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Two Stroke Motorbikes Resist Modern Times

It almost seems quite amazing, but given modern pollution laws as well as the advancement of fine quality four stroke motorbike engines that the old two stroke engine design still endures today. Yet, the modern two stroke engine remains as a powerful workhorse for many smaller displacement motorbikes, turning out fine power and torque for the size of engine. And since two stroke engines fire once per engine revolution, there is always the potential of a power output twice that of a similarly sized four stroke design.

My little 2008 Benelli is a pretty good example of a modern two stroke motorbike. For the small 50cc engine size, the bike can nearly top 50mph. And it has great pickup. There is an automatic oil feed system that avoids having to mix oil and fuel. Yet for good reason the two stroke engine designs remain a subject of great controversy. My CPI motorbike is also a two stroke as well. However. I've owned a four stroke before as well. benelli_x50_yellow.jpg

One of the biggest problems associated with the two stroke engine is the higher pollution levels they create. Two stroke engines must use oil in the gas in order to survive, and all produce at least some oil smoke. Especially in Europe, the two stroke designs have become a threatened species as air pollution rules tighten up. Yet fans of two stroke bikes of all types, both motorcycles and scooters, seem to have at least some new two stroke models survive. Even in the U.S., the EPA continues to allow more efficient two stroke motobikes to be sold, however in the future that could all change. However, at some point in the future, new two stroke engines motorbikes are very likely to become an endangered species, much to to the sadness of many motorbike fans.

Before 2006, motobikes with an engine displacement of 50cc or less were exempt from EPA certification. However, since 2006, all motorbike engines that are two stroke must be tested and certified by the EPA. This has made it more difficult for many two stroke models to be imported into the U.S., and probably explains why the 50cc CPI GTR, which has a sport bike type design body and a two stroke engine is no longer imported here. But the four stroke 180cc version is still available. The CPI GTRs are a real popular cult item throughout Europe and Asia, and on Youtube, many videos exist of fans showing off their bikes.

Yet, part of the appeal of the two stroke engine is the unique sound they create, the extra power as well as the smell of the engine. Two stroke engines have an appeal to a motorhead cult of motorbike followers. At one time some automobiles such as Saab actually used some two stroke engines in their modern automobiles as well.

The two stroke is also a simple design to create. There are no valves. However, generally speaking, two stroke engines do not live as long as four stroke engines by any means. However, some pretty good synthetic engine oil on the market will extend the life of a two stroke considerably. However, the four stroke design has many advantages such as better fuel economy and a quieter sound. But since the four stroke only creates power on every other revolution due to the design where intake and exhaust valves must open and close, it may take an engine twice the size of a two stroke one to produce the same level of power. In some 50cc motorbike racing for example, some two strokes can exceed 130km(80mph)an hour, which is an unheard of speed for a similar sized four stroke engine.

And two stroke engines remain a popular design in some yard equipment as well as chainsaws because of the greater power they produce as well. However, as the EPA and other environmental watchdogs become more mindful of the state of the environment as well as growing concerns over global warming my best guess is that the future days of the two stroke might well be numbered. Little doubt in my view that these old style engines with such a simple design , that may not be very fuel or pollution efficient will someday be banned from production by law.

Two stroke engine fans need to enjoy these fun bikes while they're still here.


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Comments (2)


I agree, after the tree hugger's get done with their BS, a lot of things will be gone. By the way, do you remember the Wankle engine. I believe that was a 3 stroke, used in autos that gave very excellent MPG. Somehow that engine was banned in the US. Not because of emissions, but because of the MPG you received.

Hi Allen. We owned one of those rotary engine Mazdas, and we returned it to the dealership within two weeks of owning it because it burnt so much oil and used so much gas. It was a beautiful blue station wagon that I just loved, but the fuel mileage was as bad as a big V8, but it had great power. I joked about it having 6 cylinder power with V8 economy. I do miss that car though.

Those rotary engines used a triangle shaped rotor(probably inspired by a Vick's cough drop) that spins around and creates the power. But like the two stroke design, it appeared to be able to produce great power, but at the expense of burning much fuel and oil. But I think for racing applications, that the design might have held some promise. This engine was the same as the one in their RX7 sports cars.

Chrysler experimented with some cars in 1963 that had a consumer version of a jet engine called gas turbines. The motor spun at around 50,000rpm, and had to be geared down with the transmission to street legal speeds. These also had excessive fuel consumption as well as pollution problems and these engines produced a great deal of heat. But they had tons of power. These gas turbine cars had a ball shaped engine and huge flat dual exhausts. They were far different in design than any auto engine of the time.

Ford had plans to build a small VW sized car in the 1960's that they dropped called the Ford Cardinal. Some plans called for a V4 engine. However, an experimental preMustang model was produced by Ford with a rear mounted V4 engine, and could be seen as a show car at auto shows. The AMC Pacer was supposed to have a new type design GM engine in it, but GM decided not to build these new engines after all, leaving AMC with the serious problem of stuffing their long six cylinder engine in these cars with a short hood. These six's were so long, that the last spark plug was usually never changed in them because you would have to pull the engine out to change it. Finally in the last years, a V8 was put in them, which worked out better because of the shorter overall length. However the fuel mileage wasn't good. And modern pollution controls reduced the V8 power to lackluster levels, but with so much bilk and glass, the heavy Pacers needed a lot of power to move decently in traffic. The Pacer was a pretty good example of a poor late 70's early 80's American car and certainly not even as good as the Gremlin or Hornet by any means, except for options and interior comfort.

The small 1948 Tucker brand of cars had a helicopter engine, which was rear mounted and powerful. But this company had little money to get off the ground, and a magazine article suggested there was some financial fraud involved when Preston Tucker set up some car dealerships and only provided some customers with a set of luggage to go in the front trunk when they made a prepayment to own one of these cars. In the end, I think only about 50 of these cars were actually produced because of all the legal and financial problems from this underfunded company.

But I still remain a fan of the two stroke motorbikes. However if I have to live with a four stroke model in the future, then I understand. But fortunately, not many vehicles on the road use two stroke engines. So this has allowed two stroke engine fans a few years of leeway to enjoy their hobby.


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