Sports Cycle

Are you often confused by some of the things your bikers friends say ? Like any hobby or geek-o-meter, there are common motorcycle terms that we all come to learn, and then there is some of the more bizarre slang you can spend a lifetime behind the engine never understanding. Below we’ve compiled a collection of common Motorcycle and Bikers slang to help lift the veil on their mystery.

A

ABS (Antilock Brake System) : The ABS detects when a wheel is not turning and releases pressure to the brake on that wheel, preventing a skid.

Aftermarket : The sector of the market that sells parts and accessories other than OEM (Original Equipment Manufacturers).

Airheads : A term for older, air-cooled BMW Boxer Twins.

Ape hangers : A term coined at the height of the custom-bike movement to describe tall handlebars that forced the rider to reach skyward to grasp the controls, making the rider adopt an ape-like posture.

B

Bagger : A motorcycle equipped with saddlebags and other touring amenities.

Belt-drive system : A final-drive system that transmits the power to the rear wheel via a drive belt.

Big Twins : The engines in the larger Harley-Davidson bikes.

Bobbers : The custom bikes American riders built after World War II where the owners cut off, or “bobbed,” much of the bodywork.

Bottom end : The bottom part of the engine, where the crankshaft and (usually) the transmission reside.

Boxer : A two-cylinder engine with the pistons opposing each other, resembling fists flying away from each other.

Brakes (disc and drum) : Disc brakes are located on the front tire and use stationary calipers that squeeze pads against the discs that rotate with the wheel. Drum brakes, on the other hand, are located on the rear wheel and use horseshoe-shaped brake shoes that expand against the inner surface of the wheel hub.

C

Café chop : Converting a stock motorcycle into a café racer is known as doing a café chop on a bike.

Café racer : Motorcycles modified to resemble racing motorcycles from the 1950s and 60s. They are called “café racers” because their owners supposedly raced from café to café in London, where the bikes first appeared in the 1960s.

Cam (camshaft) : A rod with lobes on it that opens the valves.

Carbon fiber : A high-tech material favored in many motorcycle applications because it is extremely strong, light, and inexpensive. The distinctive look of carbon fiber has become trendy.

Carburetor : A device that mixes fuel with air to create the fuel charge burned in the combustion chamber.

Cases : The two clam-shell-like halves in the bottom end of the engine surrounded by a metal shell.

Centerstand : A stand that supports the motorcycle in an upright position.

Centerstand Tang : A small lever attached to the centerstand.

Chain drive system : A final-drive system that transmits the power to the rear wheel via a chain.

Chassis : The combined frame and suspension on a motorcycle.

Chopper : Once used to describe a custom motorcycle that had all superfluous parts “chopped” off in order to make the bike faster, a chopper today is a type of custom bike that usually has an extended fork, no rear suspension, and high handlebars.

Clip-ons : Handlebars that attach directly to the fork tubes, rather than to the top yoke, that hold the fork tubes together.

Clutch : A device that disengages power from the crankshaft to the transmission, allowing a rider to change gears.

Combustion chamber : The area at the top of the cylinder where the fuel charge burns and pushes the pistons down.

Coming on the cam : The term used when a four stroke reaches its powerband.

Coming on the pipe : The term used when a two stroke reaches its power band.

Connecting rods : These attach the crankshaft to the pistons via the eccentric journals, and the rods’ up-and-down movement is converted into a circular motion through the design of the journals.

Constant-radius turn : A turn with a steady, nonchanging arc. In a decreasing-radius corner, the arc gets sharper as you progress through the curve, while in an increasing radius corner, the arc becomes less sharp.

Contact patch : The area of your tire that actually contacts the road while you ride.

Counterbalancer : A weight inside an engine that cancels out some of the engine’s vibration.

Countersteering : The way you use the handlebar to lean the bike into a turn. If you want to turn right, you push the handlebars to the left, and vice versa.

Cowlings : A piece of bodywork that covers the engine area.

Crotch rocket : A term some people use to refer to sportbikes.

Crowns : The tops of the pistons.

Cycle : The up-and down motion of the piston. The terms cycle and stroke are used interchangeably when referring to engine types.

Cylinder block : The hunk of aluminum with holes bored through it, inside which the pistons move up and down.

