The Basics
The most recognized difference between 2-stokes and 4-strokes is the engine cycle. The engine cycle simply denotes that when the piston goes up, the spark plug ignites fuel, and therefore creates a power stroke. Two-strokes fire every revolution. Four-strokes fire every other revolution.
Lubrication
Two-strokes lubricate their moving parts with 2-stroke oil either mixed in with the gas, injected in the combustion chamber, or in the intake track. Four-strokes lubricate their moving parts with motor oil that is pumped through the engine.
A Visual Guide
There are a few basic ways that you can visually tell the difference between a 2-stroke and a 4-stroke. Two-strokes usually have an expansion chamber on the pipes (where they are very large in diameter at one point and then taper back down to smaller at another point)- a feature that is more noticeable on some models than others. Four-strokes, on the other hand, typically maintain the same diameter throughout the pipe until the muffler.
Another way to visually spot the difference between the two is the detection (or lack thereof) of smoke when the machine is running. Two-strokes smoke when running (as they should- if it isn’t smoking there’s a problem), whereas 4-strokes do not.
Why do 2-strokes smoke, you ask? Good question! The 2-stroke smokes because it’s burning an oil/fuel mixture rather than just fuel alone. Among 2-stroke riders, there’s an affectionate love of the smell that’s created by the oil in the fuel. There’s even companies who’ve produces candles in the scent (link).
Remember: 2-Stroke Smoke= GOOD; 4-Stroke Smoke = BAD
Audio Indicators
Even if you can’t physically see the machine, a well-trained ear can decipher if a machine is a 2-stroke or a 4-stroke based on sound alone. Two-strokes have a distinct high-pitch, whining sound (or a “ping”), where as 4-strokes have a deeper, lower-pitched sound.
Physical Components
There are also physical differences between the two types. Two-strokes have holes in the cylinders to let air in and out of the combustion chamber, whereas 4-strokes use valves with cams and either a chain, belt, or push-rod setup to let air in and out of the cylinders.
Thus, there are a significant number more moving parts on a 4-stroke than a 2-stroke. In addition, you have to set cam and ignition timing on a 4-stroke. Two-strokes only require ignition timing to be set.
Two-strokes are typically lighter in weight due to less parts, and typically make more power than their same CC 4-stroke counterpart- despite the 2-stroke engines being, on average, physically smaller.
Final Thoughts
We hope this helps clarify some of the very basic differences between two and four stroke cycles. While some of you may find this information redundant or obvious- an explanatory article breaking down these basic differences has been one of our most requested article topics to-date. As always, if you have any additional questions, feel free to reach out. We’re always here to help!
