Authors: Sonny Barger
Overhead-cam engines are more efficient and generate more power than pushrod engines, all else being equal, because they keep the valves under more direct control, allowing the engine to rev higher before valve float sets in. Valve float occurs when the cam pushes open the valve more rapidly than the valve spring can close it—it’s a bad thing. If your bike is equipped with a tachometer, it will have a red zone marked on its face beginning at a certain rpm (revolutions per minute) range. The rpm range where the red zone begins is called the “redline,” and is usually the engine speed at which valve float sets in. If you run your tach needle past the redline, you can destroy your engine.
Having an engine explode between your legs is not an experience I’d wish on my worst enemy. It’s rare that a motorcycle engine will explode like a grenade, sending shrapnel outside the engine cases, but what happens when you spin a bearing or throw a rod can be just as deadly.
Usually you’ll be going faster than you should be when this happens, which may well be why your engine explodes. You’ll be riding along, enjoying the open road, and your engine will seize up. This in turn stops your rear tire from turning and it happens in less time than it takes for your heart to beat. If you’re not covering your clutch (we’ll discuss this in the advanced riding section of the book) and don’t immediately pull in the clutch lever to disengage the rear wheel from the seized engine, you’ll skid out of control and crash.
If your bike starts to skid sideways before you pull in the clutch, you’ll have an even worse crash. When your tire is skidding, you lose all traction. When you pull in the clutch and the tire starts turning again, you’ll regain traction. If your bike has started to skid to one side or the other, when you regain traction it will snap back in the opposite direction. This can easily happen with such force that it launches the entire motorcycle in the air. Of course you’ll get launched with it. This is called “high-siding,” and short of hitting a tree or a guardrail, it’s about the worse kind of single-vehicle crash you can have on a motorcycle.
Overhead-cam engines have much higher redlines than do pushrod engines, which is why they produce more power, but that isn’t the main reason I advise against buying most of the bikes that use pushrods. During normal street driving you seldom get anywhere near the engine’s redline; the problem is that most of the engines that use pushrods use other outdated technology, too, which is why pushrod engines tend to be less reliable than those with overhead cams.
ENGINE TYPES
T
HERE ARE AS MANY
different types of four-stroke motorcycle engines as there are types of motorcycles. Several basic engine configurations exist, and unless you plan to drop a fortune buying some rare, exotic machine, the bike you end up with will feature an engine in one of the following configurations:
There are a few oddball designs other than these, but without exception they will either be antiques, or they will be rare (and expensive) exotics, both of which are better suited to collections sitting in museums than they are for useful transportation because the spare parts needed to keep them on the road will be virtually unobtainable.
For example, over the years there have been a handful of motorcycles built with V-8 engines, like the racing bikes Moto Guzzi made in the mid-1950s. Over the years a few other manufacturers have built V-8-powered motorcycles, but not many. Italian Giancarlo Morbidelli developed a V-8 sport bike in the mid-1990s, but at a price tag of $60,000, he only sold four of them. A company called Boss Hoss makes gigantic motorcycles powered by automotive-type V-8 engines, but these bikes are so huge that they are just novelties even for experienced riders. They’re expensive novelties, too, starting at around $40,000 for a base model and climbing well past the $50,000 mark if you start adding accessories; most owners then end up dropping another $20,000 converting them to trikes because they are so huge that they’re miserable to ride.
There have been a few other oddball designs, like the inline six-cylinder bikes built by Honda and Benelli in the 1970s and early 1980s, but these weren’t the most practical motorcycles even when they were new. The odds that you will end up with a bike that uses an engine configuration not on the preceding list are too small to measure.
Single Cylinders
The most basic type of engine, and the earliest to be mounted on a two-wheeled machine, is the single cylinder. As the name implies, this is an engine with a lone cylinder. These engines have always been mounted in a motorcycle frame with the engine aligned with the wheels; the engine has been angled anywhere from a slight lean toward the rear wheel, as on the very earliest Indians from 1901, to a complete forward lean, with the cylinder laying flat, parallel to the ground, its top end pointed at the front wheel, as on a Honda Trail 70 or a Harley Sprint or a Moto Guzzi from the 1960s.
Today most of the single-cylinder bikes available are designed for riding off-road. People who ride off-road place more value on agility and light weight than they do on overall power output. Anyone who’s ever had to pick up a fallen motorcycle on a rough dirt trail will understand the reason for this. Because of the nature of off-road riding, where you’ll find yourself negotiating steep, narrow trails covered with boulders and logs and maybe even the remains of Jimmy Hoffa if you get far enough off the beaten path, off-road motorcycles tend to fall over on a regular basis. This is why the fenders, gas tanks, and many other parts of an off-road bike are made of soft, bendable plastic. The lighter and easier to maneuver a motorcycle is, the less likely you are to fall over in the first place, and the easier the bike will be to pick up when you inevitably do fall over.
There are a few single-cylinder street bikes on the market, too, but most of these are very small displacement machines, usually 250 cc and under. Although these may be adequate for some riders, they won’t cut it for most bikers.
Suzuki has built a 650-cc cruiser-type bike for many, many years. The company used to call it a “Savage,” which is ironic, given the bike’s docile nature—it’s about as savage as an angry Yorkshire terrier. In 2005 Suzuki renamed it the “S40,” which probably stands for “single cylinder, 40 cubic inches.” It’s not a sexy name, but then it’s not the most exciting motorcycle. The single-cylinder engine is on the gutless side, and it’s far from a smooth-running machine—you won’t be doing thousand-mile days on this thing—but it is adequate for a lot of people. You could consider this motorcycle the baseline for what constitutes an adequate motorcycle for full-sized adult people; anything smaller and less powerful will be too small and too underpowered for serious consideration.
V-Twins
The early single-cylinder engines didn’t put out a lot of power; ratings of 3 or 4 horsepower weren’t uncommon. To put that in perspective, the engine in the Suzuki S40, which I just called “gutless,” puts out about 28 horsepower. Even at the beginning of the twentieth century, 3 horsepower was inadequate for most riders—these early bikes needed pedal-assist to produce enough power to climb even the smallest hill—so motorcycle manufacturers looked for ways to increase power output.
The quickest way to get more power is through more engine displacement. This has always been true, and it was especially true in the early years of motorcycling because of the primitive engine technology of the day. Riders needed bigger engines, but the technological limitations of the day prohibited engineers from simply enlarging the early single-cylinder engines. These limitations still exist, to some degree. If engineers make engines with bores that are too large, they run into breathing and combustion problems; if they make the strokes too long, they run into problems with piston speeds.
Given that cylinders could only get so big, the obvious way to get more power was to use more cylinders. The very earliest multi-cylinder engines were V-twins—that is, engines with their cylinders arranged in a V shape. This made a lot of sense at the time since motorcycles were still just motorized bicycles (which is why the pedal-assist system was still in place). A bicycle frame comes to a pronounced “V” at its base, right where the engine sat. Giving the engine a V shape made the engine fit the available space better.
Even though V-twins were the earliest type of multi-cylinder engines, they still have a lot to offer. In street bikes, they generally tend to be low-revving engines that produce large amounts of low-end torque.
Twisting Force
In the real world, torque means more than raw horsepower. Torque is the measurement of the twisting force generated by an engine. Since this twisting force is what twists the wheel around in circles and makes you move down the road, you feel torque a lot more than you feel raw horsepower.
This is where big V-twin engines like those found in Harleys and Victories perform well. A 600-cc sport bike like Yamaha’s R6 produces a lot more power than Harley’s latest 96-cubic-inch (1584-cc) engine: 112 horsepower for the Yamaha compared with 68 horsepower for the Harley.
If ultimate horsepower output was the only factor determining what motorcycle to ride, we’d all be riding Japanese sport bikes, but there’s a lot more to picking out a good, all-around motorcycle than pure engine output. For a lot of people the 68 horsepower generated by a stock 96-inch Harley Twin-Cam is adequate as long as the torque output is sufficient.