Cylinders : The hollow shafts in the top end of an engine inside which internal combustion occurs.

D

Decreasing-radius corner : A turn where the arc gets sharper as you progress through the curve.

Dirtbike : Bikes intended for off-road use that aren’t legal to ride on public roads. Sometimes the term pure-dirt is used to distinguish a dirtbike from a dual-sport motorcycle.

Discs : These are the metal rotors the caliper presses the pads against to brake.

Double-cradle frame : A bike frame with two steel tubes circling the engine from the front and “cradling” it.

Dresser : A motorcycle set up for long-distance touring.

Dual sport : Street-legal motorcycles with varying degrees of off-road capabilities. Also called dual-purpose motorcycles.

Eccentric journals : These are used to attach the connecting rods to the crankshaft (also called metal shafts).

Ergonomics : The science used to design devices, systems, and physical conditions that conform to the human body. A prime consideration when designing a motorcycle.

Evolution (Evo) : When Harley-Davidson began using aluminum to build its cylinder jugs, it called this new engine the Evolution.

F

Fairings : The devices mounted at the front of a motorcycle to protect the rider from the elements. These range from simple, Plexiglas shields to complex, encompassing body panels.

False neutral : When you fail to engage gears and the transmission behaves as though it is in neutral, even though it isn’t.

Flat cylinders : Found in the flat-four- and flat-six-cylinder engines used in Honda’s Gold Wings, the cylinders are arranged in a flat, opposing configuration.

Foot paddling : The way an unskilled rider “walks” his or her motorcycle around at low speeds.

Forks : The metal tubes holding the front wheel to the rest of the motorcycle.

Four-cylinder bike : A motorcycle with four cylinders.

Fuel-injection system : This mixes the fuel-air charges and forcibly injects them into the combustion chambers, unlike carburetors, which rely on the vacuum created by the engine to draw the charges into the combustion chambers.

G

Garbage wagon : A scornful term used by some outlaw bikers to describe touring bikes.

Gearhead : A person with a strong interest in all things mechanical; a motorcyclist.

Gearset : A set of gears within a bike’s transmission.

H

High siding : Pitching a bike over away from the direction you are turning. The most dangerous kind of crash.

Horsepower : A measure of an engine’s strength.

Hydroplane : When your tires start to float on top of water, causing them to lose contact with the road’s surface.

I

Increasing-radius corner : A turn where the arc becomes less sharp as you go through the curve.

Inline six : An engine with six cylinders in a row.

Inline triple : An engine with three cylinders placed in a row.

Iron Butt Rally : The most grueling long-distance motorcycle rally in the world. To finish, the rally requires that you ride at least 10,000 miles in 11 days.

K

Knucklehead : A term for Harley-Davidson’s first overhead-valve Big Twin, introduced
in 1936.

L

L-twin engine : A V-twin engine with its cylinders splayed apart at a 90-degree angle, which creates a smoother-running engine. These engines can either be placed transversely (crosswise), or longitudinally (lengthwise) in the motorcycle frame.

Lane splitting : Riding between lanes of traffic on a freeway.

Laying the bike down : A crash where you slide down on one side of the bike.

Leviathan : Used to describe big, multicylinder dual sports.

Lugging the engine : Letting the RPMs fall below the engine’s powerband.

M

Manual transmission : A device consisting of a set of gears (the gearset), that alter the final-drive ratio of a vehicle to enable an operator to get up to speed. Automatic transmissions do not have gearsets but rather use a complex system of fluid and metal bands to vary the final-drive ratio of a vehicle.

N

Naked bikes : Bikes without any type of fairing.

O

Oilheads : Newer, air-and-oil-cooled BMW Boxer engines.

Open-class : When referring to street-legal sportbikes, open-class designates motorcycles with engines that displace more than 800 cubic centimeters of volume.

Original Equipment Manufacturers (OEM) : The companies that build the bikes.

Orphan bikes : Rare bikes that are no longer in production.

Otto cycle : The four-stroke engine is sometimes called the Otto cycle, in honor of its inventor, Otto Benz.

Overbore :When you overbore your engine, you drill out the cylinders and then put oversized pistons in the holes, effectively increasing your engine capacity.

Overhead cam system : A system where the cam rides directly on top of the valve
stems.

