How a four stroke engine works
I've notice a few new and young riders from time to time struggle with understanding the science of how their four stroke engine works. The reason it's called a four stroke is as follows:
1-Intake stroke 2-Compression stroke 3-Combustion/power stroke 4-Exhaust stroke
Hence the term "four stroke" The following diagram shows this sequence:
This is a synopsis of these functions:
GENERAL OPERATION:
Intake stroke (image 1)
As The piston is pulled down during The intake stroke, The camshaft opens The intake valve and a fresh charge of fuel/air mix is drawn into The cylinder. The intake valve closes when The piston reaches The bottom of its downward stroke.
Compression stroke (image 2)
The piston now begins to move upward and starts to compress The air/fuel mixture in The cylinder. Both valves are closed. This continuing upward motion compresses The mixture to a certain PSI, and certain atmospheric pressure (The compression "ratio"). As The piston reaches The top of The cylinder The spark plug fires and ignites The compressed mixture.
Power stroke (image 3)
The fuel air mixture now BURNS very rapidly, increases in pressure generated by combustion and forces the piston downward in The cylinder. Both valves are still closed.
Exhaust stroke (image 4)
Upon completion of The power stroke The piston starts to move upward again and now The exhaust valve starts to open. The continuing upward movement forces The hot burned gases out past The exhaust valve. When The piston reaches The top of The cylinder The exhaust valve closes. The piston starts to go back down and The cycle repeats itself.
It's important to understand when combustion must take place in order to not only improve your machines performance but also to keep from damaging your engine. Once you get your head around this, then the reasons for proper timing of your ignition system become quite clear.
First off you don't want the fuel/air mixture to ignite wile your piston is on it's upstroke during the compression stroke. This has a tell tail sound you may have heard as "pinging" and also a loss of power. What's happening is your piston is fighting a downward pressure wile it's trying to move upwards. This can lead to overheating which can damage your piston and possibly cause the dreaded "Holed piston". Your piston can get so hot it starts to melt and the pressure blows a hole in it! Ouch!!!
Second you don't want the air/fuel mixture to ignite to late on it's combustion/power stroke and possibly burn a exhaust valve etc... You can tell this might be happening by loss of power and your engine will sound and act funny,But that's not funny at all! Is it? . Once you get your bike running well, over time you'll start to know how well it's doing by listening and driving it. You'll become one with the Machine!!! BWAAAAAhAhAAA!!!!!
Well that's how your Triumph four stroke 650 works or any other four stroke for that matter. This simple knowledge will help you better understand the following links on timing your engine and other maintenance issues: