Sports Cycle

The Four Stroke : Single Cylinder Engine !

Anyone who has ever added oil to a car has experience with four-stroke engines; the vast majority of roadgoing vehicles ever to turn a wheel on U.S. streets have four-stroke engines.

The four stroke gets its name from the number of strokes the piston makes during each power cycle (each series of events that produces power). The piston first moves down, drawing in the fuel charge (intake stroke), then moves up (compression stroke), at which time the fuel-and-air charge ignites and burns, pushing the piston down (power stroke). The fourth stroke occurs when the piston moves back up, forcing out the burned gasses (exhaust stroke).

The four-stroke engine is sometimes called the Otto cycle, in honor of its inventor, Nikolaus August Otto. It’s called a “four stroke” because the piston makes four strokes, or movements along the length of the cylinder, per cycle.

The Single Cylinder Engine

The single, the most basic of engines, once powered most motorcycles on the road. In the old days, motorcycles were such problematic beasts, the general philosophy held that the fewer moving parts you had, the less the chance those parts would break. And what could have fewer moving parts than a motorcycle with but one cylinder?

As designs and materials advanced, along with production techniques, manufacturers were able to create ever more complex motorcycles, with two, three, four, six, and even eight cylinders. Generally speaking, the more cylinders you have, the smoother the engine runs. Clever designers have produced twin-cylinder engines that run almost as smoothly as four-cylinder engines, but there is no way to make a single cylinder do so, and as a result, single-cylinder streetbikes have steadily lost popularity since the very beginning of the sport.

Today’s big singles use counterbalancers (weights inside the engine) to cancel out some of the vibration to a certain degree, but you can’t take the thump completely out of a thumper (a bike with a large-displacement, single-cylinder, four-stroke engine, so called because of the thumping sound of its exhaust).

Another drawback of single-cylinder engines is that they don’t make a lot of power. But singles have advantages, too. Because they have few parts, they tend to be light power plants (engines), which is why they are so popular in the big dual sports. And while they may not generate a lot of power, they still provide satisfying amounts of torque.

Suppose that you are riding a BMW F650ST single. Beside you, your companion rides a Suzuki GSX-R 600, a four-cylinder bike that makes more than twice as much horsepower as your Beemer, but roughly the same torque. You pass the city limits, and the speed limit rises to 65. Say, for the sake of argument, that you’re both running at roughly 2500 RPMs. You both whack open the throttle at the same time. You’ll pull away first-even though the Suzuki has twice as much horsepower - because at 2500 RPMs, you have about 34 foot pounds of torque available to you, while the Suzuki only has about 22 foot pounds of torque available (torque, the force the engine exerts on the rear wheel, is measured in foot pounds).

Of course, within a few seconds, the Suzuki will have rocketed away from you when all that horsepower kicks in, but by then you are both going faster than the powers that be will allow anyway. And should the Suzuki rider drop the shifter down a few gears, she will have left you behind from the moment you hit the throttle. Either way, she will have accelerated to go-to-jail speeds quicker than you can process the sound of the sirens on Officer Bob’s police cruiser as he begins high-speed pursuit.

The point of this hypothetical scenario is that while single-cylinder bikes offer less overall power than multicylinder bikes, the power they do offer is often more usable in the real world, a world populated by traffic lights, stray dogs, pedestrians, senior citizens, and lawenforcement officials. The same is true of many twincylinder motorcycles.