspended in the oil (rather than letting them settle to the bottom of the oil pan where they can be recirculated through the engine) so they can be removed by the oil filter. Then there is the job of corrosion retardant. By reacting with the nasty acids created by combustion, oil actually prevents these byproducts from damaging the internals of the engine. For instance, when combustion takes place, sulfur molecules in gasoline occasionally combine with air and water molecules, forming a vile brew called sulfuric acid. Left unchecked, this acid will eat away at internal engine compounds. Good oils, however, contain enough of the right additives like calcium, boron or magnesium to neutralize these acids.

Cooling is another important factor. Oil serves to cool hot spots inside an engine that regular coolant passages cannot reach. Since coolant usually only deals with the hottest parts of the engine, like the cylinders and cylinder head, there are many internal engine components that depend on oil for cooling as well as lubrication. For example, the transmission and clutch rely heavily on oil to regulate temperatures, since excessive heat expansion can change tolerances and cause clearance-related problems. Another area that uses oil for cooling purposes is the undersides of the pistons; with pistons becoming thinner for less weight, yet dealing with ever-increasing compression ratios, keeping the piston assembly cool is vitally important. Parts such as these can expose oil to extreme temperatures, so this is one reason that thermal stability is so important for motorcycle engines. We will do a specific test in Part Two to predict the oils' ability to survive in extreme heat.

The rest of the article is here
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