Frequent oil changes using high quality oil is a good investment. It pays off to remember oil change interval is a manufacturer recommended maximum, and if the use is hard, the oil will break down sooner.
Out of all the motorcycle components engine is the most complicated, sensitive and expensive to repair. High nominal output and fast moving parts set high demands for lubrication, which in turn requires frequent servicing in order to maintain good working order.
Many modern motorcycles boast service intervals exceeding 10000 km, highest ones being 16000 km. You shouldn’t consider this a word of god for change intervals, and oil may well deteriorate sooner, if the conditions are not optimal. In fact, if the operating conditions are harder, it’s imperative you change oil at tighter intervals.
Oil starts deteriorating basically the instant it’s poured in an engine. While riding, the oil is subjected to mechanical and heat induced stress. As relative speeds between surfaces and absolute heat increase, also the stress to the oil is increased. The more uniform the oil’s molecules are, the higher stress it can withstand before shearing. Imagine having sand in one hand and gravel in the other. Sand is much more uniform, so it runs easily through your fingers. Gravel sticks to itself and your hand. This is basically the difference between true synthetic base oil and mineral base oil. True synthetics consist only of molecules of desired shape and side, whereas mineral-based consist of varied molecules – mind you, the better the refining, the better the base oil. Therefore true synthetics have lower internal friction, conduct heat better and stand higher pressures.
The more speed the oil sees between metal surfaces, the higher in the shearing – therefore the more revs the oil sees, the shorter the change intervals should be. Another point of mechanical shearing is in the gearbox, between the gears.
The temperature shear factor is higher, however. A mineral-based oil starts to break down at temperatures exceeding 105 °C. At about 125 °C, its life is shortened to mere hours. The best ester-based synthetics, however, last temperatures closing to 150 °C.
If you ride track or enduro, both of which are hard on the oil and engine, it is advisable to change the oil frequently regardless of the oil type. This way you’ll not only ensure you always have fresh oil, but also get to observe oil and filter for metal deposits, which may tell for instance about failing bearings, and save you from destroying your engine.
Choosing the oil is straightforward. Always prefer synthetic over mineral. Check the recommended viscosity grade from the manual. The grade is in a given format, say 10W-40. Basically this means certain grade of cold viscosity (10W) and viscosity at +100 °C (40). Here it’s worth to note that the two numbers aren’t related to each other, i.e. the oil’s viscosity isn’t “10” when cold and “40” when warm, they’re just arbitrary, non-interdependent figures describing the oil properties.
There are basically two categories of oil gradings relevant to motorcycles; the API Service Categories and the Japanese motorcycle manufacturer’s JASO. These, if applicable, you’ll also find in your motorcycle’s manual.
API grades are in Sx format, where x is a letter starting from A. Noteworthy here is that a later letter of the alphabet doesn’t necessarily mean better oil, just more modern oil. Due to emission control requirements, some useful additives, such as zinc, have been eliminated from more modern oils. If you are unsure, it’s better to follow manufacturer requirements to the letter, even though API say the more modern oils are compatible with old engines.
JASO grades were introduced, when the Japanese manufacturers felt the automotive-based API grading wasn’t suitable for motorcycles. The automotive manufacturers’ goal of better economy had introduced friction modifiers to the oils, and these weren’t compatible with motorcycles that used motor oil in gearbox and clutch as well. There are two basic categories, MA and MB, where MA (which is divided to MA1 and MA2) means oil with no friction modifiers and MB oil with friction modifiers. Most motorcycles with wet clutched require JASO MA specified oil.
Whereas the mentioned grades simply differentiate oil by their characteristics, a good measure of an oil’s quality is Viscosity Index (VI), which indicates the stability of viscosity in two temperatures, a grade of over 110 is considered very good. Some manufacturers also give a very useful HTHS number (High Temperature High Shearing). This is a test of viscosity’s stability in extreme conditions. A grade of over 3.5 is considered good.
The oil change procedure itself is straightforward. Typically stripping the bike down isn’t required.