2-Stroke vs 4-Stroke Engines: What's the Difference?

Two-cycle oil is used in many small engines, from boat motors to chainsaws.

They're often used in small power tools and light vehicles because of their excellent power-to-weight ratio.

Gasoline ignition is especially common in the smallest two-stroke engines.

Their inefficient oiling methods mean less effective lubrication shorter engine life.

Less ash makes burning the oil a bit cleaner.

To maintain their working life, staying on top of lubrication is especially important in two-stroke engines.

The lower number of parts in a two-stroke engine is the primary reason they tend to be lighter.

It only fires once per revolution. This trait helps two-stroke engines produce more power, by weight, than four-stroke engines.

It gets its blue tint from the oil that's blended into the fuel.

At smaller sizes, two-stroke engines aren't really fuel efficient.

These engines can leave clouds of smoke and trails of oil in the water.

The point of the direct fuel injection is to reduce the amount of unburned fuel in the emissions, making them run cleaner.

The upward stroke is the compression stroke, and the downward stroke is called the power stroke.

The range of RPMs that offer peak power on these bikes, known as the power band, occurs in a very limited range.

It combined compression with ignition during each revolution. Clerk succeeded where other inventors had already failed.

Petroil, or two-stroke oil mixed with gasoline, makes the total-loss oiling system work.

The typical compression ratio is 12-to-1. Higher compression ratios generally mean more power.

They are both open. Air pressure differences cause a fresh fuel/air mix to move into the combustion chamber.

It seems bigger really is better when it comes to the efficiency of two-stroke engines.

The crankshaft, which converts the pistons' up-and-down motions into rotation, makes one complete turn each power cycle.

Dugald Clerk invented it in Scotland and patented his creation in England in 1881.

Asymmetrical engine timing often results in better power output.

Scott, who also had about 50 other patents to his name, founded the Scott Motorcycle Company in 1908.

Two up-and-down motions make up the stroke (and the power cycle).

You need 4 ounces of oil per gallon of gas — and it can be pricey, too.

The oil originates in the carburetor and, from there, is mixed directly into the fuel.

In this configuration, the piston covers and uncovers the ports as it travels up and down the cylinder. The 1970s saw significant improvements in piston-controlled inlet ports.

The 6-1 compression ratio, which means the volume of the mixture is compressed by the piston in the cylinder to one-sixth of its original, is fairly low for small engines.

The oil-fuel mixing process is mainly for smaller and cheaper two-stroke engines.

The emissions are higher in large part due to the oil that's mixed with the gasoline.