P

Panhead : A term for Harley-Davidson’s second-generation overhead-valve Big Twin, introduced in 1948.

Parallel-twin engine : A two-cylinder engine with its cylinders placed side-by-side in an upright position.

Pistons : The slugs moving up and down within the cylinders.

Powerband : A certain RPM (revolutions per minute—how many times per minute an engine’s crankshaft spins around) range in which an engine makes most of its power.

Primary drive : A drive chain connecting the engine’s crankshaft to its transmission.

Production motorcycles : The bikes manufacturers produce to sell to the general public, rather than bikes built specifically for racers.

Pushrod system : In a pushrod system, the cams are located below the cylinder heads and push on the rocker arms by moving long rods, called the pushrods.

R

Radial : When used to describe a tire, refers to the way the cords of a tire are constructed. While radial tires have long been used with automobiles, they are just now being used on motorcycles.

Rain grooves : Channels cut into a road’s surface to help water run off the road during a rainstorm.

Repair link : A link in some motorcycle chains that can be disassembled for chain repair.

Repli-racers : Hard-edged sportbikes. These motorcycles are characterized by riding positions that tuck the rider into an extreme crouch, forcing him or her to practically lay down on the fuel tank.

Revolutions per minute (RPM) : The number of times the crankshaft spins around each minute. Often, the term revs is used, especially in conversation.

Riding two up : Carrying a passenger on your bike.

Rocker arms : Devices that work like upside-down teeter totters and push on the valve stems.

Rubber-mounted : Rubber-mounted engines use a system of rubber cushions and/or jointed engine mounts to isolate engine vibration from the rider.

S

Shaft drive system : A final-drive system that transmits the power to the rear wheel
via a drive shaft.

Shaft jacking : Shaky or bumpy motion created by the impact of acceleration and then fed back into the bike’s frame.

Shovelhead : A term for Harley’s third-generation overhead-valve Big Twin engine,
introduced in 1966.

Sidecars : Small carriages attached to the side of a motorcycle to provide extra carrying
capacity.

Sissy bar : The backrest put behind the passenger’s portion of the saddle.

Snicking : The act of shifting a well-functioning transmission is often called snicking, because that’s the sound the action makes. A transmission that doesn’t snick into gear is described as sloppy-shifting.

Solid-mounted : A bike with a solid-mounted engine has the engine bolted directly to the frame tubes.

Splitting the cases : The metal shell surrounding the bottom end is composed of two clam-shell-like halves, called cases. Taking these apart to repair the motor is called splitting the cases. See also bottom end.

Sport tourer : A motorcycle that combines the comfort and carrying capacity of a touring bike with the handling and power of a sportbike with larger fairings and hard, lockable luggage.

Sportbike : A motorcycle designed for optimal speed and handling characteristics, often with extensive bodywork.

Springer fork : Springer-type forks use large, exposed springs to dampen the impact of road irregularities.

Squid : Someone who rides a sportbike on the street as if he or she were on a racetrack.

Steering geometry : The geometrical relationship between the motorcycle frame, the angle of the fork, and the position of the front tire.

Streetfighter : A bare-bones sportbike, stripped of all extraneous body work (also called a “hooligan” bike).

Stroke : The up-and-down motion of the piston.

Suspension : The forks, shocks, and to a degree, tires, of a motorcycle. The springs and fluids in these items that “suspend” the motorcycle frame off of the ground.

T

Tappets : Small metal slugs between the cam and the pushrod or rocker arm.

Telelever system : The most successful alternate front suspension, made by BMW, which takes the shock-absorption function of a hydraulic fork and transfers it to a shock absorber located behind the steering head.

Thumper : Bikes with large-displacement, single-cylinder, four-stroke engines.

Top end : The upper part of the engine, which contains the pistons, cylinders, and valve gear, and the induction system consists of the apparati that mix an air-and-fuel charge and inject it into the combustion chamber, located in the top end.

Torque : A twisting force, and in a motorcycle, it is a measure of the leverage the engine exerts on the rear wheel.

Touring bike : A bike equipped for longer rides with fairings and lockable saddle bags.

Traction : A tire’s ability to grip the road.

Travel : The distance that suspension components, the forks and shocks, move up and down when the bike rides over bumps.

