The secondary lubrication in a two stroke is done by transmission oil in the gearbox. All parts in the top end (piston, crank bearings, etc) that are inside the oil seal area are lubricated by oil mixed in the gasoline. Everything outside this area is lubricated by the transmission oil. The gears, axle bearings, and even the clutch are all lubricated by running in a bath of oil.
Transmission oil can also be synthetic or non-synthetic. Usually transmission oil for scooters is SAE 30W or ST90 which are basically the same thing.
Steve Lambert of First Kick scooters gave me the following information which was produced by Motul to educate people about their products. It is a very good introduction into different oil types and why they are necessary.
In the USA there are a few different types of synthetic base stocks used in engine oils. We will just touch on two in this technical / sales paper.
The word Synthetic is confusing; it describes a process, not a material. For example, White sand is synthesized into glass, but glass is never called "synthetic sand". Most people think that all synthetic oils are made of the same base, This is wrong! For most of the USA, there are mainly two types of synthetic oils (or as we like to say, synthetics are designer oils).
The most common is a PAO, short for poly-alpha-olefine, or easier to understand, it is synthesized petroleum oil. It is refined in a special process, or in simple words "synthesized". It still starts out by being pumped out of the ground. PAO’s are better than regular petroleum oil for handling heat, oxidation, low temperature startups and higher film strength. Drawback: PAO and petroleum are dynamic types of oil, you have to build up oil pressure and have rotation before a film is produced. Better said, you have to hydroplane the engine parts like you hydroplane a car in the rain, to create a film (or in the case of water-skiing, you have to build speed for the skier to get up and plane on the water). PAO’s are not very expensive because they are made from crude oil and produced in large quantities. You can usually tell when PAO’s are the main ingredient used as the cost of the 100% synthetic oil is less than $7.00 per quart.
The other main type of synthetics are synthetic esters, (diester, polyolesters, polyesters and complex esters). MotulŪ uses esters in its products. Esters are mostly made of vegetables, minerals, and animal fatty acids. Motul’sŪ esters contain a lot of coconut derivatives. Esters are much more expensive because the ingredients all have to be collected from natural resources and synthesized (a very expensive process) in smaller quantities. Esters have all the advantages of a PAO but more of them. Esters can handle heat better than PAO’s and when burned, esters leave far less coking deposits. Esters are static types of oils and are attracted to metal parts with an electro-chemical bond. This means no more metal to metal start ups. This also means that a film is there before the oil pressure light goes out preventing premature wear of high-stressed parts like cam lobes. The film created is up to 5 times stronger then petroleum oil.
The number one reason to run an ester synthetic oil is bond. The electro-chemical bond is made because the ester molecule is polar. Sort of like a refrigerator magnet. It is attracted to metal and sticks.The PAO molecules are neutral and act like a piece of plastic placed on the fridge. They just fall off. All commercial jet plane flying, use an ester synthetic of some type and not a PAO. You need to run an ester of some sort for maximum protection.
There are some companies calling level 3 petroleum base stocks synthetic. This oil is a good Petro oil. But it is not what we call a synthetic. The end result is that some oils are labeled incorrectly and are very inexpensive.
Let’s explain why handling higher running temps is important.With petroleum oils there is a much better risk of failure from volatility problems than with synthetics. Why?
Have you ever burned butter while cooking? Yes, everybody has burned butter! The running temp or maximum temp is low. When butter reaches its maximum running temp it starts to evaporate (volatility) then it carbonizes and then it sticks to the metal pan. Now compare butter to vegetable oil in which you deep fry french fries. The only way to heat vegetable oil so hot as to make it carbonize, you would almost need a direct flame.
Petroleum oil is like butter as far as handling heat! Synthetics are like vegetable oil - synthetics won’t burn up and stick to your engine parts or go out the breather as fast as petroleum oils will. Remember esthers leave almost no deposits if they do burn this is the second reason to run a synthetic oil. Because you’re not supposed to have extreme heat problems everyday.
Basic tech points: motorcycle oils vs. car oils
Most modern day motorcycles have one filler hole for the engine oil. The oil must do three jobs.
A car with a manual 5 speed transmission has three different compartments, using two different oils to do the same job:
EP additives come into play at the instant a medium extreme pressure’ is applied and high temperatures are created. Zinc lays down a barrier that prevents metal to metal contact and the sulfurized ester produces a sacrificial film that is destroyed during very strong extreme pressures as it prevents seizing. EP additives are generally corrosive especially those used in car gearboxes. We use this ester because it is far less corrosive and more environmentally safe than others that can do the job. This is what those TV advertised products forget to tell you when you see them test a ball bearing under 100,000 pounds of pressure.
To explain it easier, let’s take a sandwich wrapped in plastic wrap (the EP additive would be the plastic wrap). If you were to squeeze the sandwich you would contact the plastic wrap with your fingers (your fingers representing the gears) and the sandwich would squish, however, your fingers never actually made contact with the sandwich.
Motorcycles need strong anti-acid known as a base (TBN: total base number).
Motorcycles need strong antl-foam additives to handle the design of the motor.
We must pop the bubble before it causes damage! Why?
Motorcycles need strong dispersants to suspend the clutch material and combustion by-products that are created and rubbed off during normal operations.
Motorcycles need a strong detergent, Why?
Synthetics (now) can (if you cannot find your brand) be mixed with most high quality mineral, PAG or ester synthetic oils without major problems. Try to stay close to the viscosity range of the first oil. (I.e. 10w40 mixed with 10w40). We recommend an oil change when you get home from the "long" trip that consumed the oil, since the oil additive and base from the old oil is now not balanced.
These are some of the main issues that MotulŪ looks at when designing a motorcycle oil. As discussed earlier, synthetics can handle much higher running temperatures than conventional petroleum oils and can withstand more stress. Many people ask, so what! I don’t push my cycle that hard and I change oil every 1000 miles! I don’t need a $5.95 to $10.00 quart of oil in my bike. This is WRONG thinking ! The question we have for you folks is a simple one? Why do you wear a helmet? Gloves, boots, jacket and why do you buy insurance? In case of an accident! Right!! If within the first fifty (50) miles after an oil change, a rock hits your radiator or the thermostat sticks, the water pump stops pumping or whatever causes a major heat problem in your cooling system, what would you rather have in your engine? A mineral oil that acts like butter, that burns up and evaporates very quickly and also carbonizes OR an oil that can handle high running temps like synthetics (3250f to 3670f). High quality oils are insurance not only maintenance. Same is true about brake fluids and gear oils.
There are some new ratings from JASO, which is a group of engineers that decide what standards will be placed in effect to ensure proper performance for motorcycles. Motul has already several oils meeting these standards. The focus is on friction and clutches, EP and cleanliness.