Bike Basics

What will we see today?

• A typical spec sheet• Engine – What is it?• Types of Engines– Two Stroke– Four Stroke– Wankel/Rotary

• Displacement Calculation• What is Power

Spec Sheet

• Engine Components – Typical Four Stroke Motor– Head• Cams• Camshaft• Valves• Buckets

– Block• Piston• Piston Rings• Con Rod

– Crankcase• Crankshaft• Bearings

• Typical working of an engine– Intake– Air Fuel Compression charge– Ignition– Expansion due to ignition– Reciprocating to Rotary Motion

Typical Two Stroke Motor

This system manages to pack one power stroke into every two strokes of the piston (up-down). This is achieved by exhausting and re-charging the cylinder simultaneously.

• The steps involved here are:– Intake and exhaust occur at bottom dead center. Some form of pressure is

needed, either crankcase compression or super-charging.– Compression stroke: Fuel-air mix compressed and ignited. – Power stroke: piston is pushed downwards by the hot exhaust gases.

Typical Two Stroke Motor

Typical Four Stroke Motor

Engines based on the four-stroke ("Otto cycle") have one power stroke for every four strokes (up-down-up-down) and employ spark plug ignition. Combustion occurs rapidly, and during combustion the volume varies little ("constant volumeThe steps involved here are:• Intake stroke: Air and vaporized fuel are drawn in.• Compression stroke: Fuel vapor and air are compressed and ignited.• Combustion stroke: Fuel combusts and piston is pushed downwards.• Exhaust stroke: Exhaust is driven out.

Typical Four Stroke Motor

Here,

Bore is the diameter measurement of the cylinders in a piston engineStroke refers to the distance the piston travels between BDC and TDC

What is Displacement. How to calculate the CC of an engine

Let’s calculate the CC ourselves

Pulsar 220 DTS-I• Bore: 67 mm• Stroke: 62.4 mm

Displacement = (3.1415/4) * (6.7 *6.7) * (6.24) NOTE: 67 mm has been converted to cm by dividing it by 10. Same for

StrokeDisplacement = 219.99421 ~ 220 CC (cubic centimeters)

Types of engines• Perfectly Square - equal bore and stroke dimensions, giving a bore/stroke

value of exactly 1. – Example – Bugatti Veyron

• Oversquare or Short Stroke - bore is larger than stroke, giving a bore/stroke value of greater than 1. – Allows for larger/more valves.– Lower Friction Losses (less piston travel)– High engine speeds.– Example – Formula 1 and MotoGP engines.

• Undersquare or Long Stroke – bore is smaller than stroke, resulting in bore/stroke value of less than 1. – More compact– Higher Friction Losses– Typically tuned to make torque at lower engine speeds– Example – Enfield Bullet

• What is Compression Ratio

The compression ratio of an internal-combustion engine is a value that represents the ratio of the volume of its combustion chamber; from its largest capacity to its smallest capacity. For example, the compression ratio of a Bajaj Pulsar 220 DTS-I is 12.8:1

The ratio is calculated by the following formula:

where b = cylinder bore (diameter) s = piston stroke length Vc = clearance volume. It is the volume of the combustion chamber (including head

gasket). This is the minimum volume of the space at the end of the compression stroke, i.e. when the piston reaches top dead center (TDC). Because of the complex shape of this space, it is usually measured directly rather than calculated.

What is Power?• James Watt pioneered engine power measurement• Watt determined that a horse could turn a mill wheel 144 times in an hour (or

2.4 times a minute)• The wheel was 12 feet in radius, therefore the horse travelled 2.4 × 2π × 12 feet

in one minute• Watt judged that the horse could pull with a force of 180 pounds

• This was rounded off to 33,000• Brake horsepower (bhp) is the measure of an engine's horsepower without the

loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc

Power and Torque explained

• Torque: A simplified way of looking at torque is to say it is the amount of force from the engine that turns the rear wheel in a turning motion.

• Power: Is the rate of doing work. Normally can be calculated from the torque and RPM.

Typical 150cc Indian Bikes

Bike R15 Pulsar 150 FZ – 16 Discover 150

RTR 160 Unicorn Average

Displacement 149.8 149.01 153 144.8 159.7 149.1 150.9

Peak Power 17 15.04 14 12.8 15.2 13.3 14.55

Peak Power RPM

8500 8500 7500 7500 8500 8000 8083

Peak Torque 15 12.7 13.6 12.7 13.1 13 13.35

Peak Torque RPM

7500 6500 6000 5500 6000 5500 6166

Weight 131 143 126 121 136 146 133

Power:Weight Ratio

129 105 111 105 111 91 108

What Next?

• Cooling Systems• Clutches• Gearboxes