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Maintenance Motorcycle engine oil
Engine oil is one of the most important aspects for peak performance and engine longevity. The function of engine oil is multifactorial and includes more than just reducing friction of moving parts, particularly in four-stroke engines.
Functions of motorcycle engine oil
- Removes heat from four-cycle engines. As engine oil circulates between the engine parts and oil reservoir, its function is to continually cool the engine.
- Forms a seal between the piston rings and the cylinder wall. It ultimately helps to form a good seal in the subtle irregularities of metal parts.
- Acts as a cleaning agent. In four-cycle engines, motorcycle oil collects carbon and other debris from moving parts and carries them into the reservoir or oil pan for removal.
- Absorbs vibrations and shock between moving engine parts, it absorbs movement from rapid piston firing providing a cushioning effect
- Prevents metal-to metal wear, significantly reducing friction and wear of moving engine parts.
Understanding engine oil viscosity
Viscosity refers to the ability of a liquid to flow. Normally in winter, oil is thicker, and in summer it is thinner. An oil that has a low viscosity flows easily, and an oil with a high viscosity is thicker and flows more slowly. An analogy to help with understanding engine oil viscosity is the difference between syrup, such as honey, in colder temperatures, where it is solid, thick, and difficult to move, compared to the same honey in warmer temperatures, where it is free-flowing, or less viscous.
To help with rating viscosity, the Society of Automotive Engineers (SAE) has developed a grading system to give a numeral value to viscosity in winter conditions at -18°C (-0.4°F) and in summer conditions at 100°C (212°F). The lower the numerical value, the thinner the oil, and the higher the value, the thicker. Viscosity in Winter (W) is graded from 0W to 25W, and for warmer weather, the viscosity is rated from 20 to 60.
Therefore, in winter, engine oil needs to be slightly thinner to accommodate its tendency to become thicker, and in summer, slightly thicker to compensate for its tendency to thin out too much. In single viscosity oils, an engine oil rated SAE 10W is much thinner than an oil that is rated SAE 25W.
Many four-stroke engine oils have a multi-viscosity rating for enhanced versatility in both colder and warmer environments. For example, SAE 10W-50 means that the oil has an SAE rating of 10 in winter, meaning that it will have a low viscosity (act thinner) at lower temperatures and hold a higher viscosity (act thicker) when it gets hotter. In other words, this type of multi-viscosity oil can hold its thickness across a broad range of temperatures without over-thickening or thinning.
Engine oil and wet clutches
The Japanese Automotive Standards Organisation (JASO) developed a testing method to grade an oil’s ability to resist clutch slippage. Standard car oil often contains friction modifiers, which are not suitable for wet clutch systems found in motorcycles, and therefore different oils are needed for optimum performance in motorcycles.
JASO has two ratings for four-stroke motorcycle oil: JASO MA for motorcycles with a wet clutch and JASO MB for motorcycles fitted with an automatic transmission. There are then a further two subcategories under JASO MA, MA1 & MA2. The highest moving clutch friction performance is found in a MA2, with M1 providing slightly inferior friction modification.
Mineral, semi-synthetic, and full synthetic oils
Mineral oils are predominantly derived from unrefined fossil fuels or petroleum sourced from underground reservoirs beneath the earth’s surface. Petroleum undergoes intense refinement to produce base mineral oils, and additives such as zinc are added to improve the anti-wear properties. Good-quality refined mineral oils with additives can offer just as good protection as more expensive synthetic oils.
Semi-synthetic oils are a blend of both mineral base oils and synthetic oil. Most reputable brands will use a minimum of 20% synthetic oil in a semi-synthetic oil. This blend offers excellent protection and improved performance at a much lower price point than full synthetic oils.
Full synthetic oil is made from the refinement of base oils that have been synthetically altered in a lab to create an oil with a chemical structure that is more uniform and consistent. This improved uniformity creates an oil that has better lubricating properties, superior performance due to less friction, superior heat resistance, and excellent cold flow properties.