Twin spar-type frame : A bike frame with two steel or aluminum “spars” (flat beams) sandwiched around the sides of the engine.

Two up : A term for carrying a passenger on your motorcycle.

Two-stroke engine : An engine (also called a “stroker”) whose power cycle consists of just two movements, or strokes: The piston moves down, drawing in the fuel-air charge, and then up, combusting the charge.

U

Unitized transmission : A transmission (often referred to as a “unit transmission”) that is an integral part of the engine’s bottom end.

Universal Japanese Motorcycle (UJM) : During the 1970s, the Japanese became so identified with the four-cylinder, standard-style motorcycle that this term was coined to describe them.

V

V-four : An engine with four cylinders arranged in a V-shaped configuration.

V-twin : A two-cylinder engine with its cylinders placed in a V shape.

Valves : Devices consisting of metal stems with flat disks on one end that open and
close to let fuel charges in and exhaust gases out.

Valve guides : Metal tubes that house the valves.

Valve train : The system of valves that let the fuel charges in and let the exhaust
gases out.

You now have a fair idea about what all that commotion taking place down below your legs is all about, but really, it means nothing if you have no way of transmitting that commotion to the back wheel of your bike.

As with many other aspects of motorcycle technology, the three final-drive systems most commonly used today - chain, shaft, and belt - had all been tried before the European squabbling that started World War I got out of hand.

In Chains

In the early years of the sport, the crude belt system mentioned earlier was employed, but by the end of World War I, most manufacturers had settled on a chain-drive system (although a few opted for drive shafts). The simplicity and ease of repair of a chain-driven system made it a logical choice back then.

In this system, a sprocket mounted to an output shaft in the transmission is connected to a sprocket attached to the rear wheel of the motorcycle by the drive chain. Although such a setup requires periodic maintenance (the rear wheel needs to be adjusted to take up the slack created in the chain as it stretches over time), the benefits of this system make it popular to this day.

Unlike shafts, chains absorb much of the impact created during acceleration (which is the main reason they stretch over time). Shafts, which are much more rigid than chains, feed that energy back into the frame, causing all kinds of funky motion that a rider feels. This motion is called shaft jacking, and while it’s not a serious problem in most real-world riding conditions, it detracts from a bike’s handling.

Probably the biggest drawback of chain drives is that they are messy. In addition to needing to be tightened, they need to be cleaned and lubricated on a regular basis. The solutions used to do this are sticky and greasy, and they tend to fly off chains and onto a rider’s jacket and clothes.

Getting the Shaft

Shaft-drive final-drive systems transmit the power to the rear wheel via a drive shaft. The chassis refers to the combined frame and suspension on a motorcycle.

Shaft drives do affect handling: They transmit the energy a chain absorbs directly to the chassis (the combined frame and suspension), causing the rear of the motorcycle to move up when it should move down and vice versa. Still, shaft drives are popular because they are so convenient and low-maintenance, especially when traveling. It’s hard enough packing a motorcycle for an extended trip without having to put cans of lube and cleaning solvent in your duffel bag next to your shirts and underwear. Because of this, the most popular touring and sport-touring bikes have shaft drives.

A couple of clever companies (BMW and Moto Guzzi) have all but eliminated the antics associated with shaft systems by using creative rear-suspension geometry. By arranging suspension components in a parallelogram-type position, the rear suspensions on these bikes feed the shaft-jacking motion into the frame along a horizontal axis rather than a vertical axis, converting the up-and-down motion into a forwardand - backward motion. The rider hardly notices this sort of movement.

While the shaft’s acrobatics can be overcome by clever designers, another drawback of shaft systems cannot be overcome so easily: their weight. Shaft drives are heavy, and that weight is unsprung, meaning that it is not supported by the suspension. Unsprung weight tends to decrease the bike’s capability to switch directions more than the same amount of weight carried by the suspension. Because it is more directly connected to the road than weight supported by the suspension, unsprung weight has a disproportionate (and negative) effect on handling.

The drawbacks of both shaft and chain systems led some companies to explore an old alternative: belt drives.

Belt It Out

Although belt drives were abandoned early on, by the beginning of the 1980s, advances in materials had once again made them a viable alternative. Harley-Davidson was the first to reintroduce the concept, equipping special-edition bikes (like its original Sturgis model) with both primary and final drive belts. The primary belt system never caught on, but the final drive belt did, and today every Harley made comes standard with such a belt. Kawasaki also experimented with belts on some of its small displacement bikes.

