Four-Stroke Engine Basics

• Cars• Trucks• Semis• Tractors• Airplanes • Motorcycles • Lawnmowers

The Basics

• A four-stroke engine:– Is an internal combustion engine– Converts gasoline into motion– Is the most common car engine type– Is relatively efficient 20% – 4 piston strokes per cycle– 2 crankshaft revolutions per cycle

Basic ComponentsIntake Valve

Valve Cover

Intake Port

Head

Coolant

Engine Block

Oil PanOil Sump

Crankshaft

Camshaft

Exhaust Valve

Spark Plug

Exhaust Port

Piston

Connecting Rod

Rod Bearings

The 4-Stroke Cycle

• 1. • 2. • 3. • 4.

Intake

Compression

Combustion

Exhaust

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Intakeprocess of filling the cylinder with the proper air-fuel mixture through the intake valve.

Back

Compression the process of compressing the air-fuel mixture in the cylinder to make it more combustible

Back

Combustionthe process of igniting the compressed air-fuel mixture to create motion and the over all power of the engine.

Back

Exhaustthe process of releasing the exhaust out of the cylinder through the exhaust valve.

How Stuff Works Animation

• http://auto.howstuffworks.com/engine1.htm

• Engine Block- cast in one piece. The basis for most of the parts of the engine.

Back

• Valve Cover- Protects the valves and the valve springs. Keeps dirt out and lubricating oil in.

• Head- a platform containing most of the parts of the combustion chamber.

• Intake Valve- opens at the proper time to let in air and fuel.

• Intake Port- the passageway in a cylinder head for the fuel and air to pass through.

Exhaust Valve- open at the proper time to release the exhaust

Exhaust Port- the passageway in a cylinder head, for the exhaust to pass through

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Valve Guide• Controls the position of the valves

Lubrication

• Oil Pan where the oil is collected and recirculated primarily for lubricating the crankshaft and rod bearing

• Oil Sump where the oil is stored for lubrication

Camshaft- a round shaft with lobes, that rotates to open and close the fuel and exhaust valves.

Aligned with crankshaft gear for proper timing

Spark Pluga device, inserted into the combustion chamber for firing an electrical spark to ignite air-fuel mixture

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Cylinder

• Three types– Cast aluminum– Cast aluminum with cast

iron sleeve– Cast iron

• Usually use a cross-hatch finish to improves ring lubrication

Pistonthe part of the engine that moves up and down in the cylinder converting the gasoline into motion

• Piston Rings-Keep tight seal against cylinder wall

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Ring Grooves• Ring grooves are machined

grooves in the piston designed to hold the rings.

• Ring lands are the areas of the piston between the ring grooves.

• The clearance between the rings and the ring lands is critical.

Connecting Rod- links the piston to the crankshaft.Rod Bearing- used to reduce friction to the rod and crankshaft

Crankshaft- converts the up and down (linear) motion of the piston into a turning, or rotating motion

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Crankcase Breather• Maintains pressure in the

crankcase at less than ambient pressure to assist in the control of oil consumption.

• Excessive blow by renders the breather useless.

• Old engines vent to the atmosphere.

• New engines vent to the carburetor.

Application

• Now that you understand the basics of four-stroke engines, how can you use this information in the real world?

Back Quiz

• Lets take a quiz to see what you have learned!

Back Quiz

1. The ____ controls the amount of intake and the release of exhaust.

a. headb. valvesc. coolantd. connecting rod

2. The _____ Cycle is the ignition of the compressed fuel-air mixture.

a. Exhaustb. Combustionc. Compressiond. Intake

3. The most common type of engine?a. diesel enginesb. 2-stroke enginesc. rotary enginesd. 4-stroke engines

4. What part of the engine converts up and down motion into a rotation motion?

a. crankshaftb. pistonc. valve coverd. camshaft

5. What is the name of the part listed?

a. intake valveb. piston c. oil pand. spark plug

• Congratulations! That is the end of your quiz, and the end of your lesson on four-stroke engines.

Next

Four Stroke Chart Stroke Piston Movement Intake Valve Exhaust Valve

Compare & Contrast 2 & 4 Cycle Engines