As we have seen in a previous article, a two-stroke engine works mighty differently than a four-stroke engine, although there is still a piston or several pistons that move up and down in a cylinder.

Why is the two-stroke engine's lubrication system different from a four-stroke's?

This working method thus requires a lubrication system that is also different from a four-stroke engine's. This is because the two-stroke engine's crankcase is used to circulate the air/fuel mixture (also called "charge"). As such, there cannot be heavy lubricating oil present in the crankcase.

READ HERE: How does a Two-stroke Engine Work?

Also, the shape of the cylinder has several cutouts along its surface, unlike the four-stroke's which is a continuous surface. A four-stroke has valves in the head, above the piston to allow for gas movement. A two-stroke, on the other hand, had no valves on top and use the cutouts as ports.

This is why lubricating oil cannot be circulated around a two-stroke engine the way is it in a four-stroke engine.

So how does it work then?

The only way is to premix the charge with lubricating oil, which is also known as 2T oil.

The old method of doing so is by mixing 2T directly into the petrol tank. There is a ratio for the mix. However, there are some who say the best is 40 parts fuel to 1 part of 2T (40 liters of petrol:1 liter of 2T = 40:1) while there are those who say 50:1. In any case, mixing these two means the premix needs to go through the carburetor or injector.

Then Yamaha invented the Yamalube system (this was waaay before Yamalube engine oil) which meters the amount of 2T to fuel depending on throttle opening.

In any case, too much 2T will foul the spark plug(s), while too little will cause the engine to seize (jam).

Okay, so back to the question, the two-stroke's lubricating oil is circulated around the engine along with the fuel/air mixture. The concept is blatantly simple. Unfortunately, as we mentioned in the previous article, some of this mixture is leaked into the environment thus why two-strokes are banned.