The advantages of belts over chains are that belts are much cleaner, requiring neither messy lube nor cleaning solvents. While they do need periodic adjustments, they need such attention less frequently than chains. The advantages of a belt system over a shaft is that belts, like chains, do not transmit unwanted motion into the chassis. They also do not come with the unsprung-weight penalty of a shaft system.

The disadvantages of belt systems, at least in the case of Harley-Davidson’s application, is that they are true buggers to replace when they do go bad, especially on the big twins. Except for certain models, most big twins require that you partially disassemble the frame in order to replace a belt. And to replace a belt on all big twins, you must remove the primary drive and clutch assembly, which is no small job.

This disadvantage has been negated on many of the newer bikes using belts. Victory uses a removable subframe spa to ease belt replacement, as does the Buell Firebolt. Such convenient features makes belt drive increasingly attractive. Even BMW uses a belt on its latest rendition of its F650GS Single.

One of the major obstacles designers of early motorcycles faced was creating a system for engaging and disengaging the power transmitted to the back wheel. This wasn’t a problem as long as you were moving, but once you decided to stop, it quickly became important.

Most early motorcycles used a leather belt to transmit power from the engine to the rear wheel. This belt connected directly to the crankshaft. To give the rider some control over the flow of power, a pulley mounted on a lever was used to tighten the belt. This system proved to be marginally effective, even on the underpowered machines of the time, and it soon became clear that a better system was needed. That system was the clutch. The clutch is a series of springloaded plates that, when pressed together, transmit power from the crankshaft to the transmission.



Early clutches were operated by a foot pedal, like on an automobile, with levers mounted to the gas tank to shift gears in the transmission. This setup proved to be cumbersome and awkward. When the British began exporting motorcycles to the United States with handoperated clutches and foot-operated shifters, U.S. riders soon realized the benefits of such a system, forcing Harley-Davidson to adopt hand clutches and foot shifts for its motorcycles.

Nearly every full-sized motorcycle built since World War I uses a clutch, with a couple of notable exceptions. Honda experimented with a clutchless, or automatic, transmission on its CB 750 in the mid-1970s, then repeated with their Dual-Clutch Transmission (DCT) on VFR1200F, and Moto Guzzi marketed an automatic bike at about the same time. Neither was a sales success. Unless you run across an example of one of these rare bikes, you should probably resign yourself to learning to use a clutch.

Since Gottlieb Daimler constructed the first gasoline-powered motorcycle back in 1885, motorcycles have had carburetors - complex devices that mix gasoline and air into the fuel charge squirted into the combustion chamber. Carburetors, or carbs, as they are usually called, rely on their shape to create the vacuum pressure that provides the energy for this squirt. Although modern carbs are remarkably efficient devices, they share many similarities with the crude device old Gottlieb bolted onto his half-horsepower engine way back when.

Today, most motorcycles have one carburetor for each cylinder, with a few exceptions. The carburetor’s century-long supremacy as the ultimate form of motorcycle induction system has been challenged in the last decade by fuel injection. Fuel injection refers to a system that forces the fuel charge into the combustion chamber with an electronic or mechanical pump of some sort.


The first reliable motorcycle fuel-injection system appeared on BMW’s first four-cylinder motorcycle, the K100 of 1984. Now every engine BMW builds sports fuel injection.

Other makers are jumping on the fuel-injection bandwagon, too. Ducati introduced its first production fuel-injected bike in 1988, the 851 Superbike. Suzuki now offers a large numbers of models with fuel injection. Honda recently introduced its new, Fuel-injected CBR650F, and even Harley-Davidson offers fuel injection on some models.

With the universal acceptance of fuel injection in the automotive world, it might seem odd that motorcycles have been slower to adopt the technology. Fuel injection offers certain benefits, such as greater control over the ratio of the fuel charge and less dependence on atmospheric conditions, but for some reason, motorcycle fuel-injection systems have so far provided less than satisfactory results. The biggest problem seems to be a surging in the engine, which makes it difficult to maintain a steady RPM level.

