Four stroke gas engines
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Four Stroke Gas Engines. The four strokes of a internal combustion engine are:. Intake. Compression. Power. Exhaust. Each stroke = 180 ˚ of crankshaft revolution. Each cycle requires two revolutions of the crankshaft (720˚ rotation), and one revolution of the camshaft to complete

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Four stroke gas engines
Four Stroke Gas Engines

The four strokes of a internal combustion engine are:

  • Intake

  • Compression

  • Power

  • Exhaust

Each stroke = 180˚ of

crankshaft revolution.

Each cycle requires two revolutions

of the crankshaft (720˚ rotation), and

one revolution of the camshaft to complete

(360˚ rotation).

Intake stroke
Intake Stroke

First Stroke

The piston moves down the cylinder

from TDC (Top Dead Center) to BDC

(Bottom Dead Center).

This movement of piston causes low

air pressure in the cylinder (vacuum)

Mixture of Air and Fuel in the ratio

of 14.7 : 1 (air : fuel) is drawn into

the cylinder.

Intake valve stays open and the

Exhaust valve stays closed during

this stroke.

Compression stroke
Compression stroke

Second stroke

The piston moves from BDC to TDC

Intake and exhaust valves stay closed

Air and fuel mixture is compressed

8:1 to 12:1

The pressure in the cylinder is raised

Power stroke
Power stroke

Third stroke

At the end of compression stroke

the sparkplug fires, igniting the air/fuel


Both the valves stay closed in

this stroke.

The expanding gases from the

combustion in the cylinder

(with no escape) push the piston


The piston travels from TDC to BDC.

Exhaust stroke
Exhaust stroke

Fourth and last stroke

The momentum created by the

Counter-weights on the crankshaft,

move the piston from BDC to TDC.

The exhaust valve opens and

the burned gases escape into the

exhaust system.

Intake valve remains closed.

Four strokes
Four strokes

All four strokes

Valve timing
Valve Timing

The ratio of cam to crank sprocket is 2:1

For every two revolutions of

Crankshaft, the Camshaft turns once.

Chain driven

Belt driven

Gear driven


The job of the carburetor is to

accurately meter extremely tiny

quantities of fuel and mix it with

the air entering the engine, so that

the engine runs properly.

It works on the principle of

High and low pressure

High and low pressure is created

with the help of Venture

Ignition system
Ignition system

Provides high voltage surges – as high as 47,000 volts to the spark plug

  • Parts

  • permanent magnet.

  • armature assembly.

  • breaker points.

  • condenser.

  • spark plug.


In the engine, dippers on the connecting-rod bearing caps enter

the oil pan with each crankshaft revolution to produce the oil splash.

A passage is drilled in each connecting rod from the dipper to the

bearing to ensure lubrication.(used only on 4-stroke small engines)


Air cooled

Fins are used to dissipate heat

Liquid cooled

Coolant is used to dissipate heat.