The 2006 Yamaha R6 generates just 43 pound-feet of torque, while the 96-inch Harley V-twin cranks out about 77 pound-feet of torque and the V-twin in my Victory Vision produces 109 pound-feet of torque. That doesn’t mean my Victory is faster; the Yamaha is so much faster that they are almost like two completely different vehicles. But to get speed from the Yamaha, you have to rev the engine way up past 10,000 rpm. In other words, to go fast, you pretty much have to ride it like you stole it, all the time. This is fun on a racetrack, if you know what you’re doing, but out among the traffic found on real-world roads, it gets tiresome.
With a big V-twin like my Vision, peak torque is reached at just 2700 rpm. That means when I want to get access to my engine’s twisting force, I don’t have to shift down four gears, open up the throttle, and drive like a maniac. I just roll on the throttle and the power is instantly there. So while a sport bike like the Yamaha is a lot faster on a racetrack, a big V-twin like the Vision feels a lot faster in normal driving conditions on real-world roads.
There aren’t many things in life I enjoy more than the feel of riding a motorcycle with a big, torque-rich engine. When I roll on the throttle, I feel an invisible hand pressing down on me. I feel like I’m part of the road, like I’m connected to the earth by something more than just the rubber of my tires.
L-Twins
Many people might argue that the L-twin engine design is really the same as a V-twin, and they would have a good argument. The L-twin is just a V-twin with the angle between the cylinders opened up to 90 degrees, so that the engine resembles an “L” rather than a “V.”
The reason I broke this design out wasn’t because I think it’s a separate engine design; I did it because the L-twin is generally used in a different type of motorcycle. With a few exceptions, the V-twin engine tends to be used in large motorcycles designed for relaxed types of riding. The Italian companies Aprilia and Moto Guzzi make V-twin sport bikes in very low volume, as does the Austrian company KTM, and Honda and Suzuki have produced a number of V-twin sport bikes over the years, but for the most part V-twin engines power big touring bikes and cruisers.
That doesn’t mean the V-twin engine doesn’t have potential as a high-performance engine. For decades Ducati has built V-twin engines that have been winning world racing championships. But Ducati uses a 90-degree angle in its V-twin engines, with one cylinder laying flat, almost parallel to the ground, and the other almost upright, tilted back only slightly, so many people refer to these as L-twins.
Parallel Twins
Another early type of multi-cylinder engine was the parallel twin. This is an engine with its two pistons arranged side by side. The British company Triumph popularized this engine design. In 1937 Edward Turner developed the Speed Twin for Triumph basically by grafting two Triumph single-cylinder engines together in a side-by-side fashion. He was far from the first to build this type of engine, but Turner’s 500-cc Speed Twin was the first commercially successful mass-produced British multi-cylinder motorcycle, and the basic design has defined the British motorcycle to this day.
When John Bloor resurrected the bankrupt Triumph in the late 1980s, he was determined to build modern, cutting-edge motorcycles rather than retro throwback twin-cylinder machines, but after more than a decade he finally relented, and in the early 2000s the company once again began building traditional parallel-twin motorcycles. Today Triumph’s retro-styled twins are among its most popular machines.
There aren’t a lot of parallel twins on the market today, but those that are available are decent, practical motorcycles. In addition to the Triumphs just mentioned, Kawasaki makes several mid-displacement parallel twins.
Opposed Twins, Fours, and Sixes
Another type of twin-cylinder engine that’s been around almost as long as the motorcycle itself is the opposed twin. This is a two-cylinder engine with pistons that move outward, directly opposite from each other. Since a Harley has a 45-degree V-twin engine, a Ducati a 90-degree V-twin engine (an L-twin), you could almost think of the opposed twin as a V-twin with a 180-degree angle between the V, but if you follow that logic, you could consider a parallel twin a V-twin with a 360-degree angle (or a zero-degree angle, if you don’t want to take the long way around), but this is, of course, nonsense.
Anyway, in an opposed twin, the pistons move outward, away from each other, then inward, toward each other. Early on someone figured this motion resembled the arms of a boxer, but any boxer who boxed with a motion like this would get his ass kicked regularly and severely. Regardless, the name stuck and opposed engines are called “boxers.” Volkswagen used a boxer-type engine in its old air-cooled Beetles, and Porsche and Subaru continue to use boxer engines in their cars.