Such jerky power delivery on a sportbike can be dangerous, since these bikes are often ridden close to their handling limits. When you’re riding right on the edge, an unexpected surge in power while heeled over in a hard corner can lead to a trip to the emergency room.

The problems with fuel-injection systems on motorcycles seem to involve cost and size. Automotive systems incorporate many computerized controls not found on systems used on motorcycles. However, automotive systems tend to be too large to work in the compact space available on a motorcycle, and they are also quite expensive. Although some bikes still suffer driveability problems with fuel injection systems, more and more bikes are using such systems, most with no ill effects at all. Modern technology has finally made fuel injection a viable option on motorcycles.

The top end of a motorcycle is where the internal-combustion process takes place. The top end consists of the pistons, the cylinder block, and the head, which contains the valve train. As mentioned earlier, pistons are metal slugs that move up and down in the cylinders. The energy created by burning the fuel charge (a mixture of gasoline and air) acts on the tops of the pistons (known as the crowns) to make your bike move. Pistons are both simple and complex devices, but for the sake of this discussion, I’ll stick with this simple definition.

The cylinder block is a rather simple device, too—a hunk of aluminum with holes bored through it, inside which the pistons move up and down. This hunk serves two purposes :

1. It channels the pistons’ energy and forces them to move up and down (rather than flying all over the place, which would not help make your motorcycle move).
2. It dissipates the intense heat created by the burning fuel charge and the friction caused by the motion of the pistons. This is done by some sort of coolant circulating throughout the block, by cooling oil being sprayed on the hot spots on the piston, or by air flowing over the outside of the block. Usually, some combination of the three methods effectively cools the engine.

The valve train is the most convoluted and confusing system in the top end. It consists of a cam, which is a rod with lobes on it that opens the valves. Valves are devices consisting of metal stems with flat disks on one end. They ride in metal tubes, called valve guides, and open and close at precise moments to let unburned fuel charges into the combustion chambers and to let the waste gases created during the combustion process exit the combustion chambers. There are two basic types of valve trains: overhead cam systems and pushrod systems. There are several varieties of each system, but they all share some common traits.

Most modern bikes use overhead cams. In this type of valve train, the cams are located above the valves and act on them through a system of rocker arms, or the cam lobe acts directly on the valve. Rocker arms are metal levers that rotate on a small shaft like an upside-down teeter-totter; the cam lobes push one side of the rocker up, causing the other side of the rocker to push the valves down, opening them up.

The pushrod system has cams located below the combustion chambers, usually in the engine cases, that act on pushrods, long, metal rods connected to the rocker arms located above the valves. Harley-Davidson and Moto Guzzi are the only two major manufacturers still using this method of valve actuation in its traditional form. BMW uses a hybrid camin- head system, which locates the cam in the cylinder head but below the valves. This system uses short pushrods to open the valves.

Overhead cams have a more positive action (less slop in the system) and allow the engine to operate at a higher rate of revolutions per minute (RPM) than can pushrod engines. The term RPM refers to the number of times a crankshaft spins around each minute. Being able to run at higher RPMs means an engine will put out more overall power—the faster your crankshaft can spin, the faster your rear wheel will turn, and the faster you will be able to go.

One advantage of Harley’s pushrod system is easy maintenance. Harleys use hydraulically adjusted tappets (small metal slugs between the cams and the pushrods) that eliminate the need for periodic valve adjustments. Some overhead-cam designs also use hydraulic-valve adjustments, but most require periodic manual adjustments.

I like to compare motorcycle components to the human body to make it easier to envision. The bottom end is the entrails of a bike. This is where all the commotion in the engine is converted into forward motion. The two clam-shell-like metal halves that surround the bottom end are called cases. All motorcycle engine bottom ends contain at least one crankshaft (on certain designs, two crankshafts occupy the space within the engine cases, but these are rare, especially in the United States).

" The bottom end of a bike refers to the bottom part of the engine, where the crankshaft and (usually) the transmission reside. The top end refers to the upper part of the engine, which contains the pistons, cylinders, and valve gear. "

The crankshaft is connected via connecting rods to the pistons, which are the slugs moving up and down within the cylinders (the hollow shafts in the top end inside which internal combustion occurs). The connecting rods attach to the crankshaft on eccentric journals, or metal shafts, and their up-and-down movement is converted into a circular motion through the design of these journals.

