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How the Engine Works

A basic explanation of the internal parts of an engine, what they do and how they work.

Before we talk about how the engine ignites the air and fuel mixture we have to understand a little more of what goes on inside the engine. We will discuss the basic four-stroke engine in common use in most cars and light trucks on the road today.

Most people refer to their engines as a four-cycle engine. This is not really true. It is a four-stroke, one cycle engine. That is to say that the Intake stroke, Compression stroke, Power stroke and Exhaust stroke are one engine cycle. When the fourth stroke is completed, the cycle begins again.

The main components involved in this part of the engine are the Crankshaft, Camshaft, Pistons and Rings, Connecting rods, Valves, Cylinder Head, and Timing Belt or Timing chain. All of these parts must operate in perfect time or your engine will not operate. If any one of these parts should fail, major engine damage will result.

The Piston rides inside the combustion chamber, around the piston are a series of piston rings that seal the combustion chamber and allow the piston to move up and down. The piston is connected to the crankshaft with a connecting rod. The crankshaft converts the up and down motion of the piston into a circular motion that is ultimately transmitted to the drive wheels.

The crankshaft is connected to the camshaft by a timing belt or timing chain. In some of the older Chevy six cylinder engines they were connected directly by gears, no belt or chain was used. The timing chain keeps the crankshaft and camshaft in time with each other and is a vital link for smooth engine operation. The crankshaft and camshaft gears are sized so that it will turn twice for every one turn of the camshaft. In some engines the camshaft sits in a galley just above the crankshaft and used push rods that went up the inside of the engine to a rocker arm.

The rocker arm then opens the valve sitting in the head. This is known as an OHV or overhead valve arrangement. In an OHC or overhead cam arrangement, the camshaft is in the cylinder head and opens the valves directly. In a DOHC, there is one cam for the Intake valves and one for the Exhaust valves. In a V type engine this means there are four camshafts, two in each cylinder head. The camshaft has a series of lobes that determine when and for how long the valves open. Each valve has it's own lobe. In engines with a mechanical fuel pump there will be an extra lobe to operate the pump.

Okay, now we have an idea of the parts involved, let's take a look at what happens. The first stroke is the Intake stroke. In this stroke, the camshaft opens the intake valve; the crankshaft pulls the piston down creating a vacuum in the combustion chamber and draws in the air/fuel mixture.

On the Compression stroke the intake valve closes and the piston moves up, compressing the air/fuel mixture. The spark plug fires and the air/fuel mixture begins to burn. In the Power stroke the expanding gases from the combustion of the air/fuel mixture pushes the piston down.

Finally we have the Exhaust stroke. The piston again moves up, the camshaft opens the exhaust valve and the burnt fuel is pushed out of the combustion chamber. When the cycle is complete, the intake valve opens and the cycle begins again.

All of this happens extremely fast. At idle, this happens about 700 to 800 times a minute. At about 60 miles per hour, this happens about 2,000 times a minute. Temperatures inside the combustion chamber can reach as high as 3,000 F. So you can get an idea of how important it is to keep everything in the oil and cooling system in good condition.

One engine I won't go into details about, but proved to be a viable alternative to the standard reciprocating engine is what is called the Wankel engine, also known as the rotary engine. This was used with some success in the Mazda RX 7 for a number of years. It was a powerful engine that was extremely smooth operating and relatively fuel-efficient.

There are also 2 cycle engines that operate a little differently. They are not used in a production automotive application but are very common in snowmobiles, chain saws, some motorcycles, and gas powered tool applications. The big advantage being that they can be operated in any position, even upside down.

Intake stroke
Compression stroke
Power stroke
Exhaust stroke

Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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