In motor oils, synthetic and synthetic blend base stocks have increased in popularity over the past two decades. Synthetic oil is a different product from plain and refined oil. Synthetic oil is synthesized.
When crude oil is sifted at the time of refinement, you get the SAE30 base stock. This base stock you receive in the sifting process represents an average of different molecule sizes in mineral oil—some of them are larger than others. The sheering process that takes place when an engine runs, breaks down the oil molecules. The speed at which the big molecules are broken down in an engine is faster than that of the small ones. This reduces the average size of the molecules and thins the oil. Synthetic base stocks, on the other hand, are uniformly sized. Synthetic oils do not contain any waxes that block the low-temperature flow, nor instant-sludge crude oils or aromatics that vaporize quickly or drift away as soon as a spark plug fires nearby.
Good engine oil should be oily
Oil must be oily. It is meant for lubrication. Any liquid that is placed between a piston and its cylinder walls will reduce friction between them. Viscosity determines how much friction is reduced. Maple syrup and motor oils of almost identical viscosity don't lubricate equally. You can check this by rubbing some of each between your thumb and forefinger. If you have ever touched any car or bike engine oil, you will know how its viscosity differs from that of other viscous liquids. So, what is oiliness? This non-scientific term simply refers to the degree to which oil adheres to a surface.
However, if oiliness was the only thing to consider when choosing motor oils, we would extract all our oil from castor beans. Castor oil is what was dominantly used in motor races. It is the oiliest of oils. Castor oil is still the best lubricant in many ways. However, it can oxidize too quickly, leaving behind gums and varnishes on piston rings that stick to them and foul spark plugs. Castor oil can glue the piston rings into their grooves, and then there will be varnish and gum all over the engine. Castor oil is great, but there are options that don't cause all the issues castor oil causes.
Castor oil is a mix of ricinoleic and triricinoleic. This, mixed with other fatty acids, is still one of the most effective lubricants for 2-stroke race engines. Castor oil sticks to a metal with such force that it is difficult to remove. Castor oil is a very effective film lubricant.
Oil forms a hydrodynamic seal between engine surfaces. This prevents pistons and bushing-type bearings from making contact with the metal it slides against. The oil is pulled between the piston and the cylinder wall or shaft by viscosity, which creates enough pressure in the system to work properly. A well-designed engine will almost completely prevent scrubbing contact.
Engine parts are protected only with film lubrication due to the dipolar nature of oil molecules. If you are looking for synthetic engine oil for bike, then it's important to choose it cautiously. It should serve your specific purpose.