Motorcycle Engine Oil - What you need to know

The lifeblood of a motorcycle, oil's the crucial fluid that keeps a motorcycle's engine ticking along nicely. It's worth knowing a thing or two about the most crucial part of your everyday ride.

Made up from a collective army of millions and millions of molecules, oil spends its days fighting friction, off-loading carbon and reducing heat within the fiery internals of a combustion engine. And to help us get a better understanding of what oil is and exactly what it does, we've asked and expert who has been working with oil for over 41 years and sells tens of thousands of liters of oil every year. If there's anything to know about oil, this guy knows it.

Oil is a lubricating product designed to prevent surfaces from rubbing together. Oil acts as a barrier between components keeping friction to a minimum. Without it, surfaces would overheat, wear and be susceptible to failure.

How often should people change motorcycle engine oil?

As frequently as possible. It's that simple. Yest, it is costly, but if you plan on keeping your motorcycle for a long period of time, it will save your money in the long term. And your motorcycle will perform better.
Oil is like blood, it works better clean and unadulterated. Something which people often don't realize is oil has a shelf life. Regardless of how little you've used your oil, if it's exceeded its shelf life it will be completely useless. When you buy new oil, remember to check for the shelf life of the oil on the container it comes in.

What's the difference between mineral, semi-synthetic and fully-synthetic oils?

Mineral oils are a basic refinement of the crude oil which comes out of the ground. Aside from anti-foaming additives to cope with the meshing from the gearbox and a detergent to stop unwanted carbon build up, they're pretty much free of additives.

Semi-synthetic oils are very similar to mineral oils, with the addition of a small amount of synthetic friction modifiers, which further reduce the friction created within an engine.

Fully-synthetic oils use a great deal more additives and a much greater amount of friction modifiers. Despite the suggestive name, fully-synthetic oil isn't a totally man-made product. The synthetic elements probably equate for 50% of the product's makeup. The synthetic polymers added to an oil's makeup depend on mineral oil to adhere to.

How are two-stroke oils different to four-stroke oils?

Just like two- and four-stroke engines are very different, the oils they use are equally very different. For a start, two-stroke oils have to be soluble in petrol. And then they have to be combustible too. The oil also has to be extremely heat tolerable with a wide operating heat range to cope with the nature of a two-stroke.
While one side of a two-stroke's cylinder is naturally hot, the exhaust port side is even hotter because of the returning exhaust gases. The variance in temperatures between the two sides of the cylinder is significantly different and the oil needs to be able to operate efficiently and effectively in both of the climates.

Another difference between the two is that two-strokes have sealed off gearboxes because of their dependence on crankcase pressure. That means they don't need the anti-foaming additive found in four-stroke engine oil.

Are oil detergents and additives necessary? What do they do?

Oil detergents haven't always been around, but neither have extremely high-performance engines. Just as engines have developed, oils have too. And modern engines are far more dependent on detergents and additives than older motorcycles, which typically revved at half or less of what you would rev a contemporary machine. Take carbon detergents for instance. They prevent carbon from building up within an engine, blocking the tiny oil-ways and requiring the need for an engine oil flush ever few thousand kilometers. They work by breaking down the carbon deposits, which then get carried and discarded by the oil at the oil filter.

Friction modifiers are another additive which improve engine life by reducing the amount of friction created within an engine. While these additives aren't necessary, they seriously aid both the performance and life of the motorcycle's oil, which in turn benefits the engine too.

Is it true some oils encourage clutch slip?

Yes. A lot of oils use synthetic friction modifiers, which encourage clutches to slip. The plastic polymers added to synthetic oils adhere to the clutch plates, filling the rough plate faces, encouraging them to slip. Motorcycle specific oils tend to use a man-made ester far as a friction modifier. It still benefits the engine in the same way as the artificial polymers, but the ester fat doesn't stick to the plates so there's no slip.

What are oil weights and why are they important?

Oil weights are the numbers listed on the oil's container denoting the viscosity of the fluid. Most modern oils are multi-grade, which means they have a different viscosity at different temperatures. 20/40 is probably one of the most common oils used in the motorcycle business, because it suits the Thai climate, the oil's solution will thin to a 20-weight solution, before thickening up to a 40-weight when the oil gets up to temperature. Before multi-grades were introduced you'd have to change the oil to suit the seasons.
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