Scooter Oil

Two Stroke Oils

Since there is no oil pump in a traditional two stroke engine, two stroke oil is added to gasoline to lubricate the engine. The oil coats parts as the gasoline is drawn through to the combustion chamber, and is then burnt along with the fuel. This is where the typical "blue smoke" comes from and unfortunately the main reason legislation exists against two strokes.

There are two main types of two stroke oil on the markets: non-synthetic and synthetic oils. I hope to add to this page in the future with more info, but for the most part the only difference I have seen on standard motors using synthetic vs. non-synthetic is that the inside of the motor and piston area is much cleaner after many miles using synthetic. Any comments on this would be appreciated.

Crankcase Oils

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.

For more than you ever wanted to know about oil click here.

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.

SYNTHETICS IN THE USA. @1996 rewrite ~2000©

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). Motul® uses esters in its products. Esters are mostly made of vegetables, minerals, and animal fatty acids. Motul’s® 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.

  1. Lube the engine.
  2. Lube the transmission.
  3. Lube the clutch.

A car with a manual 5 speed transmission has three different compartments, using two different oils to do the same job:

  • Motorcycles, especially air or oil cooled designs need lubricants that can handle higher running temps to increase viscosity retention, while reducing consumption and oil film breakdown. Especially since the capacity of oil is only 1 to 4 quarts.
  • Motorcycles use a constant mesh gearbox that shares the engine oil. Because of this, Motul® adds more medium extreme pressure (EP) additives such as zinc and a strong EP additive, called a sulfurized ester to handle the shear / meshing of the constant mesh gearbox.

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 a balanced friction modifier package. So that the wet clutch functions properly, ring seal stays strong and roller bearings roll and do not slide and flatten.
  • Super slick oils (energy conserving II type) are not recommended for today’s high powered motorcycles. Clutches will not engage correctly and will take longer to engage or slip and chatter when placed under heavy stress. (i.e. racing, passenger, trailer, uphill) also the plates will glaze up from burning/slipping.
  • Too much friction reduction will hurt your engine. Rings will skate instead of seal, reducing compression and performance.
  • Roller bearings will not roll, but slide causing flattened pins.
  • NOTE: The sulfurized ester is a part of this friction reduction package due to it’s ability to stick to engine parts (non- ferrous metals)

Motorcycles need strong anti-acid known as a base (TBN: total base number).

  • The steam that you see coming out of your tail pipe in the morning is condensation, which is a natural by-product of combustion in an engine. This condensation, which is acidic water, passes by the rings under compression into the crankcase and mixes with the sulfur, sulfuric acid is created. Anti-acid (base) neutralizes the acid before it can cause any damage.

Motorcycles need strong antl-foam additives to handle the design of the motor.

  • Motorcycles usually run at higher rpm’s than cars which aerates the oil more.
  • Motorcycles have more internal moving parts in the crankcase than cars do, foaming up the oil (engine-clutch-clutch basket, gears, shift drum, shift forks).
  • Motorcycles lean into turns, which may cause the clutch basket and gears to dip into the oil which causes excessive foam similar to whisking egg whites in a high speed mixer.

We must pop the bubble before it causes damage! Why?

  • Foam is air, air is a better insulator then a transmitter of heat. It does not transmit heat from hot metal parts to the oil very well or vice versa.
  • Problems – oil pumps do not pump air.
  • Oil pressure can drop!
  • TEMP’S can RISE due to inefficient heat exchange

Motorcycles need strong dispersants to suspend the clutch material and combustion by-products that are created and rubbed off during normal operations.

  • When you are waiting at a traffic light in gear or taking off from one. Where does the clutch material go? Right into the oil!!! We want the material to stay in small pieces and stay mixed in the oil, so that the oil filter can do it’s job. Otherwise the material will drop to the pan and collect in corners waiting for the day that you hit a wild bump and bounce back into circulation causing a clogged artery to anything it can. Just like a heart attack.

Motorcycles need a strong detergent, Why?

  • Because of more heat generation (more horsepower per cc than cars) trying to fry the oil onto the engine parts, and added dirt being dropped into the oil from the clutch and by-products from combustion.

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 Motul® 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.

2 Stroke Oil Mixing Calculator

A two stroke engine lubricates the piston, crank, and flywheel side bearing separately from the gearbox and clutch lubrication system. This is done by mixing a 2-stroke oil in with the gasoline.

As gasoline is drawn into crankcase, oil is deposited onto the various parts as well as being burnt in the combustion chamber (hence the famous 2-stroke blue haze). Older bikes had a much higher oil to gasoline ratio than the more recent bikes. Most Vespas made after 1980 and the Lambretta 75SL ' Cometa' have automatic oil metering devices with a separate oil tank. A mechanical system mixes the correct amount of gas and oil for the motor. Vespas with this feature can be identified by a conical sight glass which is visible just below the fuel tap lever.

Note: BE VERY CAREFUL. The wrong mixture can seriously affect your engine and can even result in a piston seizure. If you are unsure of what ratio your bike requires please find your model for the correct information. Older scooters usually take about 5% (20:1) - 6% (17:1) and newer scooters are usually 2% (50:1). I have also included 3% (32:1) because many tuned motors use this ratio.

