Motorcycles 101 – Anatomy, Engine-Types, and Drive

Motorcycle Basics
This post may contain links to affiliates of MyLifeExplored. These links help support the maintenance costs of MyLifeExplored and cost you absolutely nothing. A list of my current affiliates may be found here.

If you’ve read “Why I Started Ride Motorcycles” then you may assume that motorcycles are fairly simple machines, and you’re not wrong in making that assumption. Maybe the simplicity purported in this assumption has made you want to buy a motorcycle; maybe you’ve been riding for years and want to understand the machine between your legs; or, maybe you simply enjoy learning about various topics. Well, the purpose of this post and series is to appeal to all of these reasons and open up the world of motorcycles and the engineering feats propelling the industry to all who are interested. We begin with an introduction to motorcycles where I hope to get down to the basics and answer questions from “what exactly is a cylinder”to “what does it mean when a motorcycle has a 1,100 cc V-Twin engine”. The Motorcycle 101 series will later include information for first-time buyers and engineer-minded individuals alike. We’ll see posts such as “Motorcycle Gear 101,” “Traction Control 101,” and “Horsepower vs Torque.” Make sure to subscribe to receive email notifications and updates for this series.

Bikes are simple – two wheels, a power source, and a place for the operator; but, it also represents mankind’s ingenuity.

MyLifeExplored

Motorcycle Anatomy


http://www.calsci.com/motorcycleinfo/Intro/controls.gif

Motorcycle Types


 Body PositionFoot PositionSeat HeightRiding Purpose
StandardUpright, semi-forwardUnderneathLowGeneral
SportForward leaningBehindHighTrack days, general, highway
Sport TouringForward leaningBehindHighTouring, highway
TouringUprightUnderneath, runner board forwardMediumTouring
CruiserRelaxed, backward leaningForwardLowGeneral, highway, touring
ADV/Dual SportUprightUnderneathMedium/HighOff road, general, highway, touring

This is not under any circumstances intended to be a comprehensive list. Instead, it’s a general table for broad characteristics and body types that many other styles of motorcycles derive from. For example, choppers and bobbers derive from the relaxed, low saddle position of cruisers whereas cafe racers reflect the frame of standard motorcycles but undergo aftermarket modifications to alter the seat position from upright to forward-leaning.

* Rideapart.com receives all credit for all images used here.

Engines


Victoria has a 919cc, in-line four, four-stroke engine.
MyLifeExplored

This lingo can seem confusing and like a foreign language; but, it’s actually quite simple. In order, these terms simply refer to the combined surface area of each cylinder (919 cubic centimeters, or cc), the placement or arrangement of the cylinders (in-line), the amount of cylinders (four), and the required amount of directional changes for a complete power cycle (four-stroke). Understanding the anatomy of an engine and the general mechanics that make your bike go forward will hopefully resolve your apprehension and clear up any confusion.

Engine Anatomy

Motorcycle Engine/Cylinder Anatomy
Cylinder Diagram. Source: http://www.animatedengines.com/otto.html

cylinder is a space where internal combustion of modern engines occurs; so, if a motorcycle has four cylinders, there are four spaces where the combustion process occurs. Surface area is one of the most important factors that determine the number of cylinders used for motorcycle engines. The more cylinders used means a higher amount of surface area for pressure to build during the ignition stroke. As the number of cylinders increases, so does the weight; the weight of the engine begins to surpass the power generated by additional cylinders, though. This is why most motorcycle engines have two to four cylinders.

piston is housed in each cylinder and is moved up and down by the connecting rod.

The connecting rod (con-rod) is attached to the piston and crank shaft. As the crank shaft rotates, the piston is either pushed toward or away from the spark plug.

The inlet valve opens for fuel vapor to enter the cylinder from the carburator (not pictured, but carburators regulate the fuel-to-air ratio for fuel vapor).

The exhaust valve opens after internal combustion has occurred in order to expel the resulting waste.

2 vs 4 Stroke

As an introduction, we are only concerned with four-stroke engines because two-stroke bikes are essentially obsolete due to emission standards. Modern bikes use the four strokes to complete a “power cycle.” Each time a piston changes direction is considered a “stroke” and each stroke has a different purpose: induction – compression – ignition – exhaust; or, suck – squeeze – bang – blow.

Motorcycle Engine Basics
4-Stroke Animation
  1. Induction/Suck: A mixture of fuel and air – fuel vapor – is sucked into the cylinder from the carburetor via the inlet valve as the Con-Rod pulls the piston downward, away from the spark plug
  2. Compression/Squeeze: The piston is shoved upward, toward the spark plug and the fuel vapor is compressed and the cylinder becomes pressurized.
  3. Ignition/Bang: The spark plug ignites as the piston is pulled back toward the crank, causing an explosion in the cylinder. This is also known as the “power stroke” as it is where the energy/power is produced.
  4. Exhaust/Blow: The piston moves upward and shoves the burnt gases – fumes/exhaust – out of the cylinder.

