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The Heartbeat of Harley


	The Heartbeat of Harley 88-B "Fathead" (88 Cubic Inches ~ Balanced) Suck ... Squeeze ... Bang ... Blow Today, cars, trucks, motorcycles, construction machinery and many others most commonly use a "four-stroke" cycle internal combustion engine (ICE). The four strokes refer to intake, compression, combustion and exhaust strokes that occur during two crankshaft rotations per working cycle of the engine. The four steps in this cycle are often informally referred to as "suck ... squeeze ... bang ... blow." Now, next time you attend a boring cocktail hour, or finger-tapping, eye-brow raising corporate meeting, you can break the ice and impress your friends and associates with your knowledge of the internal combustion engine ... and the creative terminology you've come up with to describe it. So, without further ado, let's take a close look at what is going on inside your vehicle's engine ... (Read Discussion) Jim Baines
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4-Stroke Cycle

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September 06, 2008

- Jim Baines

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( SUCK) INTAKE ~ The intake stroke begins with the piston near the top of its travel. As the piston begins its descent, the exhaust valve closes fully, the intake valve opens and the volume of the combustion chamber begins to increase, creating a vacuum (thus the term SUCK for this cycle). As the piston descends, an air/fuel mixture is drawn from the fuel injectors into the cylinder through the intake manifold. The intake stroke ends with the intake valve closed just after the piston has begun its upstroke.

(SQUEEZE) COMPRESSION ~ As the piston ascends, the air/fuel mixture is forced into the small chamber machined into the cylinder head. This compresses the mixture (SQUEEZE) until it occupies 1/8th to 1/11th of the volume that it did at the time the piston began its ascent. This compression raises the temperature of the mixture and increases its pressure, increasing the force generated during the ignition cycle.

(BANG) IGNITION ~ The air/fuel mixture is ignited (BANG) by the spark plug just before the piston reaches the top of its stroke so that a large portion of the fuel will have burned by the time the piston begins ascending again. The heat produced by combustion increases the pressure in the cylinder, pushing the piston down with great force. This is the cycle that actually creates power in an engine and is also commonly referred to as the POWER stroke..

(BLOW) EXHAUST ~ As the piston approaches the bottom of its stroke, the exhaust valve begins opening and the pressure in the cylinder begins to force the gasses out around the valve. The ascent of the piston then forces nearly all the rest of the unburned gasses from the cylinder (BLOW). The cycle begins again as the exhaust valve closes, the intake valve opens and the piston begins descending and bringing a fresh charge of air and fuel into the combustion chamber.

Remember that this is a basic explanation of how the internal combustion engine works. Variations from this diagram include multiple valve and/or spark plug/fuel injector configurations for increased efficiency and domed pistons for higher compression ratios, to name just a few. But the basic process of SUCK-SQUEEZE-BANG-BLOW is the same for all four-stroke engines.