Oil/gasoline mix required


Amount of gasoline as a decimal (i.e. 3.45) in units selected above

Lambretta Gearbox Oil Change

A two stroke engine lubricates itself in two separate ways. The gearbox, clutch, and drive is lubricated by standard gearbox oil. There is no oil pump. Instead, the gears running in the oil manage to pass enough oil around the gearbox to lubricate it properly. Gearbox oil in a scooter should be changed about every 3000 miles with new ST 90 gear oil, which is the same as SAE 30 motor oil. For some reason oil manufacturers have different viscosity definitions for motor oil vs. gear oil. This is a constant cause of confusion when buying transmission oil for your scooter. If in doubt remember that oil for car engines is crankcase oil and oil specifically for scooter transmissions is gear oil. Below are directions for any Lambretta series I through III.

Tools - You will need:

  • A 10mm allen wrench
  • Either an adjustable wrench, 21mm wrench, or a 21mm socket and driver
  • About 1 1/4 pints of ST 90 gear oil (SAE 30 motor oil) with a funnel or hose attachment to the container
  • Oil drain pan

It is a good idea to run the bike awhile so the oil will get hot and flow much more easily. Place the bike on its kick stand on level ground and remove the right hand panel. Find the lower of the two large allen head cover caps noted as (1) below on the chain case cover. Please note that the bike in the picture also has the rear right footboard removed but this is NOT necessary to change the oil.

Place an oil pan directly below the cap and unscrew it in an anti-clockwise direction to remove the plug. Be careful not to lose the small sealing washer around the outer rim as this can be reused if necessary, although it's best to replace it altogether. This plug also contains a small magnet which attracts any small metal pieces that are loose in the oil. It should be cleaned when removed.

The oil should immediately flow out until the gearbox is drained. Once drained, refit the oil drain plug and tighten carefully. The plug is only meant to seal against oil leaks so go easy! It is very easy to strip in the soft aluminum casing. If possible use a new felt washer to seal it rather than reusing the original.

Be sure the bike is relatively level and locate the second chain case allen head cap (2 in the photo above) and remove it. This second small hole is simply used to see when the gearbox is completely filled with about 1 1/4 pints (0.7 liters) of oil.

Find the filler hole and remove the large 21mm bolt with a domed cap and a small breathing hole. This is on the top of the chaincase near the main exhaust mount (see below).

I use an attachment that screws onto a standard quart size bottle of oil to fill up my bikes. I found it at my local Kragen auto parts store. It keeps things clean, is easy to use, and is relatively inexpensive. Start filling the gearbox until the oil reaches the upper sight hole.

Once this is done, refit the upper sight hole allen head cap bolt with a new felt washer and tighten down the filler bolt. Take the bike for a spin and once things get hot, make sure there are no leaks. Lastly, please dispose of your oil responsibly. It can be extremely harmful to the environment if simply dumped. Most recycling centers will take it for no charge.

Vespa Gearbox Oil Change

A two stroke engine lubricates itself in two separate ways. The gearbox, clutch, and drive is lubricated by standard gearbox oil. There is no oil pump but instead the gears running in the oil manage to pass enough oil around the gearbox to lubricate it properly. Gearbox oil in a Vespa scooter should be changed about every 3000 miles with new SAE 80 gear oil, which is the same as SAE 30 motor oil. For some reason oil manufacturers have different viscosity definitions for motor oil vs. gear oil. This is a constant cause of confusion when buying transmission oil for your scooter. If in doubt remember that oil for car engines is crankcase oil and oil specifically for scooter transmissions is gear oil.. Below are directions for most large frame Vespas. These instructions generally apply to small frames Vespas as well but the filler and drain holes are in different locations.

Tools - You will need:

  • A 10mm wrench or socket and driver
  • Large flathead screwdriver
  • About 1 1/4 pints of ST 90 gear oil (SAE 30 motor oil) with a syringe or hose attachment to the container
  • Oil drain pan

It is a good idea to run the bike around for a while to get the oil hot as it will flow much more easily. Place the bike on its kick stand on level ground and look underneath the right hand side of the engine. You'll see a small bolt that (if it is not covered in grime) should have OLIO printed on the head. Below is a shot of the oil drain bolt location on a large frame.

Place an oil drain pan below the bolt and loosen it allowing the oil to drain. Be careful not to lose the small sealing washer around the outer rim as this can be reused if necessary although it is best if replaced. Once the oil plug is removed the oil will flow out of the crankcase into the oil pan below.

Once all the oil has drained out, refit the oil drain plug, but only turn it about 1/2 to 1 turn past finger tight. Once the oil has drained refit the drain plug with a new felt or brass sealing washer. DO NOT tighten more than about a 1/2 to 3/4 of a turn more than hand tight. The small diameter and soft aluminum casing make it easy to strip the threads. If you find that the threads are stripped or you strip them yourself I have had success with using white plumbers tape around the threads. It can be bought at any hardware store and is basically a very thin plastic tape that plumbers use to seal threads when connecting gas or water lines. Wrap a 2" length around the threads and carefully tighten it in place.

Find the oil filler hole which is just to the rear and slightly below the gear selector box. Remove the slotted bolt with a large screwdriver. The new oil goes in this hole and needs to be filled up to the filler hole level when the bike is on the stand on level ground. I use an attachment tube which screws on to a standard quart of oil. These are available at most auto parts stores.

The shot below shows the oil just at the filler hole level, (and a little dribbling out. Refit the oil filler screw/bolt and double check you are not getting any leaks from the oil drain plug below. Auto parts stores will take your old oil for recycling and should not charge you for it. Most recycling centers will take it for no charge and it really does mess things up if you just dump it.

The oil drain hole is located just under the lowest point of the casing on a small frame Vespa.

The filler hole is located just below the rear shock mount on a small frame.

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