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Unread 07-20-2006, 06:08 PM   #1
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Default The Four Stroke Cycle Explained

This is meant to explain the basics of how a four stroke engine operates.


The four stroke cycle, also known as the Otto Cycle, is known by its four strokes used for the movement of a piston inside a cylinder.

The four strokes are the following (in order):

1. Intake Stroke
2. Compression Stroke
3. Power Stroke
4. Exhaust Stroke

The cycle must begin at the very top of the cylinder known as "Top Dead Center". First the piston goes to the bottom of the cylinder (Intake). The fuel/air mixture is then sucked into the cylinder through the inlet port. The valves then close and the cylinder goes back to the top of the cylinder where it is compressed dramatically (compression). Usually the fuel/air mixture is then ignited by a spark plug. But in diesel engines the mixture ignites out of pure heat and compression. This causes the piston to go back down to the bottom of the cylinder (power). Then the final stroke is the upward movement of the piston where the exhaust valve is opened thus releasing all the remaining gases out (exhaust).

The valves are operated by a camshaft, which is a rod with a series of projecting cams, each with a calculated profile designed to push the valve open by the required degree at the right moment and to hold it open as required as the camshaft rotates. Between the valve stem and the cam is a cam follower, which accommodates variations in the line of contact of the cam. The location of the camshaft varies, as does the quantities. Some engines have overhead cams, or even dual overhead cams, in which the camshaft(s) directly actuate(s) the valves through a cam follower. This design is typically capable of higher engine speeds due to fewer moving parts in the valve train. This configuration is becoming increasingly popular and common. In other engine designs, the cam shaft is placed in the crankcase and its motion transmitted by a push rod, rocker arms, and valve stems.

More to be added later...

Last edited by Apollouser; 07-20-2006 at 06:11 PM.

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Unread 07-31-2008, 08:56 PM   #2
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Nice post but i still think two stroke engines make more power because there is combustion on EACH revolution of the crankshaft.

But the bottom line is that we are still burning fuels, but at a much less amount. So lets support alternative engines, such as the air car.

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Unread 08-02-2008, 02:55 PM   #3
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well yes the two stroke gives more power but the fuel consumption on two stroke is just ridiculous thats why youll only see two strokes on weed trimmers and what not.

Nice post by the way nothing like some info never hurts


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