Displacement and Engine Size – CCs

Victoria’s model – 919 – signifies the volume of her cylinders measured in cubic centimeters. A larger cylinder typically denotes a more powerful bike. I say typically because factors such as gear ratios, powerbands, and torque also affect a bike’s power.

Cylinder Arrangement – Inline, V, and Boxer Engines

  • An inline engine has all of its cylinders in the same plane – or, simply put, the cylinders are placed in a straight line which, in most cases, span the width of the motorcycle. Inline engines are most commonly two cylinder (aka parallel twin), three cylinder (aka triple), or four cylinder (inline-4) engines.
  • V engines bank their cylinders opposite each other with the crankshaft at the bottom and between the cylinder banks, forming a “V” shape. Vs and boxers are commonly two, four, or six cylinder engines as they require an even number of cylinders for proper weight distribution.
  • Boxers are an exaggerated form of V engines. Boxers follow the same principle – crankshaft between the cylinder banks – but flatten the “V” shape out to have an engine parallel with the ground.
 StrengthsWeaknessesCommonly found on
InlineMechanical simplicity
high horsepower
Lacks torque
Width
Japanese sport bikes
VTorque
Wide powerband
Low center of gravity
Less power per cylinder
Cooling
Vibration
Heavier than Inline engines
V-Twin: American cruisers, Ducati, and Moto Guzzi

V-4: High-end sport/sport-touring bikes
BoxerLots of torque
Well-balanced
Smooth power delivery
Wide - very, very, wide.BMW

Carburetors vs Fuel Injection

Carburetors are the original mechanism used to mix fuel and air to the proper proportion. Carbs use air flow and pressure to create this mixture and are essentially obsolete due to the creation of electronic fuel injection (EFI). Motorcycles with EFI use a computer instead of air flow and pressure to create the proper fuel/air mixture. Both carbs and EFI systems inject fuel into a motorcycle’s cylinders during the first stroke.

Air vs. Liquid Cooled Motorcycles

  • Air cooled engines have no radiators, fans, coolant, etc. Instead, the engine is cooled by air flowing around the engine and into the header’s fins. Because there is no actual cooling system in place, no maintenance is required. This is simplicity at its best. There are, however, major drawbacks that come with this simplicity. Low speed riding conditions, such as city commuting and stop-and-go traffic, can cause the engine to regularly overheat because of the lack of air flowing around the engine. Also, the power generated by an air-cooled engine is limited by the ability for the air to cool the engine down. As power increases, so does the engine’s temperature. Air becomes less effective as this happens and the bike’s power suffers.
  • Liquid cooled engines circulates coolant/water around the engine. The liquid absorbs the heat generated by the engine and carries it to the radiator where it is then dispersed into the air. While liquid cooled bikes require a radiator, pumps, hoses, etc., there are major advantages to liquid cooling. Primarily, there is less risk for the bike to overheat in stand-still situations. When stationary, heat is stored in the radiator and cannot be expelled into the air, similar to air-cooled engines; but, liquid cooled bikes have an automatic fan that engages and cools the radiator when the bike reaches a certain temperature.

Chain vs. Belt vs. Shaft Drive


Chains, belts, and shafts connect the bike’s transmission to the rear wheel and are the final link in the procession of power generated by the 4-stroke process.

Chains are the cheapest and most common form of final drive. The relative cost and ability to customize sprocket sizes, teeth, etc. in order to generate more power have helped propel the chain and sprocket to the most common form of drive for motorcycles. They do, however, require the most care and maintenance. The teeth of a bike’s sprockets becomes worn and filed by the chain resulting in the necessity to completely replace the sprockets when a chain fails or needs to be replaced.

Belt-driven motorcycles prescribe to the same mechanical concepts as chain-driven bikes, but use a belt instead of chain and sprockets. This system resembles timing-belt systems found in cars and requires less maintenance than chain motorcycles as belts to stretch over time.

Shaft-driven motorcycles are connect the transmission to the rear wheel with an enclosed shaft. Shaft-driven motorcycles are typically more expensive, but maintenance on the final drive (shaft) is virtually non-existent as shafts usually last for the entire life of the motorcycle.

Valuable Resources


These are some of the sources that I used while writing this, ones that I intend to use for future “Motorcycle 101” posts, and ones that I use daily.

The Essential Guide to Motorcycle Maintenance

Race Tech’s Motorcycle Suspension Bible

Motorcycles: Fundamentals, Service, and Repair

http://www.Rideapart.com

http://BikeBandit.com

Liked this post? Didn't like it? Let me know below!