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2-stroke engines are mostly a thing of the past, but many motorcycle enthusiasts would still love to own one.

In one form or another, the 2-stroke engine has been around for over a century now, and just when everyone thought it was dead and buried as a motorcycle engine, it made its big breakthrough.

At their core, 2-strokes are simple engines that work great for small applications like chainsaws and brush cutters where the tool needs to operate in different orientations. Motorcycles don’t necessarily need that feature, which is why when 4-stroke technology closed the gap on 2-stroke, the 2-stroke bikes all but disappeared.

Their main drawback is emissions, but they do have a lot going for them and now have a trick up their oil-burning sleeve that is able to combat all those unburned hydrocarbons.

There was a bit of a myth that they were low maintenance, and although it is true in some respects, most high performance 2-stroke bikes need major overhauls more often than any 4-stroke with the same horsepower.

What they have on their side though is that they are much easier to take apart, and give novice mechanics more room for error.

What makes them easier to maintain is the fact that they are relatively straightforward in principle, only needing the three main elements for combustion; air, fuel and spark.

Fuel and oil are integrated, so there are no oil changes, and you get a power stroke every two cycles instead of 4, so they can rev much higher, much faster and harder.

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With the oil and fuel mixed, there is no need for an oil pump/lubrication system, and there is no need for valves.

It has a reed valve that lets air in, then the spark plug simply ignites the fuel mixture, burnt gasses will flow out of the exhaust port into an expansion chamber. It is a fairly thermal efficient process too, so most 2-stroke designs don't need water cooling either.

The thing that really makes them stand out is the way they make their power, some will hate it, and others will love it, but it is their defining feature.

Almost all their power lies high up in the rev range, much like old turbos had a lag before they put their power down, a 2-stroke will do much the same. When it does come “on the pipe” it is exhilarating, as they make far more power per cubic inch than 4-strokes, and a sound everyone will immediately recognize.

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The fact that it has fewer parts means that their construction is naturally lighter, but they deliver substantially more power.

As a real world example, the Yamaha YZ250 (2-stroke) makes 49 horsepower and YZ450F (4-stroke, pictured) makes 48, the YZ is a particularly glaring example of the gulf in performance because the 250 engine was engineered in 1999 (with some minor revisions along the way) and the 4-stroke 450 got updated in 2018.

So this is something of a moot point on new bikes with electric push-button starters, but once upon a time, this made a very real difference on track.

Kick-starting a 2-stroke is one light kick, the backpressure generated by large single cylinder 4-strokes is enough to kick your leg off the kick-starter and can even cause injury.

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When it comes to putting the oil in the fuel, there is one huge advantage and one rather obvious disadvantage.

With this design, there is no need for a sump or lubrication system that necessitates oil journals that are expensive to design and manufacture. Unfortunately, when it comes to combustion all the efficiency is lost, as the combustion can never be complete and much fuel is wasted, generating more pollution than a similarly powerful 4-stroke.

A valvetrain is expensive to develop, manufacture and maintain. It is also an added failure point for the engine, all 2-strokes just use a simple reed-valve (above) that regulates the air/fuel mixture.

Doing away with the valvetrain makes the bike a lot lighter, less prone to catastrophic failure, and more affordable to both manufacture and maintain.

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Although this might not seem particularly relevant to the motorcycle world, and more useful to other small applications, you will only realize how relevant it is once you fall off your bike for the first time.

On a 2-stroke, the worst thing that will happen is you leak a bit of fuel (they do that anyway) but on a 4-stroke oil can flow into the combustion chamber, making it difficult to start at best and at worst, fouling your plugs and ending your race early.

Arguably the biggest breakthrough for 2-strokes is TPI (transfer port injection) which is currently proprietary technology from the KTM group, but will surely force an answer from Japan at some point.

Effectively bringing fuel injection to the world of 2-stroke bikes is a big deal, firstly it makes the combustion process more efficient, which makes the power delivery better, and secondly, it brings the emissions down to a level that is on par with the 4-stroke competition.

Luke Zietsman is an all out automotive enthusiast based in The Philippines. If it has two or four wheels he has either owned it, researched about it or dreamed about it.