As you’ll see in the next chapter, the design of the crankshaft does much to give the engine its character; for example, it’s the design of the crankshaft that gives Harley- Davidsons their characteristic rumbling sound (it’s what also makes Harley engines vibrate like washing machines with unbalanced loads).

The Transmission

On most modern motorcycles, the circular motion created by the crankshaft setup is transmitted to the transmission through a series of gears or by a chain. For all practical purposes, you can think of the transmission of a modern motorcycle as part of the bottom end. The crankshaft and the gearset usually reside inside the same cavity within the cases. This is called a unitized transmission, and since the 1950s and 1960s, it has been a part of just about every motorcycle engine designed.

" A unitized transmission (often referred to as a “unit transmission”) is a transmission that is an integral part. "

One notable exception is Harley-Davidson, the only company still manufacturing motorcycles that use separate engines and transmissions, connected by a primary drive. The primary, as it is called, consists of a sprocket attached to the crankshaft that rides outside the engine cases, in a case of its own (called the primary case). This case is connected to the transmission, which is located behind the engine, via a primary chain.

Harley’s primary drive system presents added maintenance chores: The primary chain must be periodically adjusted, a rather difficult process that creates more opportunities for things to go wrong. The exposed components are also more vulnerable to damage than components protected within the cases. No one knows for certain why Harley continues to use this archaic setup, but if I had to guess, I’d say it’s purely for looks.

" A primary drive is a drive chain connecting the engine’s crankshaft to its transmission. "

The transmission is an integral part of the bottom end on most motorcycles, but it is really a separate system. Transmission design varies from bike to bike, but most share some basic characteristics. Each transmission contains a gearset, which, as you might have guessed from the name, is a set of gears. Designers use complex mathematical equations between the diameter of these gears and a variety of other parts on the motorcycle to give a bike certain characteristics.

These gears are engaged by shifting a lever with your left foot, which moves forks inside the transmission, which in turn move the gears within. If you have any trouble with the transmission, the odds are it will involve those forks.

Motorcycles are mechanical devices. Bikes that have tried to hide their mechanical nature have usually failed to win over the motorcycling public. Philip Vincent, founder of the Vincent-HRD motorcycle company, discovered this in 1954 when he tried to sell versions of his magnificent Vincent motorcycles cloaked in fiberglass bodywork. The failure of the Black Prince and Black Knight helped seal Vincent’s fate, and the last Vincent motorcycle was constructed at Vincent’s Stevenage factory in 1955.


Subsequent fully enclosed motorcycles have fared little better than the Vincent. Ducati marketed a fully enclosed series of bikes, the Pasos and 907 I.E., in the late 1980s and early 1990s, but these never set motorcycle buyers on fire. As a result, Ducati now offers several models with small half fairings (the devices mounted at the front of a motorcycle to protect the rider from the elements) or no fairings at all to better showcase its engines. Honda tested the market for shrink-wrapped bikes when it introduced the Pacific Coast in 1989. This model did so poorly that it was withdrawn from the market; it was such a competent all-around motorcycle, though, that it rose from the dead and is now back in production.

Other designers learned from the lack of success of these bikes, and newer designs, like the recent wave of sporting twins from Japan, highlight rather than hide their engines. Motorcyclists appreciate a bike’s mechanical nature, and any biker worth his or her leather jacket is well-versed in the anatomy of a motorcycle.

Meeting the Motor

The motor seems a logical place to start when dissecting a bike. Motorcycles are, after all, named for their engines. The engine, more than anything else, gives a motorcycle its character and personality. Looks may stir you to buy a bike, but it is the characteristics of the engine that keep you riding it year after year. As Philip Vincent said, “Motorcycles are supposed to be ridden, and one cannot see the model when one is riding it” (Vincent, An Autobiography, 1976).

The engine proper is usually divided into two parts - the lower portion, called the bottom end, which includes the parts that transmit power to the rear wheel, and the upper portion, called the top end, which is where the internal-combustion process takes place. The engine also includes a system to introduce a fuel charge into the chambers where combustion takes place. This is called the induction system, and consists of either a carburetor (or more likely carburetors), or else fuel injectors, and it works in conjunction with a series of valves that are part of the engine’s top end.