Four Stroke Gas Engines The four strokes of

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Four Stroke Gas Engines The four strokes of a internal combustion engine are: •

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 First Stroke The piston moves down the cylinder from TDC (Top Dead

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 Second stroke The piston moves from BDC to TDC Intake and exhaust

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

Third stroke Power stroke At the end of compression stroke the sparkplug fires, igniting

Third stroke Power stroke At the end of compression stroke the sparkplug fires, igniting the air/fuel mixture. Both the valves stay closed in this stroke. The expanding gases from the combustion in the cylinder (with no escape) push the piston down. The piston travels from TDC to BDC.

Exhaust stroke Fourth and last stroke The momentum created by the Counter-weights on the

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 All four strokes

Four strokes All four strokes

Four Cylinder Engine

Four Cylinder Engine

Valve Timing The ratio of cam to crank sprocket is 2: 1 For every

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

Carburetor The job of the carburetor is to accurately meter extremely tiny quantities of

Carburetor 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 is created with the help of Venture

Ignition system Provides high voltage surges – as high as 47, 000 volts to

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.

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

Lubrication 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)

Cooling Air cooled Fins are used to dissipate heat Liquid cooled Coolant is used

Cooling Air cooled Fins are used to dissipate heat Liquid cooled Coolant is used to dissipate heat.

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