Why Does A 2 Stroke Engine Require Internal Oiling?

This thread is in connection to a message sent to me by CEan-mreccentric

Hi iishantopre,
I have a ques from many days....
Why 2 stroke engines require oil with petrol?
Can you pls give me the information with links about it?
and also why can't it run without internal oiling?
Lubrication is required for any engine to keep cool and also to keep wear and tear at bay. With this, I assume that everyone knows the importance of Lubrication.

Now as we all know in four stroke engine engine oil is made available to the vehicle separately while that in 2 stroke engine, add oil with fuel.

This is because the difference lies in how engines are lubricated.
In four stroke engine we have various types of lubricating systems. Some of the widely used are

1. Spray lubrication
2. Dry Sump Lubrication
3. Wet sump Lubrication
4. Total loss lubrication

A. It should be noted that designing a lubrication system is having a lot of background to it and has to be integrated separately in the engine. This makes 4-stroke engine bulky one. In simple words, it can be summarized as
4 stroke engine=power producing mechanism+Lubricating mechanism.
In two stroke engines no such elaborate arrangement is done.

B. 2 stroke engines are a type of primitive engines and 4 strokes are the advanced version of it (just to remove fuel loss). You see that engine gets more time in cooling in 4 strokes rather than in 2 stroke where power developing process occurs at double speed. hence we would require very advanced mechanism of engine lubrication.

Looking at the size of 2 stroke engine and its power strokes, it makes sense that while it handles fuel, at the same time we should supply oil too.

Well the above is just my observations that I have came against while studying. There is also more to it. Perhaps you should also look at how 4 stroke lubrication works.
If you have any difficulties, do post in this thread!


    Thanks Issue, but i was quite aware of this fact. My ques was that 'why is it not possible to have the mechanism in 2 stroke engine?'. Why can't a 2 stroke engine made to work like a 4 stroke engine(in lubrication)? Another ques: Why doesnt a petrol itself act as a lubricant?
    Why does a 2 stroke engine is preferred in vehicle? If you are desirous of getting power ( Because of its high power producing capacity and its design), efficiency does not matter here much. If you are going to employ lubricating mechanism design parameters might get affected.
    It isn't that no lubricating mechanism is employed. We mix oil with petrol. That much is sufficient.
    If you are going to make other elaborate arrangements, then naturally the cost will increasing and economical considerations will come into picture. In such a case, 4-stroke engine is a viable option.

    You can have lubricating mechanism in 2 stroke anyway if you are determined. Interesting concept though!

    Now why petrol doesn't act like lubricant?
    Good thinking. But Petrol is a fuel. You cannot guarantee that once after absorbing heat from engine, the petrol will not burn outside combustion chamber. It will only jeopardize the security of passengers.
  • Gurjap
    Okay, I see that a lot of people don't like the 2 Stroke engine here 😀

    But think about it: 2 stroke engines are more compact, less bulky and use a brilliant idea (scavenging) to generate power while cutting the generation time in half and being rid of valves and their timing mechanisms. The one reason they were replaced by 4 stroke engine was that they ran hotter (meaning more NOX) and produced a load of unburned hydrocarbons.

    As for why we mix lubes into the gasoline for a 2 stroke, it is obvious once you study the working of a 2 stroke engine. The gas+lube is usually compressed in the crankcase by the rotating crank before being injected into the cylinder. So it makes sense to mix the lube into the gas. While swirling around in the crankcase, the lube can lubricate the piston, the wrist bearing, the crank pin and the power shaft bearing. The lube will still cause burning problems in the piston when it is burned alongside the gas, and the exhaust will be dirty. However, the construction of the engine is much simpler this way; you don't need a separate inlet or storage or pump for the lube.

    Please understand that what I've said holds true for carbureted systems, in modern fuel injectors, the only time the gas comes in contact with the air is when they burn together in the cylinder. This time, you probably won't mix the lube in the gas, and store it separately.
  • Abhilash T Anto
    Abhilash T Anto
    nowadays 2 stroke engines are not available in market since high scavenging and pollution .not only that mileage is also low...
  • Gurjap
    not for automobiles maybe, but Wartsila and other Marine Engine makers do use two-stroke diesel engines for propelling ships.

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